NuttX Operating System
|
1.0 Introduction |
This manual provides general usage information for the NuttX RTOS from the perspective of the firmware developer.
1.1 Document Overview |
This user's manual is divided into three sections plus a index:
errno Variable
1.2 Intended Audience and Scope |
The intended audience for this document are firmware developers who are implementing applications on NuttX. Specifically, this documented is limited to addressing only NuttX RTOS APIs that are available to the application developer. As such, this document does not focus on any technical details of the organization or implementation of NuttX. Those technical details are provided in the NuttX Porting Guide.
Information about configuring and building NuttX is also needed by the application developer. That information can also be found in the NuttX Porting Guide.
2.0 OS Interfaces |
This section describes each C-callable interface to the NuttX Operating System. The description of each interface is presented in the following format:
Function Prototype: The C prototype of the interface function is provided.
Description: The operation performed by the interface function is discussed.
Input Parameters: All input parameters are listed along with brief descriptions of each input parameter.
Returned Values: All possible values returned by the interface function are listed. Values returned as side-effects (through pointer input parameters or through global variables) will be addressed in the description of the interface function.
Assumptions/Limitations: Any unusual assumptions made by the interface function or any non-obvious limitations to the use of the interface function will be indicated here.
POSIX Compatibility: Any significant differences between the NuttX interface and its corresponding POSIX interface will be noted here.
NOTE: In order to achieve an independent name space for the NuttX interface functions, differences in function names and types are to be expected and will not be identified as differences in these paragraphs.
2.1 Task Control Interfaces |
Tasks. NuttX is a flat address OS. As such it does not support processes in the way that, say, Linux does. NuttX only supports simple threads running within the same address space. However, the programming model makes a distinction between tasks and pthreads:
File Descriptors and Streams. This applies, in particular, in the area of opened file descriptors and streams. When a task is started using the interfaces in this section, it will be created with at most three open files.
If CONFIG_DEV_CONSOLE is defined, the first three file descriptors (corresponding to stdin, stdout, stderr) will be duplicated for the the new task. Since these file descriptors are duplicated, the child task can free close them or manipulate them in any way without effecting the parent task. File-related operations (open, close, etc.) within a task will have no effect on other tasks. Since the three file descriptors are duplicated, it is also possible to perform some level of redirection.pthreads, on the other hand, will always share file descriptors with the parent thread. In this case, file operations will have effect only all pthreads the were started from the same parent thread.
The following task control interfaces are provided by Nuttx:
Function Prototype:
#include <sched.h> int task_create(char *name, int priority, int stack_size, main_t entry, const char *argv[]);
Description: This function creates and activates a new task with a specified priority and returns its system-assigned ID.
The entry address entry is the address of the "main" function of the task. This function will be called once the C environment has been set up. The specified function will be called with four arguments. Should the specified routine return, a call to exit() will automatically be made.
Note that an arbitrary number of arguments may be passed to the
spawned functions. The maximum umber of arguments is an OS
configuration parameter (CONFIG_MAX_TASK_ARGS).
The arguments are copied (via strdup) so that the
life of the passed strings is not dependent on the life of the
caller to task_create().
The newly created task does not inherit scheduler characteristics from the parent task: The new task is started at the default system priority and with the SCHED_FIFO scheduling policy. These characteristcs may be modified after the new task has been started.
The newly created task does inherit the first three file descriptors (corresponding to stdin, stdout, and stderr) and redirection of standard I/O is supported.
Input Parameters:
CONFIG_MAX_TASK_ARG parameters may be provided.
If fewer than CONFIG_MAX_TASK_ARG parameters are
passed, the list should be terminated with a NULL argv[] value.
If no parameters are required, argv may be NULL.
Returned Values:
errno is not set).
Assumptions/Limitations:
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the following similar interface:
int taskSpawn(char *name, int priority, int options, int stackSize, FUNCPTR entryPt,
int arg1, int arg2, int arg3, int arg4, int arg5,
int arg6, int arg7, int arg8, int arg9, int arg10);
The NuttX task_create() differs from VxWorks' taskSpawn() in the following ways:
Function Prototype:
#include <sched.h>
STATUS task_init(_TCB *tcb, char *name, int priority, uint32 *stack, uint32 stack_size,
maint_t entry, const char *argv[]);
Description:
This function initializes a Task Control Block (TCB)
in preparation for starting a new thread. It performs a subset
of the functionality of task_create() (see above).
Unlike task_create(), task_init() does not activate the task. This must be done by calling task_activate().
Input Parameters:
CONFIG_MAX_TASK_ARG parameters may be provided.
If fewer than CONFIG_MAX_TASK_ARG parameters are
passed, the list should be terminated with a NULL argv[] value.
If no parameters are required, argv may be NULL.
Returned Values:
OK, or ERROR if the task cannot be initialized.
This function can only failure is it is unable to assign
a new, unique task ID to the TCB (errno is not set).
Assumptions/Limitations:
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the following similar interface:
STATUS taskInit(WIND_TCB *pTcb, char *name, int priority, int options, uint32 *pStackBase, int stackSize,
FUNCPTR entryPt, int arg1, int arg2, int arg3, int arg4, int arg5,
int arg6, int arg7, int arg8, int arg9, int arg10);
The NuttX task_init() differs from VxWorks' taskInit() in the following ways:
Function Prototype:
#include <sched.h>
STATUS task_activate( _TCB *tcb );
Description: This function activates tasks created by task_init(). Without activation, a task is ineligible for execution by the scheduler.
Input Parameters:
Returned Values:
errno is not set).
Assumptions/Limitations:
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the following similar interface:
STATUS taskActivate( int tid );
The NuttX task_activate() differs from VxWorks' taskActivate() in the following ways:
Function Prototype:
#include <sched.h>
STATUS task_delete( pid_t pid );
Description: This function causes a specified task to cease to exist -- its stack and TCB will be deallocated. This function is the companion to task_create().
Input Parameters:
Returned Values:
errno is not set)
Assumptions/Limitations:
task_delete() must be used with caution: If the task holds resources (for example, allocated memory or semaphores needed by other tasks), then task_delete() can strand those resources.
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the following similar interface:
STATUS taskDelete( int tid );
The NuttX task_delete() differs from VxWorks' taskDelete() in the following ways:
Function Prototype:
#include <sched.h>
void exit( int code );
#include <nuttx/unistd.h>
void _exit( int code );
Description: This function causes the calling task to cease to exist -- its stack and TCB will be deallocated. exit differs from _exit in that it flushs streams, closes file descriptors and will execute any function registered with atexit().
Input Parameters:
Returned Values: None.
Assumptions/Limitations:
POSIX Compatibility: This is equivalent to the ANSI interface:
void exit( int code );
And the unix interface:
void _exit( int code );
The NuttX exit() differs from ANSI exit() in the following ways:
Function Prototype:
#include <sched.h>
STATUS task_restart( pid_t pid );
Description: This function "restarts" a task. The task is first terminated and then reinitialized with same ID, priority, original entry point, stack size, and parameters it had when it was first started.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the following similar interface:
STATUS taskRestart (int tid);
The NuttX task_restart() differs from VxWorks' taskRestart() in the following ways:
Function Prototype:
#include <unistd.h>
pid_t getpid( void );
Description: This function returns the task ID of the calling task. The task ID will be invalid if called at the interrupt level.
Input Parameters: None.
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Compatible with the POSIX interface of the same name.
2.2 Task Scheduling Interfaces |
By default, NuttX performs strict priority scheduling: Tasks of higher priority have exclusive access to the CPU until they become blocked. At that time, the CPU is available to tasks of lower priority. Tasks of equal priority are scheduled FIFO.
Optionally, a Nuttx task or thread can be configured with round-robin
scheduler. This is similar to priority scheduling except that
tasks with equal priority and share CPU time via time-slicing.
The time-slice interval is a constant determined by the configuration
setting CONFIG_RR_INTERVAL.
The OS interfaces described in the following paragraphs provide a POSIX- compliant interface to the NuttX scheduler:
Function Prototype:
#include <sched.h>
int sched_setparam(pid_t pid, const struct sched_param *param);
Description: This function sets the priority of the task specified by pid input parameter.
NOTE: Setting a task's priority to the same value has the similar
effect to sched_yield(): The task will be moved to after all
other tasks with the same priority.
Input Parameters:
pid.
The task ID of the task.
If pid is zero, the priority of the calling task is set.
param.
A structure whose member sched_priority is the integer priority.
The range of valid priority numbers is from SCHED_PRIORITY_MIN through SCHED_PRIORITY_MAX.
Returned Values:
On success, sched_setparam() returns 0 (OK).
On error, -1 (ERROR) is returned, and errno is set appropriately.
EINVAL.
The parameter param is invalid or does not make sense for the current scheduling policy.
EPERM.
The calling task does not have appropriate privileges.
ESRCH.
The task whose ID is pid could not be found.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
Function Prototype:
#include <sched.h>
int sched_getparam (pid_t pid, struct sched_param *param);
Description: This function gets the scheduling priority of the task specified by pid.
Input Parameters:
pid. The task ID of the task.
If pid is zero, the priority of the calling task is returned.
param.
A structure whose member sched_priority is the integer priority.
The task's priority is copied to the sched_priority element of this structure.
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <sched.h>
int sched_setscheduler (pid_t pid, int policy, const struct sched_param *param);
Description: sched_setscheduler() sets both the scheduling policy and the priority for the task identified by pid. If pid equals zero, the scheduler of the calling thread will be set. The parameter 'param' holds the priority of the thread under the new policy.
Input Parameters:
param. A structure whose member sched_priority is the
integer priority. The range of valid priority numbers is from
SCHED_PRIORITY_MIN through SCHED_PRIORITY_MAX.
Returned Values:
On success, sched_setscheduler() returns OK (zero). On
error, ERROR (-1) is returned, and errno is set appropriately:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <sched.h>
int sched_getscheduler (pid_t pid);
Description: sched_getscheduler() returns the scheduling policy currently applied to the task identified by pid. If pid equals zero, the policy of the calling process will be retrieved. * * Inputs: * * Return Value: This function returns the current scheduling policy.
Input Parameters:
Returned Values:
errno is set appropriately:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
errno.
Function Prototype:
#include <sched.h>
int sched_yield( void );
Description: This function forces the calling task to give up the CPU (only to other tasks at the same priority).
Input Parameters: None.
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <sched.h>
int sched_get_priority_max (int policy)
Description: This function returns the value of the highest possible task priority for a specified scheduling policy.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <sched.h>
int sched_get_priority_min (int policy);
Description: This function returns the value of the lowest possible task priority for a specified scheduling policy.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <sched.h>
int sched_get_rr_interval (pid_t pid, struct timespec *interval);
Description: sched_rr_get_interval() writes the timeslice interval for task identified by pid into the timespec structure pointed to by interval. If pid is zero, the timeslice for the calling process is written into 'interval. The identified process should be running under the SCHED_RR scheduling policy.'
Input Parameters:
Returned Values:
On success, sched_rr_get_interval() returns OK (0). On
error, ERROR (-1) is returned, and errno is set to:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
2.3 Task Switching Interfaces |
Function Prototype:
#include <sched.h>
STATUS sched_lock( void );
Description: This function disables context switching by Disabling addition of new tasks to the ready-to-run task list. The task that calls this function will be the only task that is allowed to run until it either calls sched_unlock (the appropriate number of times) or until it blocks itself.
Input Parameters: None.
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the comparable interface:
STATUS taskLock( void );
Function Prototype:
#include <sched.h>
STATUS sched_unlock( void );
Description: This function decrements the preemption lock count. Typically this is paired with sched_lock() and concludes a critical section of code. Preemption will not be unlocked until sched_unlock() has been called as many times as sched_lock(). When the lockCount is decremented to zero, any tasks that were eligible to preempt the current task will execute.
Input Parameters: None.
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the comparable interface:
STATUS taskUnlock( void );
Function Prototype:
#include <sched.h>
sint32 sched_lockcount( void )
Description: This function returns the current value of the lockCount. If zero, preemption is enabled; if non-zero, this value indicates the number of times that sched_lock() has been called on this thread of execution.
Input Parameters: None.
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: None.
2.4 Named Message Queue Interfaces |
NuttX supports POSIX named message queues for intertask communication. Any task may send or receive messages on named message queues. Interrupt handlers may send messages via named message queues.
Function Prototype:
#include <mqueue.h>
mqd_t mq_open( const char *mqName, int oflags, ... );
Description: This function establish a connection between a named message queue and the calling task. After a successful call of mq_open(), the task can reference the message queue using the address returned by the call. The message queue remains usable until it is closed by a successful call to mq_close().
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
Function Prototype:
#include <mqueue.h>
int mq_close( mqd_t mqdes );
Description: This function is used to indicate that the calling task is finished with the specified message queued mqdes. The mq_close() deallocates any system resources allocated by the system for use by this task for its message queue.
If the calling task has attached a notification request to the message queue via this mqdes (see mq_notify()), this attachment will be removed and the message queue is available for another task to attach for notification.
