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nuttx/TODO
Gregory Nutt 5f9ee79298 I/O Expander: Remove hard-coded PCA9555 fields from ioexpander.h definitons. Add support for an attach() method that may be used when any subset of pin interrupts occur. 
PCA9555 Driver:  Replace the signalling logic with a simple callback using the new definitons of ioexpander.h.  This repartitioning of functionality is necessary because (1) the I/O expander driver is the lower-lower part of any driver that uses GPIOs (include the GPIO driver itself) and should not be interacting directly with the much higher level application layer.  And (2) in order to be compatible with the GPIO driver (and any arbitrary upper half driver), the PCA9555 should not directly signal, but should call back into the upper half.  The upper half driver that interacts directly with the application is the appropriate place to be generating signal.
2016-07-31 11:09:47 -06:00

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NuttX TODO List (Last updated July 20, 2016)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This file summarizes known NuttX bugs, limitations, inconsistencies with
standards, things that could be improved, and ideas for enhancements. This
TODO list does not include issues associated with individual boar ports. See
also the individual README.txt files in the configs/ sub-directories for
issues related to each board port.
nuttx/:
(13) Task/Scheduler (sched/)
(1) Memory Management (mm/)
(3) Signals (sched/signal, arch/)
(2) pthreads (sched/pthread)
(0) Message Queues (sched/mqueue)
(9) Kernel/Protected Build
(3) C++ Support
(6) Binary loaders (binfmt/)
(11) Network (net/, drivers/net)
(4) USB (drivers/usbdev, drivers/usbhost)
(0) Other drivers (drivers/)
(11) Libraries (libc/, libm/)
(11) File system/Generic drivers (fs/, drivers/)
(8) Graphics subsystem (graphics/)
(2) Build system / Toolchains
(3) Linux/Cywgin simulation (arch/sim)
(4) ARM (arch/arm/)
apps/ and other Add-Ons:
(3) Network Utilities (apps/netutils/)
(2) NuttShell (NSH) (apps/nshlib)
(1) System libraries apps/system (apps/system)
(1) Pascal add-on (pcode/)
(4) Other Applications & Tests (apps/examples/)
o Task/Scheduler (sched/)
^^^^^^^^^^^^^^^^^^^^^^^
Title: CHILD PTHREAD TERMINATION
Description: When a tasks exits, shouldn't all of its child pthreads also be
terminated?
Status: Closed. No, this behavior will not be implemented.
Priority: Medium, required for good emulation of process/pthread model.
Title: pause() NON-COMPLIANCE
Description: In the POSIX description of this function is the pause() function
will suspend the calling thread until delivery of a signal whose
action is either to execute a signal-catching function or to
terminate the process. The current implementation only waits for
any non-blocked signal to be received. It should only wake up if
the signal is delivered to a handler.
Status: Open.
Priority: Medium Low.
Title: ON-DEMAND PAGING INCOMPLETE
Description: On-demand paging has recently been incorporated into the RTOS.
The design of this feature is described here:
http://www.nuttx.org/NuttXDemandPaging.html.
As of this writing, the basic feature implementation is
complete and much of the logic has been verified. The test
harness for the feature exists only for the NXP LPC3131 (see
configs/ea3131/pgnsh and locked directories). There are
some limitations of this testing so I still cannot say that
the feature is fully functional.
Status: Open. This has been put on the shelf for some time.
Priority: Medium-Low
Title: GET_ENVIRON_PTR()
Description: get_environ_ptr() (sched/sched_getenvironptr.c) is not implemented.
The representation of the environment strings selected for
NuttX is not compatible with the operation. Some significant
re-design would be required to implement this function and that
effort is thought to be not worth the result.
Status: Open. No change is planned.
Priority: Low -- There is no plan to implement this.
Title: TIMER_GETOVERRUN()
Description: timer_getoverrun() (sched/timer_getoverrun.c) is not implemented.
Status: Open
Priority: Low -- There is no plan to implement this.