Input Parameters:
Returned Values:
Assumptions/Limitations:
mq_send() or
mq_receive() is undefined when mq_close() is called.
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <mqueue.h>
int mq_unlink( const char *mqName );
Description: This function removes the message queue named by "mqName." If one or more tasks have the message queue open when mq_unlink() is called, removal of the message queue is postponed until all references to the message queue have been closed.
Input Parameters:
Returned Values: None.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <mqueue.h>
int mq_send(mqd_t mqdes, const void *msg, size_t msglen, int prio);
Description:
This function adds the specified message, msg,
to the message queue, mqdes.
The msglen parameter specifies the length of the message in bytes pointed to by msg.
This length must not exceed the maximum message length from the mq_getattr().
If the message queue is not full, mq_send() will place the msg
in the message queue at the position indicated by the prio argument.
Messages with higher priority will be inserted before lower priority messages
The value of prio must not exceed MQ_PRIO_MAX.
If the specified message queue is full and O_NONBLOCK is not
set in the message queue, then mq_send() will block until space
becomes available to the queue the message.
If the message queue is full and NON_BLOCK is set, the message
is not queued and ERROR is returned.
Input Parameters:
mqdes. Message queue descriptor.msg. Message to send.msglen. The length of the message in bytes.prio. The priority of the message.
Returned Values:
On success, mq_send() returns 0 (OK);
on error, -1 (ERROR) is returned, with errno set
to indicate the error:
EAGAIN.
The queue was empty, and the O_NONBLOCK flag was set for the message queue description referred to by mqdes.
EINVAL.
Either msg or mqdes is NULL or the value of prio is invalid.
EPERM.
Message queue opened not opened for writing.
EMSGSIZE.
msglen was greater than the maxmsgsize attribute of the message queue.
EINTR.
The call was interrupted by a signal handler.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
#include <mqueue.h>
int mq_timedsend(mqd_t mqdes, const char *msg, size_t msglen, int prio,
const struct timespec *abstime);
Description:
This function adds the specified message, msg,
to the message queue, mqdes.
The msglen parameter specifies the length of the message in bytes pointed to by msg.
This length must not exceed the maximum message length from the mq_getattr().
If the message queue is not full, mq_timedsend() will place the msg
in the message queue at the position indicated by the prio argument.
Messages with higher priority will be inserted before lower priority messages
The value of prio must not exceed MQ_PRIO_MAX.
If the specified message queue is full and O_NONBLOCK is not
set in the message queue, then mq_send() will block until space
becomes available to the queue the message or until a timeout occurs.
mq_timedsend() behaves just like mq_send(), except
that if the queue is full and the O_NONBLOCK flag is not enabled
for the message queue description, then abstime points to a
structure which specifies a ceiling on the time for which the call will block.
This ceiling is an absolute timeout in seconds and nanoseconds since the
Epoch (midnight on the morning of 1 January 1970).
If the message queue is full, and the timeout has already expired by the time
of the call, mq_timedsend() returns immediately.
Input Parameters:
mqdes. Message queue descriptor.msg. Message to send.msglen. The length of the message in bytes.prio. The priority of the message.
Returned Values:
On success, mq_send() returns 0 (OK);
on error, -1 (ERROR) is returned, with errno set
to indicate the error:
EAGAIN.
The queue was empty, and the O_NONBLOCK flag was set for the message queue description referred to by mqdes.
EINVAL.
Either msg or mqdes is NULL or the value of prio is invalid.
EPERM.
Message queue opened not opened for writing.
EMSGSIZE.
msglen was greater than the maxmsgsize attribute of the message queue.
EINTR.
The call was interrupted by a signal handler.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <mqueue.h>
ssize_t mq_receive(mqd_t mqdes, void *msg, size_t msglen, int *prio);
Description:
This function receives the oldest of the highest priority messages from the message
queue specified by mqdes.
If the size of the buffer in bytes, msgLen, is less than the
mq_msgsize attribute of the message queue, mq_receive() will
return an error.
Otherwise, the selected message is removed from the queue and copied to msg.
If the message queue is empty and O_NONBLOCK was not set, mq_receive()
will block until a message is added to the message queue.
If more than one task is waiting to receive a message, only the task with the highest
priority that has waited the longest will be unblocked.
If the queue is empty and O_NONBLOCK is set, ERROR will be returned.
Input Parameters:
mqdes. Message Queue Descriptor.msg. Buffer to receive the message.msglen. Size of the buffer in bytes.prio. If not NULL, the location to store message priority.
Returned Values:.
One success, the length of the selected message in bytes is returned.
On failure, -1 (ERROR) is returned and the errno is set appropriately:
EAGAIN
The queue was empty and the O_NONBLOCK flag was set for the message queue description referred to by mqdes.
EPERM
Message queue opened not opened for reading.
EMSGSIZE
msglen was less than the maxmsgsize attribute of the message queue.
EINTR
The call was interrupted by a signal handler.
EINVAL
Invalid msg or mqdes
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <mqueue.h>
ssize_t mq_timedreceive(mqd_t mqdes, void *msg, size_t msglen,
int *prio, const struct timespec *abstime);
Description:
This function receives the oldest of the highest priority messages from the message
queue specified by mqdes.
If the size of the buffer in bytes, msgLen, is less than the
mq_msgsize attribute of the message queue, mq_timedreceive() will
return an error.
Otherwise, the selected message is removed from the queue and copied to msg.
If the message queue is empty and O_NONBLOCK was not set, mq_timedreceive()
will block until a message is added to the message queue (or until a timeout occurs).
If more than one task is waiting to receive a message, only the task with the highest
priority that has waited the longest will be unblocked.
mq_timedreceive() behaves just like mq_receive(), except
that if the queue is empty and the O_NONBLOCKabstime points to a structure
which specifies a ceiling on the time for which the call will block.
This ceiling is an absolute timeout in seconds and nanoseconds since the Epoch
(midnight on the morning of 1 January 1970).
If no message is available, and the timeout has already expired by the time of
the call, mq_timedreceive() returns immediately.
Input Parameters:
mqdes. Message Queue Descriptor.msg. Buffer to receive the message.msglen. Size of the buffer in bytes.prio. If not NULL, the location to store message priority.
abstime. The absolute time to wait until a timeout is declared.
Returned Values:.
One success, the length of the selected message in bytes is returned.
On failure, -1 (ERROR) is returned and the errno is set appropriately:
EAGAIN:
The queue was empty and the O_NONBLOCK flag was set for the message queue description referred to by mqdes.
EPERM:
Message queue opened not opened for reading.
EMSGSIZE:
msglen was less than the maxmsgsize attribute of the message queue.
EINTR:
The call was interrupted by a signal handler.
EINVAL:
Invalid msg or mqdes or abstime
ETIMEDOUT:
The call timed out before a message could be transferred.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <mqueue.h>
int mq_notify(mqd_t mqdes, const struct sigevent *notification);
Description: If the "notification" input parameter is not NULL, this function connects the task with the message queue such that the specified signal will be sent to the task whenever the message changes from empty to non-empty. One notification can be attached to a message queue.
If "notification" is NULL, the attached notification is detached (if it was held by the calling task) and the queue is available to attach another notification.
When the notification is sent to the registered task, its registration will be removed. The message queue will then be available for registration.
Input Parameters:
Returned Values: None.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
Function Prototype:
#include <mqueue.h>
int mq_setattr( mqd_t mqdes, const struct mq_attr *mqStat,
struct mq_attr *oldMqStat);
Description: This function sets the attributes associated with the specified message queue "mqdes." Only the "O_NONBLOCK" bit of the "mq_flags" can be changed.
If "oldMqStat" is non-null, mq_setattr() will store the previous message queue attributes at that location (just as would have been returned by mq_getattr()).
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <mqueue.h>
int mq_getattr( mqd_t mqdes, struct mq_attr *mqStat);
Description: This functions gets status information and attributes associated with the specified message queue.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
2.5 Counting Semaphore Interfaces |
Semaphores. Semaphores are the basis for synchronization and mutual exclusion in NuttX. NuttX supports POSIX semaphores.
Semaphores are the preferred mechanism for gaining exclusive access to a resource. sched_lock() and sched_unlock() can also be used for this purpose. However, sched_lock() and sched_unlock() have other undesirable side-affects in the operation of the system: sched_lock() also prevents higher-priority tasks from running that do not depend upon the semaphore-managed resource and, as a result, can adversely affect system response times.
Priority Inversion.
Proper use of semaphores avoids the issues of sched_lock().
However, consider the following example:
At this point, the high-priority Task A cannot execute until Task B (and possibly other medium-priority tasks) completes and until Task C relinquishes the semaphore. In effect, the high-priority task, Task A behaves as though it were lower in priority than the low-priority task, Task C! This phenomenon is called priority inversion.
Some operating systems avoid priority inversion by automatically
increasing the priority of the low-priority Task C (the operable
buzz-word for this behavior is priority inheritance). NuttX
supports this behavior, but only if CONFIG_PRIORITY_INHERITANCE
is defined in your OS configuration file. If CONFIG_PRIORITY_INHERITANCE
is not defined, then it is left to the designer to provide implementations
that will not suffer from priority inversion.
The designer may, as examples:
Priority Inheritance.
As mentioned, NuttX does support priority inheritance provided that
CONFIG_PRIORITY_INHERITANCE is defined in your OS configuration file.
However, the implementation and configuration of the priority inheritance feature
is sufficiently complex that more needs to be said.
How can a feature that can be described by a single, simple sentence require such
a complex implementation:
CONFIG_SEM_PREALLOCHOLDERS.
First of all, in NuttX priority inheritance is implement on POSIX counting
semaphores. The reason for this is that these semaphores are the most
primitive waiting mechanism in NuttX; Most other waiting facilities are
based on semaphores. So if priority inheritance is implemented for POSIX
counting semaphores, then most NuttX waiting mechanisms will have this
capability.
Complexity arises because counting semaphores can have numerous
holders of semaphore counts. Therefore, in order to implement
priority inheritance across all holders, then internal data
structures must be allocated to manage the various holders associated
with a semaphore.
The setting CONFIG_SEM_PREALLOCHOLDERS defines the maximum
number of different threads (minus one per semaphore instance) that can
take counts on a semaphore with priority inheritance support.
This setting defines the size of a single pool of preallocated structures.
It may be set to zero if priority inheritance is disabled OR if you
are only using semaphores as mutexes (only one holder) OR if no more
than two threads participate using a counting semaphore.
The cost associated with setting CONFIG_SEM_PREALLOCHOLDERS
is slightly increased code size and around 6-12 bytes times the value
of CONFIG_SEM_PREALLOCHOLDERS.
CONFIG_SEM_NNESTPRIO:
In addition, there may be multiple threads of various priorities that
need to wait for a count from the semaphore.
These, the lower priority thread holding the semaphore may have to
be boosted numerous time and, to make things more complex, will have
to keep track of all of the boost priorities values in in order to
correctly restore the priorities after a count has been handed out
to the higher priority thread.
The CONFIG_SEM_NNESTPRIO defines the size of an array,
one array per active thread.
This setting is the maximum number of higher priority threads (minus
1) than can be waiting for another thread to release a count on a semaphore.
This value may be set to zero if no more than one thread is expected to
wait for a semaphore.
The cost associated with setting CONFIG_SEM_NNESTPRIO
is slightly increased code size and (CONFIG_SEM_PREALLOCHOLDERS + 1)
times the maximum number of active threads.
sem_destroy()
then. Or what if the thread with the boosted priority reprioritizes itself?
The NuttX implement of priority inheritance attempts to handle all of these
types of corner cases, but it is very likely that some are missed.
The worst case result is that memory could by stranded within the priority
inheritance logic.
POSIX semaphore interfaces:
Function Prototype:
#include <semaphore.h>
int sem_init ( sem_t *sem, int pshared, unsigned int value );
Description: This function initializes the UN-NAMED semaphore sem. Following a successful call to sem_init(), the semaphore may be used in subsequent calls to sem_wait(), sem_post(), and sem_trywait(). The semaphore remains usable until it is destroyed.
Only sem itself may be used for performing synchronization. The result of referring to copies of sem in calls to sem_wait(), sem_trywait(), sem_post(), and sem_destroy(), is not defined.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
Function Prototype:
#include <semaphore.h>
int sem_destroy ( sem_t *sem );
Description: This function is used to destroy the un-named semaphore indicated by sem. Only a semaphore that was created using sem_init() may be destroyed using sem_destroy(). The effect of calling sem_destroy() with a named semaphore is undefined. The effect of subsequent use of the semaphore sem is undefined until sem is re-initialized by another call to sem_init().
The effect of destroying a semaphore upon which other tasks are currently blocked is undefined.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <semaphore.h>
sem_t *sem_open ( const char *name, int oflag, ...);
Description: This function establishes a connection between named semaphores and a task. Following a call to sem_open() with the semaphore name, the task may reference the semaphore associated with name using the address returned by this call. The semaphore may be used in subsequent calls to sem_wait(), sem_trywait(), and sem_post(). The semaphore remains usable until the semaphore is closed by a successful call to sem_close().
If a task makes multiple calls to sem_open() with the same name, then the same semaphore address is returned (provided there have been no calls to sem_unlink()).
Input Parameters:
include/limits.h).
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
Function Prototype:
#include <semaphore.h>
int sem_close ( sem_t *sem );
Description: This function is called to indicate that the calling task is finished with the specified named semaphore, sem. The sem_close() deallocates any system resources allocated by the system for this named semaphore.
If the semaphore has not been removed with a call to sem_unlink(), then sem_close() has no effect on the named semaphore. However, when the named semaphore has been fully unlinked, the semaphore will vanish when the last task closes it.
Care must be taken to avoid risking the deletion of a semaphore that another calling task has already locked.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <semaphore.h>
int sem_unlink ( const char *name );
Description: This function will remove the semaphore named by the input name parameter. If one or more tasks have the semaphore named by name oepn when sem_unlink() is called, destruction of the semaphore will be postponed until all references have been destroyed by calls to sem_close().
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
Function Prototype:
#include <semaphore.h>
int sem_wait ( sem_t *sem );
Description: This function attempts to lock the semaphore referenced by sem. If the semaphore as already locked by another task, the calling task will not return until it either successfully acquires the lock or the call is interrupted by a signal.
Input Parameters:
Returned Values:
If sem_wait returns -1 (ERROR) then the cause of the failure
will be indicated by the thread-specific errno.
The following lists the possible values for errno:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <semaphore.h>
int sem_trywait ( sem_t *sem );
Description: This function locks the specified semaphore only if the semaphore is currently not locked. In any event, the call returns without blocking.
Input Parameters:
Returned Values:
errno.
The following lists the possible values for errno:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <semaphore.h>
int sem_post ( sem_t *sem );
Description: When a task has finished with a semaphore, it will call sem_post(). This function unlocks the semaphore referenced by sem by performing the semaphore unlock operation.
If the semaphore value resulting from this operation is positive, then no tasks were blocked waiting for the semaphore to become unlocked; The semaphore value is simply incremented.
If the value of the semaphore resulting from this operation is zero, then on of the tasks blocked waiting for the semaphore will be allowed to return successfully from its call to sem_wait().
NOTE: sem_post() may be called from an interrupt handler.
Input Parameters:
Returned Values:
Assumptions/Limitations: This function cannot be called from an interrupt handler. It assumes the currently executing task is the one that is performing the unlock.
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <semaphore.h>
int sem_getvalue ( sem_t *sem, int *sval );
Description: This function updates the location referenced by sval argument to have the value of the semaphore referenced by sem without effecting the state of the semaphore. The updated value represents the actual semaphore value that occurred at some unspecified time during the call, but may not reflect the actual value of the semaphore when it is returned to the calling task.
If sem is locked, the value return by sem_getvalue() will either be zero or a negative number whose absolute value represents the number of tasks waiting for the semaphore.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
2.6 Watchdog Timer Interfaces |
NuttX provides a general watchdog timer facility.
This facility allows the NuttX user to specify a watchdog timer function
that will run after a specified delay.
The watchdog timer function will run in the context of the timer interrupt handler.
Because of this, a limited number of NuttX interfaces are available to he watchdog timer function.
However, the watchdog timer function may use mq_send(), sigqueue(),
or kill() to communicate with NuttX tasks.
Function Prototype:
#include <wdog.h>
WDOG_ID wd_create (void);
Description: The wd_create function will create a watchdog by allocating the appropriate resources for the watchdog.
Input Parameters: None.
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the following comparable interface:
WDOG_ID wdCreate (void);
Differences from the VxWorks interface include:
Function Prototype:
#include <wdog.h>
STATUS wd_delete (WDOG_ID wdog);
Description: The wd_delete function will deallocate a watchdog. The watchdog will be removed from the timer queue if has been started.
Input Parameters:
Returned Values:
Assumptions/Limitations: It is the responsibility of the caller to assure that the watchdog is inactive before deleting it.
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the following comparable interface:
STATUS wdDelete (WDOG_ID wdog);
Differences from the VxWorks interface include:
Function Prototype:
#include <wdog.h>
STATUS wd_start( WDOG_ID wdog, int delay, wdentry_t wdentry,
intt argc, ....);
Description: This function adds a watchdog to the timer queue. The specified watchdog function will be called from the interrupt level after the specified number of ticks has elapsed. Watchdog timers may be started from the interrupt level.
Watchdog times execute in the context of the timer interrupt handler.
Watchdog timers execute only once.
To replace either the timeout delay or the function to be executed, call wd_start again with the same wdog; only the most recent wd_start() on a given watchdog ID has any effect.
Input Parameters:
Returned Values:
Assumptions/Limitations: The watchdog routine runs in the context of the timer interrupt handler and is subject to all ISR restrictions.
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the following comparable interface:
STATUS wdStart (WDOG_ID wdog, int delay, FUNCPTR wdentry, int parameter);
Differences from the VxWorks interface include:
Function Prototype:
#include <wdog.h>
STATUS wd_cancel (WDOG_ID wdog);
Description: This function cancels a currently running watchdog timer. Watchdog timers may be canceled from the interrupt level.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the following comparable interface:
STATUS wdCancel (WDOG_ID wdog);
Function Prototype:
#include <wdog.h>
Sint wd_gettime(WDOG_ID wdog);
Description: This function returns the time remaining before the the specified watchdog expires.
Input Parameters:
wdog. Identifies the watchdog that the request is for.Returned Value: The time in system ticks remaining until the watchdog time expires. Zero means either that wdog is not valid or that the wdog has already expired.
2.7 Clocks and Timers |
Function Prototype:
#include <time.h>
int clock_settime(clockid_t clockid, const struct timespec *tp);
Description:
Input Parameters:
parm. Returned Values:
If successful, the clock_settime() function will return zero (OK). Otherwise, an non-zero error number will be returned to indicate the error:
To be provided.Function Prototype:
#include <time.h>
int clock_gettime(clockid_t clockid, struct timespec *tp);
Description:
Input Parameters:
parm. Returned Values:
If successful, the clock_gettime() function will return zero (OK). Otherwise, an non-zero error number will be returned to indicate the error:
To be provided.Function Prototype:
#include <time.h>
int clock_getres(clockid_t clockid, struct timespec *res);
Description:
Input Parameters:
parm. Returned Values:
If successful, the clock_getres() function will return zero (OK). Otherwise, an non-zero error number will be returned to indicate the error:
To be provided.Function Prototype:
#include <time.h>
time_t mktime(struct tm *tp);
Description:
Input Parameters:
parm. Returned Values:
If successful, the mktime() function will return zero (OK). Otherwise, an non-zero error number will be returned to indicate the error:
To be provided.Function Prototype:
#include <time.h>
struct tm *gmtime_r(const time_t *clock, struct tm *result);
Description:
Input Parameters:
parm. Returned Values:
If successful, the gmtime_r() function will return zero (OK). Otherwise, an non-zero error number will be returned to indicate the error:
To be provided.
#include <time.h>
#define localtime_r(c,r) gmtime_r(c,r)
Function Prototype:
#include <time.h>
int timer_create(clockid_t clockid, struct sigevent *evp, timer_t *timerid);
Description:
The timer_create() function creates per-thread timer using the specified
clock, clock_id, as the timing base.
The timer_create() function returns, in
the location referenced by timerid, a timer ID of type timer_t used to identify
the timer in timer requests.
This timer ID is unique until the timer is deleted.
The particular clock, clock_id, is defined in <time.h>.
The timer whose ID is returned will be in a disarmed state upon return from
timer_create().
The evp argument, if non-NULL, points to a sigevent structure.
This structure is allocated by the called and defines the asynchronous notification to occur.
If the evp argument is NULL, the effect is as if the evp argument pointed to
a sigevent structure with the sigev_notify member having the value SIGEV_SIGNAL,
the sigev_signo having a default signal number, and the sigev_value member
having the value of the timer ID.
Each implementation defines a set of clocks that can be used as timing bases
for per-thread timers. All implementations shall support a clock_id of
CLOCK_REALTIME.
Input Parameters:
clockid. Specifies the clock to use as the timing base.
Must be CLOCK_REALTIME.evp. Refers to a user allocated sigevent structure that defines the
asynchronous notification. evp may be NULL (see above).timerid. The pre-thread timer created by the call to timer_create().Returned Values:
If the call succeeds, timer_create() will return 0 (OK) and update the
location referenced by timerid to a timer_t, which can be passed to the
other per-thread timer calls. If an error occurs, the function will return
a value of -1 (ERROR) and set errno to indicate the error.
EAGAIN. The system lacks sufficient signal queuing resources to honor the
request.EAGAIN. The calling process has already created all of the timers it is
allowed by this implementation.EINVAL. The specified clock ID is not defined.ENOTSUP. The implementation does not support the creation of a timer attached
to the CPU-time clock that is specified by clock_id and associated with a
thread different thread invoking timer_create().POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
CLOCK_REALTIME is supported for the clockid argument.Function Prototype:
#include <time.h>
int timer_delete(timer_t timerid);
Description:
The timer_delete() function deletes the specified timer, timerid, previously
created by the timer_create() function.
If the timer is armed when timer_delete() is called, the timer will be automatically disarmed before
removal.
The disposition of pending signals for the deleted timer is unspecified.
Input Parameters:
timerid.
The pre-thread timer, previously created by the call to timer_create(), to be deleted.Returned Values:
If successful, the timer_delete() function will return zero (OK).
Otherwise, the function will return a value of -1 (ERROR) and set
errno to indicate the error:
EINVAL. The timer specified timerid is not valid.POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <time.h>
int timer_settime(timer_t timerid, int flags, const struct itimerspec *value,
struct itimerspec *ovalue);
Description:
The timer_settime() function sets the time until the next expiration of the
timer specified by timerid from the it_value member of the value argument
and arm the timer if the it_value member of value is non-zero. If the
specified timer was already armed when timer_settime() is called, this call
will reset the time until next expiration to the value specified. If the
it_value member of value is zero, the timer will be disarmed. The effect
of disarming or resetting a timer with pending expiration notifications is
unspecified.
If the flag TIMER_ABSTIME is not set in the argument flags, timer_settime()
will behave as if the time until next expiration is set to be equal to the
interval specified by the it_value member of value. That is, the timer will
expire in it_value nanoseconds from when the call is made. If the flag
TIMER_ABSTIME is set in the argument flags, timer_settime() will behave as
if the time until next expiration is set to be equal to the difference between
the absolute time specified by the it_value member of value and the current
value of the clock associated with timerid. That is, the timer will expire
when the clock reaches the value specified by the it_value member of value.
If the specified time has already passed, the function will succeed and the
expiration notification will be made.
The reload value of the timer will be set to the value specified by the
it_interval member of value. When a timer is armed with a non-zero
it_interval, a periodic (or repetitive) timer is specified.
Time values that are between two consecutive non-negative integer multiples of the resolution of the specified timer will be rounded up to the larger multiple of the resolution. Quantization error will not cause the timer to expire earlier than the rounded time value.
If the argument ovalue is not NULL, the timer_settime() function will store,
in the location referenced by ovalue, a value representing the previous
amount of time before the timer would have expired, or zero if the timer was
disarmed, together with the previous timer reload value. Timers will not
expire before their scheduled time.
ovalue argument is ignored.
Input Parameters:
timerid. The pre-thread timer, previously created by the call to timer_create(), to be be set.flags. Specifie characteristics of the timer (see above)value. Specifies the timer value to setovalue. A location in which to return the time remaining from the previous timer setting (ignored).Returned Values:
If the timer_gettime() succeeds, a value of 0 (OK) will be returned.
If an error occurs, the value -1 (ERROR) will be returned, and
errno set to indicate the error.
EINVAL. The timerid argument does not correspond to an ID returned by timer_create() but not yet deleted by timer_delete().EINVAL. A value structure specified a nanosecond value less than zero or greater than or equal to 1000 million,
and the it_value member of that structure did not specify zero seconds and nanoseconds.POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
ovalue argument is ignored.Function Prototype:
#include <time.h>
int timer_gettime(timer_t timerid, struct itimerspec *value);
Description:
The timer_gettime() function will store the amount of time until the
specified timer, timerid, expires and the reload value of the timer into the
space pointed to by the value argument. The it_value member of this structure
will contain the amount of time before the timer expires, or zero if the timer
is disarmed. This value is returned as the interval until timer expiration,
even if the timer was armed with absolute time. The it_interval member of
value will contain the reload value last set by timer_settime().
Due to the asynchronous operation of this function, the time reported by this function could be significantly more than that actual time remaining on the timer at any time.
Input Parameters:
timerid. Specifies pre-thread timer, previously created by the call to
timer_create(), whose remaining count will be returned.Returned Values:
If successful, the timer_gettime() function will return zero (OK). Otherwise, an non-zero error number will be returned to indicate the error:
EINVAL.
The timerid argument does not correspond to an ID returned by
timer_create() but not yet deleted by timer_delete().POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <time.h>
int timer_getoverrun(timer_t timerid);
Description:
Only a single signal will be queued to the process for a given timer at any
point in time. When a timer for which a signal is still pending expires, no
signal will be queued, and a timer overrun will occur. When a timer
expiration signal is delivered to or accepted by a process, if the
implementation supports the Realtime Signals Extension, the
timer_getoverrun() function will return the timer expiration overrun count for
the specified timer. The overrun count returned contains the number of extra
timer expirations that occurred between the time the signal was generated
(queued) and when it was delivered or accepted, up to but not including an
implementation-defined maximum of DELAYTIMER_MAX. If the number of such
extra expirations is greater than or equal to DELAYTIMER_MAX, then the
overrun count will be set to DELAYTIMER_MAX. The value returned by
timer_getoverrun() will apply to the most recent expiration signal delivery
or acceptance for the timer. If no expiration signal has been delivered
for the timer, or if the Realtime Signals Extension is not supported, the
return value of timer_getoverrun() is unspecified.
NOTE: This interface is not currently implemented in NuttX.
Input Parameters:
timerid. Specifies pre-thread timer, previously created by the call to
timer_create(), whose overrun count will be returned.
Returned Values:
If the timer_getoverrun() function succeeds, it will return the timer
expiration overrun count as explained above. timer_getoverrun() will fail if:
EINVAL.
The timerid argument does not correspond to an ID returned by
timer_create() but not yet deleted by timer_delete().POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
2.8 Signal Interfaces |
NuttX provides signal interfaces for tasks. Signals are used to alter the flow control of tasks by communicating asynchronous events within or between task contexts. Any task or interrupt handler can post (or send) a signal to a particular task. The task being signaled will execute task-specified signal handler function the next time that the task has priority. The signal handler is a user-supplied function that is bound to a specific signal and performs whatever actions are necessary whenever the signal is received.
There are no predefined actions for any signal. The default action for all signals (i.e., when no signal handler has been supplied by the user) is to ignore the signal. In this sense, all NuttX are real time signals.
Tasks may also suspend themselves and wait until a signal is received.
The following signal handling interfaces are provided by NuttX:
Function Prototype:
#include <signal.h>
int sigemptyset(sigset_t *set);
Description: This function initializes the signal set specified by set such that all signals are excluded.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <signal.h>
int sigfillset(sigset_t *set);
Description: This function initializes the signal set specified by set such that all signals are included.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <signal.h>
int sigaddset(sigset_t *set, int signo);
Description: This function adds the signal specified by signo to the signal set specified by set.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <signal.h>
int sigdelset(sigset_t *set, int signo);
Description: This function deletes the signal specified by signo from the signal set specified by set.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <signal.h>
int sigismember(const sigset_t *set, int signo);
Description: This function tests whether the signal specified by signo is a member of the set specified by set.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <signal.h>
int sigaction( int signo, const struct sigaction *act,
struct sigaction *oact );
Description: This function allows the calling task to examine and/or specify the action to be associated with a specific signal.
The structure sigaction, used to describe an action to be taken, is defined to include the following members:
If the argument act is not NULL, it points to a structure specifying the action to be associated with the specified signal. If the argument oact is not NULL, the action previously associated with the signal is stored in the location pointed to by the argument oact. If the argument act is NULL, signal handling is unchanged by this function call; thus, the call can be used to enquire about the current handling of a given signal.
When a signal is caught by a signal-catching function installed by the sigaction() function, a new signal mask is calculated and installed for the duration of the signal-catching function. This mask is formed by taking the union of the current signal mask and the value of the sa_mask for the signal being delivered, and then including the signal being delivered. If and when the signal handler returns, the original signal mask is restored.
Signal catching functions execute in the same address environment as the task that called sigaction() to install the signal-catching function.
Once an action is installed for a specific signal, it remains installed until another action is explicitly requested by another call to sigaction().
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the POSIX implementation include:
Function Prototype:
#include <signal.h>
int sigprocmask(int how, const sigset_t *set, sigset_t *oset);
Description: This function allows the calling task to examine and/or change its signal mask. If the set is not NULL, then it points to a set of signals to be used to change the currently blocked set. The value of how indicates the manner in which the set is changed.
If there are any pending unblocked signals after the call to sigprocmask(), those signals will be delivered before sigprocmask() returns.
If sigprocmask() fails, the signal mask of the task is not changed.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <signal.h>
int sigpending( sigset_t *set );
Description: This function stores the returns the set of signals that are blocked for delivery and that are pending for the calling task in the space pointed to by set.
If the task receiving a signal has the signal blocked via its sigprocmask, the signal will pend until it is unmasked. Only one pending signal (for a given signo) is retained by the system. This is consistent with POSIX which states: "If a subsequent occurrence of a pending signal is generated, it is implementation defined as to whether the signal is delivered more than once."
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <signal.h>
int sigsuspend( const sigset_t *set );
Description: The sigsuspend() function replaces the signal mask with the set of signals pointed to by the argument set and then suspends the task until delivery of a signal to the task.
If the effect of the set argument is to unblock a pending signal, then no wait is performed.
The original signal mask is restored when sigsuspend() returns.
Waiting for an empty signal set stops a task without freeing any resources (a very bad idea).
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the POSIX specification include:
Function Prototype:
#include <signal.h>
int sigwaitinfo(const sigset_t *set, struct siginfo *info);
Description: This function is equivalent to sigtimedwait() with a NULL timeout parameter. (see below).
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <signal.h>
int sigtimedwait( const sigset_t *set, struct siginfo *info,
const struct timespec *timeout );
Description: This function selects the pending signal set specified by the argument set. If multiple signals are pending in set, it will remove and return the lowest numbered one. If no signals in set are pending at the time of the call, the calling task will be suspended until one of the signals in set becomes pending OR until the task interrupted by an unblocked signal OR until the time interval specified by timeout (if any), has expired. If timeout is NULL, then the timeout interval is forever.
If the info argument is non-NULL, the selected signal number is stored in the si_signo member and the cause of the signal is store in the si_code member. The content of si_value is only meaningful if the signal was generated by sigqueue(). The following values for si_code are defined in signal.h:
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the POSIX interface include:
Function Prototype:
#include <signal.h>
int sigqueue (int tid, int signo, union sigval value);
Description: This function sends the signal specified by signo with the signal parameter value to the task specified by tid.
If the receiving task has the signal blocked via its sigprocmask, the signal will pend until it is unmasked. Only one pending signal (for a given signo) is retained by the system. This is consistent with POSIX which states: "If a subsequent occurrence of a pending signal is generated, it is implementation defined as to whether the signal is delivered more than once."
Input Parameters:
Returned Values:
errno is set appropriately.
EGAIN. The limit of signals which may be queued has been reached.EINVAL. signo was invalid.EPERM. The task does not have permission to send the signal to the receiving process.ESRCH. No process has a PID matching pid.Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the POSIX interface include:
Function Prototype:
#include <sys/types.h> #include <signal.h> int kill(pid_t pid, int sig);
Description: The kill() system call can be used to send any signal to any task.
If the receiving task has the signal blocked via its sigprocmask, the signal will pend until it is unmasked. Only one pending signal (for a given signo) is retained by the system. This is consistent with POSIX which states: "If a subsequent occurrence of a pending signal is generated, it is implementation defined as to whether the signal is delivered more than once."
Input Parameters:
kill() specification encodes process group
information as zero and negative pid values.
Only positive, non-zero values of pid are supported by this
implementation. ID of the task to receive signal
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Differences from the POSIX interface include:
2.9 Pthread Interfaces |
NuttX does not support processes in the way that, say, Linux does. NuttX only supports simple threads or tasks running within the same address space. For the most part, threads and tasks are interchangeable and differ primarily only in such things as the inheritance of file descriptors. Basically, threads are initialized and uninitialized differently and share a few more resources than tasks.
The following pthread interfaces are supported in some form by NuttX:
No support for the following pthread interfaces is provided by NuttX:
pthread_atfork. register fork handlers.pthread_attr_getdetachstate. get and set the detachstate attribute.pthread_attr_getguardsize. get and set the thread guardsize attribute.pthread_attr_getinheritsched. get and set the inheritsched attribute.pthread_attr_getscope. get and set the contentionscope attribute.pthread_attr_getstack. get and set stack attributes.pthread_attr_getstackaddr. get and set the stackaddr attribute.pthread_attr_setdetachstate. get and set the detachstate attribute.pthread_attr_setguardsize. get and set the thread guardsize attribute.pthread_attr_setscope. get and set the contentionscope attribute.pthread_attr_setstack. get and set stack attributes.pthread_attr_setstackaddr. get and set the stackaddr attribute.pthread_barrier_destroy. destroy and initialize a barrier object.pthread_barrier_init. destroy and initialize a barrier object.pthread_barrier_wait. synchronize at a barrier.pthread_cleanup_pop. establish cancellation handlers.pthread_cleanup_push. establish cancellation handlers.pthread_condattr_getclock. set the clock selection condition variable attribute.pthread_condattr_getpshared. get the process-shared condition variable attribute.pthread_condattr_setclock. set the clock selection condition variable attribute.pthread_condattr_setpshared. set the process-shared condition variable attribute.pthread_getconcurrency. get and set the level of concurrency.pthread_getcpuclockid. access a thread CPU-time clock.pthread_mutex_getprioceiling. get and set the priority ceiling of a mutex.pthread_mutex_setprioceiling. get and set the priority ceiling of a mutex.pthread_mutex_timedlock. lock a mutex.pthread_mutexattr_getprioceiling. get and set the prioceiling attribute of the mutex attributes object.pthread_mutexattr_getprotocol. get and set the protocol attribute of the mutex attributes object.pthread_mutexattr_setprioceiling. get and set the prioceiling attribute of the mutex attributes object.pthread_mutexattr_setprotocol. get and set the protocol attribute of the mutex attributes object.pthread_rwlock_destroy. destroy and initialize a read-write lock object.pthread_rwlock_init. destroy and initialize a read-write lock object.pthread_rwlock_rdlock. lock a read-write lock object for reading.pthread_rwlock_timedrdlock. lock a read-write lock for reading.pthread_rwlock_timedwrlock. lock a read-write lock for writing.pthread_rwlock_tryrdlock. lock a read-write lock object for reading.pthread_rwlock_trywrlock. lock a read-write lock object for writing.pthread_rwlock_unlock. unlock a read-write lock object.pthread_rwlock_wrlock. lock a read-write lock object for writing.pthread_rwlockattr_destroy. destroy and initialize the read-write lock attributes object.pthread_rwlockattr_getpshared. get and set the process-shared attribute of the read-write lock attributes object.pthread_rwlockattr_init. destroy and initialize the read-write lock attributes object.pthread_rwlockattr_setpshared. get and set the process-shared attribute of the read-write lock attributes object.pthread_setcanceltype. set cancelability state.pthread_setconcurrency. get and set the level of concurrency.pthread_spin_destroy. destroy or initialize a spin lock object.pthread_spin_init. destroy or initialize a spin lock object.pthread_spin_lock. lock a spin lock object.pthread_spin_trylock. lock a spin lock object.pthread_spin_unlock. unlock a spin lock object.pthread_testcancel. set cancelability state.Function Prototype:
#include <pthread.h>
int pthread_attr_init(pthread_attr_t *attr);
Description: Initializes a thread attributes object (attr) with default values for all of the individual attributes used by the implementation.
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_attr_init() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_attr_destroy(pthread_attr_t *attr);
Description: An attributes object can be deleted when it is no longer needed.
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_attr_destroy() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_attr_setschedpolicy() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_attr_getschedpolicy(pthread_attr_t *attr, int *policy);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_attr_getschedpolicy() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_attr_setschedparam(pthread_attr_t *attr,
const struct sched_param *param);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_attr_getschedpolicy() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_attr_getschedparam(pthread_attr_t *attr,
struct sched_param *param);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_attr_getschedparam() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_attr_setinheritsched(pthread_attr_t *attr,
int inheritsched);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_attr_setinheritsched() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_attr_getinheritsched(const pthread_attr_t *attr,
int *inheritsched);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_attr_getinheritsched() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_attr_setstacksize(pthread_attr_t *attr, long stacksize);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_attr_setstacksize() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_attr_getstacksize(pthread_attr_t *attr, long *stackaddr);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_attr_getstacksize() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_create(pthread_t *thread, pthread_attr_t *attr,
pthread_startroutine_t startRoutine,
pthread_addr_t arg);
Description: To create a thread object and runnable thread, a routine must be specified as the new thread's start routine. An argument may be passed to this routine, as an untyped address; an untyped address may also be returned as the routine's value. An attributes object may be used to specify details about the kind of thread being created.
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_create() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_detach(pthread_t thread);
Description: A thread object may be "detached" to specify that the return value and completion status will not be requested.
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_detach() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
void pthread_exit(pthread_addr_t pvValue);
Description: A thread may terminate it's own execution.
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_exit() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_cancel(pthread_t thread);
Description:
The pthread_cancel() function shall request that thread be canceled. The target thread's cancelability state determines when the cancellation takes effect. When the cancellation is acted on, thread shall be terminated.
When cancelability is disabled, all cancels are held pending in the target thread until the thread changes the cancelability. When cancelability is deferred, all cancels are held pending in the target thread until the thread changes the cancelability or calls pthread_testcancel().
Cancelability is asynchronous; all cancels are acted upon immediately (when enable), interrupting the thread with its processing.
Input Parameters:
Returned Values:
If successful, the ptnread_cancel() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
POSIX Compatibility: Comparable to the POSIX interface of the same name. Except:
Function Prototype:
#include <pthread.h>
int pthread_setcancelstate(int state, int *oldstate);
Description:
The pthread_setcancelstate() function atomically sets both the calling thread's cancelability state to the indicated state and returns the previous cancelability state at the location referenced by oldstate. Legal values for state are PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DISABLE.<.li>
Any pending thread cancelation may occur at the time that the cancelation state is set to PTHREAD_CANCEL_ENABLE.
Input Parameters:
Returned Values:
If successful, the pthread_setcancelstate() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_setcancelstate(void);
Description:
NOT SUPPORTED Input Parameters:
To be provided.Returned Values:
If successful, the pthread_setcancelstate() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_join(pthread_t thread, pthread_addr_t *ppvValue);
Description: A thread can await termination of another thread and retrieve the return value of the thread.
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_join() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
void pthread_yield(void);
Description: A thread may tell the scheduler that its processor can be made available.
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_yield() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
pthread_t pthread_self(void);
Description: A thread may obtain a copy of its own thread handle.
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_self() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_getschedparam(pthread_t thread, int *policy,
struct sched_param *param);
Description:
The pthread_getschedparam() functions will get the
scheduling policy and parameters of threads.
For SCHED_FIFO and SCHED_RR, the only
required member of the sched_param structure is the
priority sched_priority.
The pthread_getschedparam() function will retrieve the
scheduling policy and scheduling parameters for the thread whose thread
ID is given by thread and will store those values in
policy and param, respectively.
The priority value returned from pthread_getschedparam()
will be the value specified by the most recent pthread_setschedparam(),
pthread_setschedprio(), or pthread_create() call
affecting the target thread.
It will not reflect any temporary adjustments to its priority (such as might
result of any priority inheritance, for example).
The policy parameter may have the value SCHED_FIFO or SCHED_RR
(SCHED_OTHER and SCHED_SPORADIC, in particular, are not supported).
The SCHED_FIFO and SCHED_RR policies will have a single
scheduling parameter, sched_priority.
Input Parameters:
thread.
The ID of thread whose scheduling parameters will be queried.
policy.
The location to store the thread's scheduling policy.
param.
The location to store the thread's priority.
Returned Values:
0 (OK) if successful.
Otherwise, the error code ESRCH if the value specified by
thread does not refer to an existing thread.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_setschedparam(pthread_t thread, int policy,
const struct sched_param *param);
Description:
The pthread_setschedparam() functions will set the scheduling policy
and parameters of threads.
For SCHED_FIFO and SCHED_RR, the only required member
of the sched_param structure is the priority sched_priority.
pthread_setschedparam() function will set the scheduling policy
and associated scheduling parameters for the thread whose thread ID is given by
thread to the policy and associated parameters provided in
policy and param, respectively.
The policy parameter may have the value SCHED_FIFO or SCHED_RR.
(SCHED_OTHER and SCHED_SPORADIC, in particular, are not supported).
The SCHED_FIFO and SCHED_RR policies will have a single
scheduling parameter, sched_priority.
If the pthread_setschedparam() function fails, the scheduling
parameters will not be changed for the target thread.
Input Parameters:
thread.
The ID of thread whose scheduling parameters will be modified.
policy.
The new scheduling policy of the thread.
Either SCHED_FIFO or SCHED_RR.
SCHED_OTHER and SCHED_SPORADIC are not supported.
param.
The location to store the thread's priority.
Returned Values:
If successful, the pthread_setschedparam() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
EINVAL.
The value specified by policy or one of the scheduling parameters
associated with the scheduling policy policy is invalid.
ENOTSUP.
An attempt was made to set the policy or scheduling parameters to an unsupported
value (SCHED_OTHER and SCHED_SPORADIC in particular are
not supported)
EPERM.
The caller does not have the appropriate permission to set either the scheduling
parameters or the scheduling policy of the specified thread.
Or, the implementation does not allow the application to modify one of the
parameters to the value specified.
ESRCH.
The value specified by thread does not refer to a existing thread.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_key_create( pthread_key_t *key, void (*destructor)(void*) )
Description:
This function creates a thread-specific data key visible to all threads in the system. Although the same key value may be used by different threads, the values bound to the key by pthread_setspecific() are maintained on a per-thread basis and persist for the life of the calling thread.
Upon key creation, the value NULL will be associated with the the new key in all active threads. Upon thread creation, the value NULL will be associated with all defined keys in the new thread.
Input Parameters:
Returned Values:
If successful, the pthread_key_create() function will store the newly created key value at *key and return zero (OK). Otherwise, an error number will be returned to indicate the error:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_setspecific( pthread_key_t key, void *value )
Description:
The pthread_setspecific() function associates a thread- specific value with a key obtained via a previous call to pthread_key_create(). Different threads may bind different values to the same key. These values are typically pointers to blocks of dynamically allocated memory that have been reserved for use by the calling thread.
The effect of calling pthread_setspecific() with a key value not obtained from pthread_key_create() or after a key has been deleted with pthread_key_delete() is undefined.
Input Parameters:
Returned Values:
If successful, pthread_setspecific() will return zero (OK). Otherwise, an error number will be returned:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
void *pthread_getspecific( pthread_key_t key )
Description:
The pthread_getspecific() function returns the value currently bound to the specified key on behalf of the calling thread.
The effect of calling pthread_getspecific() with a key value not obtained from pthread_key_create() or after a key has been deleted with pthread_key_delete() is undefined.
Input Parameters:
Returned Values:
The function pthread_getspecific() returns the thread- specific data associated with the given key. If no thread specific data is associated with the key, then the value NULL is returned.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_key_delete( pthread_key_t key )
Description:
This POSIX function should delete a thread-specific data key previously returned by pthread_key_create(). However, this function does nothing in the present implementation.
Input Parameters:
Returned Values:
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_mutexattr_init(pthread_mutexattr_t *attr);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_mutexattr_init() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Protoype:
#include <pthread.h>
int pthread_mutexattr_destroy(pthread_mutexattr_t *attr);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_mutexattr_destroy() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_mutexattr_getpshared(pthread_mutexattr_t *attr,
int *pshared);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_mutexattr_getpshared() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr,
int pshared);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_mutexattr_setpshared() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
#ifdef CONFIG_MUTEX_TYPES
int pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *type);
#endif
Description: Return the mutex type from the mutex attributes.
Input Parameters:
attr. The mutex attributes to querytype. Location to return the mutex type. See
pthread_mutexattr_setttyp()
for a description of possible mutex types that may be returned.Returned Values:
If successful, the pthread_mutexattr_settype() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
EINVAL. Parameters attr and/or attr are invalid.POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
#ifdef CONFIG_MUTEX_TYPES
int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type);
#endif
Description: Set the mutex type in the mutex attributes.
Input Parameters:
attr. The mutex attributes in which to set the mutex type.type. The mutex type value to set. The following values are supported:
PTHREAD_MUTEX_NORMAL. This type of mutex does not detect deadlock. A thread
attempting to relock this mutex without first unlocking it will deadlock.
Attempting to unlock a mutex locked by a different thread results in undefined
behavior. Attempting to unlock an unlocked mutex results in undefined behavior. PTHREAD_MUTEX_ERRORCHECK. This type of mutex provides error checking.
A thread attempting to relock this mutex without first unlocking it will return with an error.
A thread attempting to unlock a mutex which another thread has locked will return with an error.
A thread attempting to unlock an unlocked mutex will return with an error.PTHREAD_MUTEX_RECURSIVE. A thread attempting to relock this mutex without first
unlocking it will succeed in locking the mutex. The relocking deadlock which can occur with mutexes
of type PTHREAD_MUTEX_NORMAL cannot occur with this type of mutex. Multiple locks of this mutex
require the same number of unlocks to release the mutex before another thread can acquire the mutex.
A thread attempting to unlock a mutex which another thread has locked will return with an error.
A thread attempting to unlock an unlocked mutex will return with an error.PTHREAD_MUTEX_DEFAULT. The default mutex type (PTHREAD_MUTEX_NORMAL).
In NuttX, PTHREAD_MUTEX_NORMAL is not implemented. Rather, the behavior described
for PTHREAD_MUTEX_ERRORCHECK is the normal behavior.
Returned Values:
If successful, the pthread_mutexattr_settype() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
EINVAL. Parameters attr and/or attr are invalid.POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_mutex_init(pthread_mutex_t *mutex,
pthread_mutexattr_t *attr);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_mutex_init() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_mutex_destroy(pthread_mutex_t *mutex);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_mutex_destroy() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_mutex_lock(pthread_mutex_t *mutex);
Description:
The mutex object referenced by mutex is locked by calling pthread_mutex_lock().
If the mutex is already locked, the calling thread blocks until the mutex
becomes available. This operation returns with the mutex object referenced
by mutex in the locked state with the calling thread as its owner.
If the mutex type is PTHREAD_MUTEX_NORMAL, deadlock detection is not provided.
Attempting to relock the mutex causes deadlock. If a thread attempts to unlock
a mutex that it has not locked or a mutex which is unlocked, undefined behavior
results.
In NuttX, PTHREAD_MUTEX_NORMAL is not implemented. Rather, the behavior described
for PTHREAD_MUTEX_ERRORCHECK is the normal behavior.
If the mutex type is PTHREAD_MUTEX_ERRORCHECK, then error checking is provided.
If a thread attempts to relock a mutex that it has already locked, an error
will be returned. If a thread attempts to unlock a mutex that it has not
locked or a mutex which is unlocked, an error will be returned.
If the mutex type is PTHREAD_MUTEX_RECURSIVE, then the mutex maintains the concept
of a lock count. When a thread successfully acquires a mutex for the first time,
the lock count is set to one. Every time a thread relocks this mutex, the lock count
is incremented by one. Each time the thread unlocks the mutex, the lock count is
decremented by one. When the lock count reaches zero, the mutex becomes available
for other threads to acquire. If a thread attempts to unlock a mutex that it has
not locked or a mutex which is unlocked, an error will be returned.
If a signal is delivered to a thread waiting for a mutex, upon return from the signal handler the thread resumes waiting for the mutex as if it was not interrupted.
Input Parameters:
mutex. A reference to the mutex to be locked.Returned Values:
If successful, the pthread_mutex_lock() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. Note that this function will never return the error EINTR.
Assumptions/Limitations:POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_mutex_trylock(pthread_mutex_t *mutex);
Description:
The function pthread_mutex_trylock() is identical to pthread_mutex_lock()
except that if the mutex object referenced by mutex is currently locked
(by any thread, including the current thread), the call returns immediately
with the errno EBUSY.
If a signal is delivered to a thread waiting for a mutex, upon return from the signal handler the thread resumes waiting for the mutex as if it was not interrupted.
Input Parameters:
mutex. A reference to the mutex to be locked.Returned Values:
If successful, the pthread_mutex_trylock() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. Note that this function will never return the error EINTR.
Assumptions/Limitations:POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_mutex_unlock(pthread_mutex_t *mutex);
Description:
The pthread_mutex_unlock() function releases the mutex object referenced
by mutex. The manner in which a mutex is released is dependent upon the
mutex's type attribute. If there are threads blocked on the mutex object
referenced by mutex when pthread_mutex_unlock() is called, resulting in
the mutex becoming available, the scheduling policy is used to determine
which thread shall acquire the mutex. (In the case of PTHREAD_MUTEX_RECURSIVE
mutexes, the mutex becomes available when the count reaches zero and the
calling thread no longer has any locks on this mutex).
If a signal is delivered to a thread waiting for a mutex, upon return from the signal handler the thread resumes waiting for the mutex as if it was not interrupted.
Input Parameters:
param.Returned Values:
If successful, the pthread_mutex_unlock() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. Note that this function will never return the error EINTR.
Assumptions/Limitations:POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_condattr_init(pthread_condattr_t *attr);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_condattr_init() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_condattr_destroy(pthread_condattr_t *attr);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_condattr_destroy() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *attr);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_cond_init() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_cond_destroy(pthread_cond_t *cond);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_cond_destroy() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_cond_broadcast(pthread_cond_t *cond);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_cond_broadcast() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_cond_signal(pthread_cond_t *dond);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_cond_signal() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_cond_wait() function will return zero (OK). Otherwise, an error number will be returned to indicate the error:
To be provided. POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
const struct timespec *abstime);
Description:
Input Parameters:
To be provided.Returned Values:
If successful, the pthread_cond_timedwait() function will return
zero (OK). Otherwise, an error number will be
returned to indicate the error:
To be provided. Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_barrierattr_init(FAR pthread_barrierattr_t *attr);
Description:
The pthread_barrierattr_init() function will initialize a barrier
attribute object attr with the default value for all of the attributes
defined by the implementation.
Input Parameters:
attr. Barrier attributes to be initialized.
Returned Values:
0 (OK) on success or EINVAL if attr is invalid.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_barrierattr_destroy(FAR pthread_barrierattr_t *attr);
Description:
The pthread_barrierattr_destroy() function will destroy a barrier attributes object.
A destroyed attributes object can be reinitialized using pthread_barrierattr_init();
the results of otherwise referencing the object after it has been destroyed are undefined.
Input Parameters:
attr. Barrier attributes to be destroyed.
Returned Values: 0 (OK) on success or EINVAL if attr is invalid.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_barrierattr_setpshared(FAR pthread_barrierattr_t *attr, int pshared);
Description:
The process-shared attribute is set to PTHREAD_PROCESS_SHARED to permit
a barrier to be operated upon by any thread that has access to the memory where the
barrier is allocated.
If the process-shared attribute is PTHREAD_PROCESS_PRIVATE, the barrier can
only be operated upon by threads created within the same process as the thread that
initialized the barrier.
If threads of different processes attempt to operate on such a barrier, the behavior is undefined.
The default value of the attribute is PTHREAD_PROCESS_PRIVATE.
Input Parameters:
attr. Barrier attributes to be modified.pshared. The new value of the pshared attribute.
Returned Values: 0 (OK) on success or EINVAL if either
attr is invalid or pshared is not one of
PTHREAD_PROCESS_SHARED or PTHREAD_PROCESS_PRIVATE.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_barrierattr_getpshared(FAR const pthread_barrierattr_t *attr, FAR int *pshared);
Description:
The pthread_barrierattr_getpshared() function will obtain the value of the
process-shared attribute from the attributes object referenced by attr.
Input Parameters:
attr. Barrier attributes to be queried.pshared. The location to stored the current value of the pshared attribute.
Returned Values: 0 (OK) on success or EINVAL if
either attr or pshared is invalid.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_barrier_init(FAR pthread_barrier_t *barrier,
FAR const pthread_barrierattr_t *attr, unsigned int count);
Description:
The pthread_barrier_init() function allocates any resources required to
use the barrier referenced by barrier and initialized the barrier with
the attributes referenced by attr.
If attr is NULL, the default barrier attributes will be used.
The results are undefined if pthread_barrier_init() is called when any
thread is blocked on the barrier.
The results are undefined if a barrier is used without first being initialized.
The results are undefined if pthread_barrier_init() is called specifying
an already initialized barrier.
Input Parameters:
barrier.
The barrier to be initialized.
attr.
Barrier attributes to be used in the initialization.
count.
The count to be associated with the barrier.
The count argument specifies the number of threads that must call
pthread_barrier_wait() before any of them successfully return from the call.
The value specified by count must be greater than zero.
Returned Values:0 (OK) on success or on of the following error numbers:
EAGAIN.
The system lacks the necessary resources to initialize another barrier.
EINVAL.
The barrier reference is invalid, or the values specified by attr are invalid, or
the value specified by count is equal to zero.
ENOMEM.
Insufficient memory exists to initialize the barrier.
EBUSY.
The implementation has detected an attempt to reinitialize a barrier while it is in use.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_barrier_destroy(FAR pthread_barrier_t *barrier);
Description:
The pthread_barrier_destroy() function destroys the barrier referenced
by barrie and releases any resources used by the barrier.
The effect of subsequent use of the barrier is undefined until the barrier is
reinitialized by another call to pthread_barrier_init().
The results are undefined if pthread_barrier_destroy() is called when
any thread is blocked on the barrier, or if this function is called with an
uninitialized barrier.
Input Parameters:
barrier. The barrier to be destroyed.
Returned Values: 0 (OK) on success or on of the following error numbers:
EBUSY.
The implementation has detected an attempt to destroy a barrier while it is in use.
EINVAL.
The value specified by barrier is invalid.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_barrier_wait(FAR pthread_barrier_t *barrier);
Description:
The pthread_barrier_wait() function synchronizse participating
threads at the barrier referenced by barrier.
The calling thread is blocked until the required number of threads have called
pthread_barrier_wait() specifying the same barrier.
When the required number of threads have called pthread_barrier_wait()
specifying the barrier, the constant PTHREAD_BARRIER_SERIAL_THREAD
will be returned to one unspecified thread and zero will be returned to each of
the remaining threads.
At this point, the barrier will be reset to the state it had as a result of the most
recent pthread_barrier_init() function that referenced it.
The constant PTHREAD_BARRIER_SERIAL_THREAD is defined in
pthread.h and its value must be distinct from any other value
returned by pthread_barrier_wait().
The results are undefined if this function is called with an uninitialized barrier.
If a signal is delivered to a thread blocked on a barrier, upon return from the signal handler the thread will resume waiting at the barrier if the barrier wait has not completed. Otherwise, the thread will continue as normal from the completed barrier wait. Until the thread in the signal handler returns from it, it is unspecified whether other threads may proceed past the barrier once they have all reached it.
A thread that has blocked on a barrier will not prevent any unblocked thread that is eligible to use the same processing resources from eventually making forward progress in its execution. Eligibility for processing resources will be determined by the scheduling policy.
Input Parameters:
barrier. The barrier on which to wait.
Returned Values: 0 (OK) on success or EINVAL if the barrier is not valid.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <pthread.h>
int pthread_once(FAR pthread_once_t *once_control, CODE void (*init_routine)(void));
Description:
The first call to pthread_once() by any thread with a given
once_control, will call the init_routine() with no arguments.
Subsequent calls to pthread_once() with the same once_control will have no effect.
On return from pthread_once(), init_routine() will have completed.
Input Parameters:
once_control.
Determines if init_routine() should be called.
once_control should be declared and intialized as follows:
pthread_once_t once_control = PTHREAD_ONCE_INIT;
PTHREAD_ONCE_INIT is defined in pthread.h.
init_routine.
The initialization routine that will be called once.
Returned Values: 0 (OK) on success or EINVAL if either once_control or init_routine are invalid.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <signal.h>
#include <pthread.h>
int pthread_kill(pthread_t thread, int signo)
Description:
The pthread_kill() system call can be used to send any
signal to a thread. See kill() for further information
as this is just a simple wrapper around the kill()
function.
Input Parameters:
thread.
The id of the thread to receive the signal. Only positive, non-zero values of tthreadt are supported.
signo.
The signal number to send. If signo is zero, no signal is sent, but all error checking is performed.
Returned Values:
On success, the signal was sent and zero is returned. On error one of the following error numbers is returned.
EINVAL.
An invalid signal was specified.
EPERM.
The thread does not have permission to send the signal to the target thread.
ESRCH.
No thread could be found corresponding to that specified by the given thread ID.
ENOSYS.
Do not support sending signals to process groups.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
Function Prototype:
#include <signal.h>
#include <pthread.h>
int pthread_sigmask(int how, FAR const sigset_t *set, FAR sigset_t *oset);
Description:
This function is a simple wrapper around sigprocmask().
See the sigprocmask() function description for further information.
Input Parameters:
how. How the signal mast will be changed:
SIG_BLOCK:
The resulting set is the union of the current set and the signal set pointed to by set.
SIG_UNBLOCK:
The resulting set is the intersection of the current set and the complement of the signal set pointed to by set.
SIG_SETMASK:
The resulting set is the signal set pointed to by set.
set. Location of the new signal mask.
oset. Location to store the old signal mask.
Returned Values:
0 (OK) on succes or EINVAL if how is invalid.
Assumptions/Limitations:
POSIX Compatibility: Comparable to the POSIX interface of the same name.
2.10 Environment Variables |
Overview. NuttX supports environment variables that can be used to control the behavior of programs. In the spirit of NuttX the environment variable behavior attempts to emulate the behavior of environment variables in the mulit-processing OS:
Programming Interfaces. The following environment variable programming interfaces are provided by Nuttx and are described in detail in the following paragraphs.
Disabling Environment Variable Support.
All support for environment variables can be disabled by setting CONFIG_DISABLE_ENVIRON
in the board configuration file.
getenvFunction Prototype:
#include <stdlib.h> FAR char *getenv(const char *name);
Description:
The getenv() function searches the environment list for a string that
matches the string pointed to by name.
Input Parameters:
name.
The name of the variable to find.
Returned Values: The value of the valiable (read-only) or NULL on failure.
putenvFunction Prototype:
#include <stdlib.h> int putenv(char *string);
Description:
The putenv() function adds or changes the value of environment variables.
The argument string is of the form name=value. If name does not already
exist in the environment, then string is added to the environment. If
name does exist, then the value of name in the environment is changed to
value.
Input Parameters:
string
name=value string describing the environment setting to add/modify.
Returned Values: Zero on sucess.
clearenvFunction Prototype:
#include <stdlib.h> int clearenv(void);
Description:
The clearenv() function clears the environment of all name-value pairs
and sets the value of the external variable environ to NULL.
Input Parameters: None
Returned Values: Zero on success.
setenvFunction Prototype:
#include <stdlib.h> int setenv(const char *name, const char *value, int overwrite);
Description:
The setenv() function adds the variable name to the environment with the
specified value if the variable name does not exist. If the name
does exist in the environment, then its value is changed to value if overwrite
is non-zero; if overwrite is zero, then the value of name is unaltered.
Input Parameters:
name
The name of the variable to change.
value
The new value of the variable.
value
Replace any existing value if non-zero.
Returned Values: Zero on success.
unsetenvFunction Prototype:
#include <stdlib.h> int unsetenv(const char *name);
Description:
The unsetenv() function deletes the variable name from the environment.
Input Parameters:
name
The name of the variable to delete.
Returned Values: Zero on success.
2.11 File System Interfaces |
mmap() and eXecute In Place (XIP)Overview. NuttX includes an optional, scalable file system. This file-system may be omitted altogther; NuttX does not depend on the presence of any file system.
Pseudo Root File System.
Or, a simple in-memory, psuedo file system can be enabled.
This simple file system can be enabled setting the CONFIG_NFILE_DESCRIPTORS
option to a non-zero value.
This is an in-memory file system because it does not require any
storage medium or block driver support.
Rather, file system contents are generated on-the-fly as referenced via
standard file system operations (open, close, read, write, etc.).
In this sense, the file system is psuedo file system (in the
same sense that the Linux /proc file system is also
referred to as a psuedo file system).
Any user supplied data or logic can be accessed via the psuedo-file system.
Built in support is provided for character and block drivers in the
/dev psuedo file system directory.
Mounted File Systems
The simple in-memory file system can be extended my mounting block
devices that provide access to true file systems backed up via some
mass storage device.
NuttX supports the standard mount() command that allows
a block driver to be bound to a mountpoint within the psuedo file system
and to a a file system.
At present, NuttX supports only the VFAT file system.
Comparison to Linux From a programming perspective, the NuttX file system appears very similar to a Linux file system. However, there is a fundamental difference: The NuttX root file system is a psuedo file system and true file systems may be mounted in the psuedo file system. In the typical Linux installation by comparison, the Linux root file system is a true file system and psuedo file systems may be mounted in the true, root file system. The approach selected by NuttX is intended to support greater scalability from the very tiny platform to the moderate platform.
File System Interfaces.
The NuttX file system simply supports a set of standard, file system APIs
(open(), close(), read(), write, etc.)
and a registration mechanism that allows devices drivers to a associated with nodes
in a file-system-like name space.
#include <fcntl.h> int open(const char *path, int oflag, ...);
#include <unistd.h> int close(int fd); int dup(int fildes); int dup2(int fildes1, int fildes2); off_t lseek(int fd, off_t offset, int whence); ssize_t read(int fd, void *buf, size_t nbytes); int unlink(const char *path); ssize_t write(int fd, const void *buf, size_t nbytes);
#include <sys/ioctl.h> int ioctl(int fd, int req, unsigned long arg);
Function Prototype:
#include <poll.h> int poll(struct pollfd *fds, nfds_t nfds, int timeout);
Description:
poll() waits for one of a set of file descriptors to become ready to
perform I/O. If none of the events requested (and no error) has
occurred for any of the file descriptors, then poll() blocks until
one of the events occurs.
Configuration Settings.
In order to use the poll() API, the following must be defined
in your NuttX configuration file:
CONFIG_NFILE_DESCRIPTORS Defined to be greater than 0CONFIG_DISABLE_POLL NOT definedIn order to use the select with TCP/IP sockets test, you must also have the following additional things selected in your NuttX configuration file:
CONFIG_NET Defined for general network supportCONFIG_NET_TCP Defined for TCP/IP supportCONFIG_NSOCKET_DESCRIPTORS Defined to be greater than 0CONFIG_NET_NTCP_READAHEAD_BUFFERS Defined to be greater than zeroIn order to for select to work with incoming connections, you must also select:
CONFIG_NET_TCPBACKLOG
Incoming connections pend in a backlog until accept() is called.
The size of the backlog is selected when listen() is called.Input Parameters:
fds. List of structures describing file descriptors to be monitored.nfds. The number of entries in the list.timeout. Specifies an upper limit on the time for which poll() will
block in milliseconds. A negative value of timeout means an infinite
timeout.Returned Values:
On success, the number of structures that have nonzero errno is set appropriately:
EBADF. An invalid file descriptor was given in one of the sets.EFAULT. The fds address is invalidEINTR. A signal occurred before any requested event.EINVAL. The nfds value exceeds a system limit.ENOMEM. There was no space to allocate internal data structures.ENOSYS. One or more of the drivers supporting the file descriptor does not support the poll method.Function Prototype:
#include <sys/select.h>
int select(int nfds, FAR fd_set *readfds, FAR fd_set *writefds,
FAR fd_set *exceptfds, FAR struct timeval *timeout);
Description:
select() allows a program to monitor multiple file descriptors, waiting
until one or more of the file descriptors become "ready" for some class
of I/O operation (e.g., input possible). A file descriptor is
considered ready if it is possible to perform the corresponding I/O
operation (e.g., read(2)) without blocking.
NOTE: poll() is the fundamental API for performing such monitoring
operation under NuttX. select() is provided for compatibility and
is simply a layer of added logic on top of poll(). As such, select()
is more wasteful of resources and poll() is the recommended API to be
used.
Input Parameters:
nfds. the maximum file descriptor number (+1) of any descriptor in any of the three sets.readfds. the set of descriptions to monitor for read-ready eventswritefds. the set of descriptions to monitor for write-ready eventsexceptfds. the set of descriptions to monitor for error eventstimeout. Return at this time if none of these events of interest occur.Returned Values:
0: Timer expired>0: The number of bits set in the three sets of descriptors-1: An error occurred (errno will be set appropriately,
see poll()).#include <dirent.h> int closedir(DIR *dirp); FAR DIR *opendir(const char *path); FAR struct dirent *readdir(FAR DIR *dirp); int readdir_r(FAR DIR *dirp, FAR struct dirent *entry, FAR struct dirent **result); void rewinddir(FAR DIR *dirp); void seekdir(FAR DIR *dirp, int loc); int telldir(FAR DIR *dirp);
#include <unistd.h> int chdir(FAR const char *path); FAR char *getcwd(FAR char *buf, size_t size);
#include <stdio.h> int fclose(FILE *stream); int fflush(FILE *stream); int feof(FILE *stream); /* Prototyped but not implemented */ int ferror(FILE *stream); /* Prototyped but not implemented */ int fgetc(FILE *stream); int fgetpos(FILE *stream, fpos_t *pos); char *fgets(char *s, int n, FILE *stream); FILE *fopen(const char *path, const char *type); int fprintf(FILE *stream, const char *format, ...); int fputc(int c, FILE *stream); int fputs(const char *s, FILE *stream); size_t fread(void *ptr, size_t size, size_t n_items, FILE *stream); int fseek(FILE *stream, long int offset, int whence); int fsetpos(FILE *stream, fpos_t *pos); long ftell(FILE *stream); size_t fwrite(const void *ptr, size_t size, size_t n_items, FILE *stream); char *gets(char *s); int printf(const char *format, ...); int puts(const char *s); int rename(const char *source, const char *target); int sprintf(char *dest, const char *format, ...); int ungetc(int c, FILE *stream); int vprintf(const char *s, va_list ap); int vfprintf(FILE *stream, const char *s, va_list ap); int vsprintf(char *buf, const char *s, va_list ap); FILE *fdopen(int fd, const char *type); int fstat(int fd, FAR struct stat *buf); /* Prototyped but not implemented */ int mkdir(const char *path, mode_t mode); int rmdir(const char *path); int stat(const char *path, FAR struct stat *buf); int statfs(const char *path, FAR struct statfs *buf); /* Prototyped but not implemented */
pipeFunction Prototype:
#include <unistd.h> int pipe(int filedes[2]);
Description:
pipe() creates a pair of file descriptors, pointing to a pipe inode, and
places them in the array pointed to by filedes.
filedes[0] is for reading, filedes[1] is for writing.
Input Parameters:
filedes[2]. The user provided array in which to catch the pipe file descriptors.Returned Values:
0 is returned on success; otherwise, -1 is returned with errno set appropriately.
mkfifoFunction Prototype:
#include <sys/stat.h> int mkfifo(FAR const char *pathname, mode_t mode);
Description:
mkfifo() makes a FIFO device driver file with name pathname.
Unlike Linux, a NuttX FIFO is not a special file type but simply a device driver instance.
mode specifies the FIFO's permissions (but is ignored in the current implementation).
Once the FIFO has been created by mkfifo(), any thread can open it for
reading or writing, in the same way as an ordinary file.
However, it must have been opened from both reading and writing before input or output can be performed.
This FIFO implementation will block all attempts to open a FIFO read-only until at least one thread has opened the FIFO for writing.
If all threads that write to the FIFO have closed, subsequent calls to read() on the FIFO will return 0 (end-of-file).
Input Parameters:
pathname.
The full path to the FIFO instance to attach to or to create (if not already created).
mode.
Ignored for now
Returned Values:
0 is returned on success; otherwise, -1 is returned with errno set appropriately.
mkfatfsFunction Prototype:
#include <nuttx/mkfatfs.h> int mkfatfs(FAR const char *pathname, FAR struct fat_format_s *fmt);
Description:
The mkfats() formats a FAT file system image on the block
device specified by pathname
Assumptions: The caller must assure that the block driver is not mounted and not in use when this function is called. The result of formatting a mounted device is indeterminate (but likely not good).
Input Parameters:
pathname
The full path to the registered block driver in the file system.
fmt
A reference to an instance of a structure that provides caller-selectable
attributes of the created FAT file system.
struct fat_format_s
{
ubyte ff_nfats; /* Number of FATs */
ubyte ff_fattype; /* FAT size: 0 (autoselect), 12, 16, or 32 */
ubyte ff_clustshift; /* Log2 of sectors per cluster: 0-5, 0xff (autoselect) */
ubyte ff_volumelabel[11]; /* Volume label */
uint16 ff_backupboot; /* Sector number of the backup boot sector (0=use default)*/
uint16 ff_rootdirentries; /* Number of root directory entries */
uint16 ff_rsvdseccount; /* Reserved sectors */
uint32 ff_hidsec; /* Count of hidden sectors preceding fat */
uint32 ff_volumeid; /* FAT volume id */
uint32 ff_nsectors; /* Number of sectors from device to use: 0: Use all */
};
Returned Values:
Zero (OK) on success;
-1 (ERROR) on failure with errno set appropriately:
EINVAL -
NULL block driver string, bad number of FATS in fmt,
bad FAT size in fmt, bad cluster size in fmt
ENOENT -
pathname does not refer to anything in the filesystem.
ENOTBLK -
pathname does not refer to a block driver
EACCESS -
block driver does not support write or geometry methods
mmap() and eXecute In Place (XIP)
NuttX operates in a flat open address space.
Therefore, it generally does not require mmap() functionality.
There is one one exception:
mmap() is the API that is used to support direct access to random
access media under the following very restrictive conditions:
FIOC_MMAP ioctl command.
Any file system that maps files contiguously on the media should support this
ioctl command.
By comparison, most file system scatter files over the media in non-contiguous
sectors. As of this writing, ROMFS is the only file system that meets this requirement.
BIOC_XIPBASE ioctl command
that maps the underlying media to a randomly accessible address.
At present, only the RAM/ROM disk driver does this.
mmapFunction Prototype:
#include <sys/mman.h> int mkfatfs(FAR const char *pathname, FAR struct fat_format_s *fmt); FAR void *mmap(FAR void *start, size_t length, int prot, int flags, int fd, off_t offset)
Description:
mmap() as needed to support eXecute In Place (XIP)
operation (as described above).
Input Parameters:
start
A hint at where to map the memory -- ignored.
The address of the underlying media is fixed and cannot be re-mapped without MMU support.
length
The length of the mapping -- ignored.
The entire underlying media is always accessible.
prot
See the PROT_* definitions in sys/mman.h.
PROT_NONE - Will cause an error.
PROT_READ - PROT_WRITE and PROT_EXEC also assumed.
PROT_WRITE - PROT_READ and PROT_EXEC also assumed.
PROT_EXEC - PROT_READ and PROT_WRITE also assumed.
flags
See the MAP_* definitions in sys/mman.h.
MAP_SHARED - Required
MAP_PRIVATE - Will cause an error
MAP_FIXED - Will cause an error
MAP_FILE - Ignored
MAP_ANONYMOUS - Will cause an error
MAP_ANON - Will cause an error
MAP_GROWSDOWN - Ignored
MAP_DENYWRITE - Will cause an error
MAP_EXECUTABLE - Ignored
MAP_LOCKED - Ignored
MAP_NORESERVE - Ignored
MAP_POPULATE - Ignored
AP_NONBLOCK - Ignored
fd
file descriptor of the backing file -- required.
offset
The offset into the file to map.
Returned Values:
On success, mmap() returns a pointer to the mapped area.
On error, the value MAP_FAILED is returned, and errno is set appropriately.
ENOSYS -
Returned if any of the unsupported mmap() features are attempted.
EBADF -
fd is not a valid file descriptor.
EINVAL -
Length is 0. flags contained neither MAP_PRIVATE or MAP_SHARED, or
contained both of these values.
ENODEV -
The underlying filesystem of the specified file does not support memory mapping.
2.12 Network Interfaces |
NuttX includes a simple interface layer based on uIP (see http://www.sics.se). NuttX supports subset of a standard socket interface to uIP. These network feature can be enabled by settings in the architecture configuration file. Those socket APIs are discussed in the following paragraphs.
socketFunction Prototype:
#include <sys/socket.h> int socket(int domain, int type, int protocol);
Description: socket() creates an endpoint for communication and returns a descriptor.
Input Parameters:
domain: (see sys/socket.h)type: (see sys/socket.h)protocol: (see sys/socket.h)
Returned Values:
0 on success; -1 on error with errno set appropriately:
EACCES.
Permission to create a socket of the specified type and/or protocol is denied.EAFNOSUPPORT.
The implementation does not support the specified address family.EINVAL.
Unknown protocol, or protocol family not available.EMFILE.
Process file table overflow.ENFILE
The system limit on the total number of open files has been reached.ENOBUFS or ENOMEM.
Insufficient memory is available. The socket cannot be created until sufficient resources are freed.EPROTONOSUPPORT.
The protocol type or the specified protocol is not supported within this domain.bindFunction Prototype:
#include <sys/socket.h> int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
Description:
bind() gives the socket sockfd the local address addr.
addr is addrlen bytes long. Traditionally, this is called
"assigning a name to a socket." When a socket is created with socket(),
it exists in a name space (address family) but has no name assigned.
Input Parameters:
sockfd: Socket descriptor from socket.addr: Socket local address.addrlen: Length of addr.
Returned Values:
0 on success; -1 on error with errno set appropriately:
EACCES
The address is protected, and the user is not the superuser.EADDRINUSE
The given address is already in use.EBADF
sockfd is not a valid descriptor.EINVAL
The socket is already bound to an address.ENOTSOCK
sockfd is a descriptor for a file, not a socket.connectFunction Prototype:
#include <sys/socket.h> int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
Description:
connect() connects the socket referred to by the file descriptor
sockfd to the address specified by addr.
The addrlen argument specifies the size of addr.
The format of the address in addr is determined by the address space
of the socket sockfd.
If the socket sockfd is of type SOCK_DGRAM then addr is the address
to which datagrams are sent by default, and the only address from which
datagrams are received. If the socket is of type SOCK_STREAM or
SOCK_SEQPACKET, this call attempts to make a connection to the socket
that is bound to the address specified by addr.
Generally, connection-based protocol sockets may successfully connect()
only once; connectionless protocol sockets may use connect() multiple
times to change their association. Connectionless sockets may dissolve
the association by connecting to an address with the sa_family member of
sockaddr set to AF_UNSPEC.
Input Parameters:
sockfd: Socket descriptor returned by socket()addr: Server address (form depends on type of socket)addrlen: Length of actual addr
Returned Values:
0 on success; -1 on error with errno set appropriately:
EACCES or EPERM:
The user tried to connect to a broadcast address without having the
socket broadcast flag enabled or the connection request failed
because of a local firewall rule.EADDRINUSE
Local address is already in use.EAFNOSUPPORT
The passed address didn't have the correct address family in its
sa_family field.EAGAIN
No more free local ports or insufficient entries in the routing
cache. For PF_INET.EALREADY
The socket is non-blocking and a previous connection attempt has
not yet been completed.EBADF
The file descriptor is not a valid index in the descriptor table.ECONNREFUSED
No one listening on the remote address.EFAULT
The socket structure address is outside the user's address space.EINPROGRESS
The socket is non-blocking and the connection cannot be completed
immediately.EINTR
The system call was interrupted by a signal that was caught.EISCONN
The socket is already connected.ENETUNREACH
Network is unreachable.ENOTSOCK
The file descriptor is not associated with a socket.ETIMEDOUT
Timeout while attempting connection. The server may be too busy
to accept new connections.Function Prototype:
#include <sys/socket.h> int listen(int sockfd, int backlog);
Description:
To accept connections, a socket is first created with socket(), a
willingness to accept incoming connections and a queue limit for incoming
connections are specified with listen(), and then the connections are
accepted with accept(). The listen() call applies only to sockets of
type SOCK_STREAM or SOCK_SEQPACKET.
Input Parameters:
sockfd: Socket descriptor of the bound socket.backlog: The maximum length the queue of pending connections may grow.
If a connection request arrives with the queue full, the client may receive an error
with an indication of ECONNREFUSED or, if the underlying protocol supports retransmission,
the request may be ignored so that retries succeed.
Returned Values:
On success, zero is returned. On error, -1 is returned, and
errno is set appropriately.
EADDRINUSE: Another socket is already listening on the same port.EBADF: The argument sockfd is not a valid descriptor.ENOTSOCK: The argument sockfd is not a socket.EOPNOTSUPP: The socket is not of a type that supports the listen operation.Function Prototype:
#include <sys/socket.h> int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
Description:
The accept() function is used with connection-based socket types
(SOCK_STREAM, SOCK_SEQPACKET and SOCK_RDM).
It extracts the first connection request on the queue of pending connections,
creates a new connected socket with most of the same properties as sockfd,
and allocates a new socket descriptor for the socket, which is returned. The
newly created socket is no longer in the listening state. The original
socket sockfd is unaffected by this call. Per file descriptor flags
are not inherited across an accept.
The sockfd argument is a socket descriptor that has been created with
socket(), bound to a local address with bind(), and is listening for
connections after a call to listen().
On return, the addr structure is filled in with the address of the
connecting entity. The addrlen argument initially contains the size
of the structure pointed to by addr; on return it will contain the
actual length of the address returned.
If no pending connections are present on the queue, and the socket is
not marked as non-blocking, accept blocks the caller until a connection
is present. If the socket is marked non-blocking and no pending
connections are present on the queue, accept returns EAGAIN.
Input Parameters:
sockfd: Socket descriptor of the listening socket.addr: Receives the address of the connecting client.addrlen: Input: allocated size of addr, Return: returned size of addr.Returned Values: Returns -1 on error. If it succeeds, it returns a non-negative integer that is a descriptor for the accepted socket.
EAGAIN or EWOULDBLOCK:
The socket is marked non-blocking and no connections are present to be accepted.EBADF:
The descriptor is invalid.ENOTSOCK:
The descriptor references a file, not a socket.EOPNOTSUPP:
The referenced socket is not of type SOCK_STREAM.EINTR:
The system call was interrupted by a signal that was caught before a valid connection arrived.ECONNABORTED:
A connection has been aborted.EINVAL:
Socket is not listening for connections.EMFILE:
The per-process limit of open file descriptors has been reached.ENFILE:
The system maximum for file descriptors has been reached.EFAULT:
The addr parameter is not in a writable part of the user address space.ENOBUFS or ENOMEM:
Not enough free memory.EPROTO:
Protocol error.EPERM:
Firewall rules forbid connection.sendFunction Prototype:
#include <sys/socket.h> ssize_t send(int sockfd, const void *buf, size_t len, int flags);
Description:
The send() call may be used only when the socket is in a connected state
(so that the intended recipient is known).
The only difference between send() and write() is the
presence of flags.
With zero flags parameter, send() is equivalent to
write(). Also, send(s,buf,len,flags) is
equivalent to sendto(s,buf,len,flags,NULL,0).
Input Parameters:
sockfd: Socket descriptor of socket
buf: Data to send
len: Length of data to send
flags: Send flags
Returned Values:
See sendto().
sendtoFunction Prototype:
#include <sys/socket.h>
ssize_t sendto(int sockfd, const void *buf, size_t len, int flags,
const struct sockaddr *to, socklen_t tolen);
Description:
If sendto() is used on a connection-mode (SOCK_STREAM, SOCK_SEQPACKET)
socket, the parameters to and tolen are ignored (and the error EISCONN
may be returned when they are not NULL and 0), and the error ENOTCONN is
returned when the socket was not actually connected.
Input Parameters:
sockfd: Socket descriptor of socket
buf: Data to send
len: Length of data to send
flags: Send flags
to: Address of recipient
tolen: The length of the address structure
Returned Values:
On success, returns the number of characters sent. On error, -1 is returned,
and errno is set appropriately:
EAGAIN or EWOULDBLOCK.
The socket is marked non-blocking and the requested operation would block.
EBADF.
An invalid descriptor was specified.
ECONNRESET.
Connection reset by peer.
EDESTADDRREQ.
The socket is not connection-mode, and no peer address is set.
EFAULT.
An invalid user space address was specified for a parameter.
EINTR.
A signal occurred before any data was transmitted.
EINVAL.
Invalid argument passed.
EISCONN.
The connection-mode socket was connected already but a recipient
was specified. (Now either this error is returned, or the recipient
specification is ignored.)
EMSGSIZE.
The socket type requires that message be sent atomically, and the
size of the message to be sent made this impossible.
ENOBUFS.
The output queue for a network interface was full. This generally
indicates that the interface has stopped sending, but may be
caused by transient congestion.
ENOMEM.
No memory available.
ENOTCONN.
The socket is not connected, and no target has been given.
ENOTSOCK.
The argument s is not a socket.
EOPNOTSUPP.
Some bit in the flags argument is inappropriate for the socket type.
EPIPE.
The local end has been shut down on a connection oriented socket.
In this case the process will also receive a SIGPIPE unless
MSG_NOSIGNAL is set.
recvFunction Prototype:
#include <sys/socket.h> ssize_t recv(int sockfd, void *buf, size_t len, int flags);
Description:
The recv() call is identical to
recvfrom() with a NULL
from parameter.
Input Parameters:
Returned Values:
see recvfrom().
Zero on success.
recvfromFunction Prototype:
#include <sys/socket.h>
ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags,
struct sockaddr *from, socklen_t *fromlen);
Description:
recvfrom() receives messages from a socket, and may be used to receive
data on a socket whether or not it is connection-oriented.
If from is not NULL, and the underlying protocol provides the source
address, this source address is filled in. The argument fromlen
initialized to the size of the buffer associated with from, and modified
on return to indicate the actual size of the address stored there.
Input Parameters:
sockfd: Socket descriptor of socket.buf: Buffer to receive data.len: Length of buffer.flags: Receive flags.from: Address of source.fromlen: The length of the address structure.
Returned Values:
On success, returns the number of characters sent.
On error, -1 is returned, and errno is set appropriately:
EAGAIN.
The socket is marked non-blocking and the receive operation would block,
or a receive timeout had been set and the timeout expired before data
was received.
EBADF.
The argument sockfd is an invalid descriptor.
ECONNREFUSED.
A remote host refused to allow the network connection (typically because
it is not running the requested service).
EFAULT.
The receive buffer pointer(s) point outside the process's address space.
EINTR.
The receive was interrupted by delivery of a signal before any data were
available.
EINVAL.
Invalid argument passed.
ENOMEM.
Could not allocate memory.
ENOTCONN.
The socket is associated with a connection-oriented protocol and has
not been connected.
ENOTSOCK.
The argument sockfd does not refer to a socket.
setsockoptFunction Prototype:
#include <sys/socket.h>
int setsockopt(int sockfd, int level, int option,
const void *value, socklen_t value_len);
Description:
setsockopt() sets the option specified by the option argument,
at the protocol level specified by the level argument, to the value
pointed to by the value argument for the socket associated with the
file descriptor specified by the sockfd argument.
The level argument specifies the protocol level of the option. To set
options at the socket level, specify the level argument as SOL_SOCKET.
See sys/socket.h for a complete list of values for the option argument.
Input Parameters:
sockfd: Socket descriptor of socket
level: Protocol level to set the option
option: identifies the option to set
value: Points to the argument value
value_len: The length of the argument value
Returned Values:
On success, returns the number of characters sent.
On error, -1 is returned, and errno is set appropriately:
BADF.
The sockfd argument is not a valid socket descriptor.
DOM.
The send and receive timeout values are too big to fit into the
timeout fields in the socket structure.
INVAL.
The specified option is invalid at the specified socket level or the
socket has been shut down.
ISCONN.
The socket is already connected, and a specified option cannot be set
while the socket is connected.
NOPROTOOPT.
The option is not supported by the protocol.
NOTSOCK.
The sockfd argument does not refer to a socket.
NOMEM.
There was insufficient memory available for the operation to complete.
NOBUFS.
Insufficient resources are available in the system to complete the call.
getsockoptFunction Prototype:
#include <sys/socket.h>
int getsockopt(int sockfd, int level, int option,
void *value, socklen_t *value_len);
Description:
getsockopt() retrieve thse value for the option specified by the
option argument for the socket specified by the sockfd argument. If
the size of the option value is greater than value_len, the value
stored in the object pointed to by the value argument will be silently
truncated. Otherwise, the length pointed to by the value_len argument
will be modified to indicate the actual length of thevalue.
The level argument specifies the protocol level of the option. To
retrieve options at the socket level, specify the level argument as
SOL_SOCKET.
See sys/socket.hfor a complete list of values for the option argument.
Input Parameters:
sockfd Socket descriptor of socket
level Protocol level to set the option
option identifies the option to get
value Points to the argument value
value_len The length of the argument value
Returned Values:
On success, returns the number of characters sent.
On error, -1 is returned, and errno is set appropriately:
BADF.
The sockfd argument is not a valid socket descriptor.INVAL.
The specified option is invalid at the specified socket level or the
socket has been shutdown.NOPROTOOPT.
The option is not supported by the protocol.NOTSOCK.
The sockfd argument does not refer to a socket.NOBUFS
Insufficient resources are available in the system to complete the call.
3.0 OS Data Structures |
3.1 Scalar Types |
Many of the types used to communicate with NuttX are simple scalar types. These types are used to provide architecture independence of the OS from the application. The scalar types used at the NuttX interface include:
3.2 Hidden Interface Structures |
Several of the types used to interface with NuttX are structures that are intended to be hidden from the application. From the standpoint of the application, these structures (and structure pointers) should be treated as simple handles to reference OS resources. These hidden structures include:
In order to maintain portability, applications should not reference specific elements within these hidden structures. These hidden structures will not be described further in this user's manual.
3.3 Access to the
|
A pointer to the thread-specific errno value is available through a
function call:
Function Prototype:
#include <errno.h>
#define errno *get_errno_ptr()
int *get_errno_ptr( void )
Description:
get_errno_ptr() returns a pointer to the thread-specific errno value.
Note that the symbol errno is defined to be get_errno_ptr() so that the usual
access by referencing the symbol errno will work as expected.
There is a unique, private errno value for each NuttX task.
However, the implementation of errno differs somewhat from the use of
errno in most multi-threaded process environments:
In NuttX, each pthread will also have its own private copy of errno and the
errno will not be shared between pthreads.
This is, perhaps, non-standard but promotes better thread independence.
Input Parameters: None
Returned Values:
errno value.
3.4 User Interface Structures |
main_t defines the type of a task entry point. main_t is declared in sys/types.h as:
typedef int (*main_t)(int argc, char *argv[]);
This structure is used to pass scheduling priorities to and from NuttX;
struct sched_param
{
int sched_priority;
};
This structure is used to pass timing information between the NuttX and a user application:
struct timespec
{
time_t tv_sec; /* Seconds */
long tv_nsec; /* Nanoseconds */
};
This structure is used to communicate message queue attributes between NuttX and a MoBY application:
struct mq_attr {
size_t mq_maxmsg; /* Max number of messages in queue */
size_t mq_msgsize; /* Max message size */
unsigned mq_flags; /* Queue flags */
size_t mq_curmsgs; /* Number of messages currently in queue */
};
The following structure defines the action to take for given signal:
struct sigaction
{
union
{
void (*_sa_handler)(int);
void (*_sa_sigaction)(int, siginfo_t *, void *);
} sa_u;
sigset_t sa_mask;
int sa_flags;
};
#define sa_handler sa_u._sa_handler
#define sa_sigaction sa_u._sa_sigaction
The following types is used to pass parameters to/from signal handlers:
typedef struct siginfo
{
int si_signo;
int si_code;
union sigval si_value;
} siginfo_t;
This defines the type of the struct siginfo si_value field and is used to pass parameters with signals.
union sigval
{
int sival_int;
void *sival_ptr;
};
The following is used to attach a signal to a message queue to notify a task when a message is available on a queue.
struct sigevent
{
int sigev_signo;
union sigval sigev_value;
int sigev_notify;
};
When a watchdog expires, the callback function with this type is called:
typedef void (*wdentry_t)(int argc, ...);
Where argc is the number of uint32 type arguments that follow.
The arguments are passed as uint32 values. For systems where the sizeof(pointer) < sizeof(uint32), the following union defines the alignment of the pointer within the uint32. For example, the SDCC MCS51 general pointer is 24-bits, but uint32 is 32-bits (of course).
union wdparm_u
{
void *pvarg;
uint32 *dwarg;
};
typedef union wdparm_u wdparm_t;
For most 32-bit systems, pointers and uint32 are the same size For systems where sizeof(pointer) > sizeof(uint32), we will have to do some redesign.
Index |