Title: INCOMPATIBILITIES WITH execv() AND execl()
Description: Simplified 'execl()' and 'execv()' functions are provided by
NuttX. NuttX does not support processes and hence the concept
of overlaying a tasks process image with a new process image
does not make any sense. In NuttX, these functions are
wrapper functions that:
1. Call the non-standard binfmt function 'exec', and then
2. exit(0).
As a result, the current implementations of 'execl()' and
'execv()' suffer from some incompatibilities, the most
serious of these is that the exec'ed task will not have
the same task ID as the vfork'ed function. So the parent
function cannot know the ID of the exec'ed task.
Status: Open
Priority: Medium Low for now
Title: ISSUES WITH atexit() AND on_exit()
Description: These functions execute with the following bad properties:
1. They run with interrupts disabled,
2. They run in supervisor mode (if applicable), and
3. They do not obey any setup of PIC or address
environments. Do they need to?
The fix for all of these issues it to have the callbacks
run on the caller's thread (as with signal handlers).
Status: Open
Priority: Medium Low. This is an important change to some less
important interfaces. For the average user, these
functions are just fine the way they are.
Title: execv() AND vfork()
Description: There is a problem when vfork() calls execv() (or execl()) to
start a new application: When the parent thread calls vfork()
it receives and gets the pid of the vforked task, and *not*
the pid of the desired execv'ed application.
The same tasking arrangement is used by the standard function
posix_spawn(). However, posix_spawn uses the non-standard, internal
NuttX interface task_reparent() to replace the child's parent task
with the caller of posix_spawn(). That cannot be done with vfork()
because we don't know what vfork() is going to do.
Any solution to this is either very difficult or impossible without
an MMU.
Status: Open
Priority: Low (it might as well be low since it isn't going to be fixed).
Title: errno IS NOT SHARED AMONG THREADS
Description: In NuttX, the errno value is unique for each thread. But for
bug-for-bug compatibility, the same errno should be shared by
the task and each thread that it creates. It is *very* easy
to make this change: Just move the pterrno field from
struct tcb_s to struct task_group_s. However, I am still not
sure if this should be done or not.
Status: Closed. The existing solution is better (although its
incompatibilities could show up in porting some code).
Priority: Low
Title: REMOVE TASK_DELETE
Description: Need to remove or fix task delete. This interface is non-
standard and not safe. Arbitrary deleting tasks can cause
serious problems such as memory leaks. Better to remove it
than to retain it as a latent bug.
Currently used within the OS and also part of the
implementation of pthread_cancel() and task_restart() (which
should also go for the same reasons). It is used in
NxWM::CNxConsole to terminate console tasks and also in
apps/netutils/thttpd to kill CGI tasks that timeout.
Status: Open
Priority: Low and not easily removable.
Title: RELEASE SEMAPHORES HELD BY CANCELED THREADS:
Description: Commit: fecb9040d0e54baf14b729e556a832febfe8229e: "In
case a thread is doing a blocking operation (e.g. read())
on a serial device, while it is being terminated by
pthread_cancel(), then uart_close() gets called, but
the semaphore (dev->recv.sem in the above example) is
still blocked.
"This means that once the serial device is opened next
time, data will arrive on the serial port (and driver
interrupts handled as normal), but the received characters
never arrive in the reader thread.
This patch addresses the problem by re-initializing the
semaphores on the last uart_close() on the device."
Yahoo! Groups message 7726: "I think that the system
should be required to handle pthread_cancel safely in
all cases. In the NuttX model, a task is like a Unix
process and a pthread is like a Unix thread. Canceling
threads should always be safe (or at least as unsafe) as
under Unix because the model is complete for pthreads...
"So, in my opinion, this is a generic system issue, not
specific to the serial driver. I could also implement
logic to release all semaphores held by a thread when
it exits -- but only if priority inheritance is enabled;
because only in that case does the code have any memory
of which threads actually hold the semaphore.
"The patch I just incorporated is also insufficient. It
works only if the serial driver is shut down when the
thread is canceled. But what if there are other open
references to the driver? Then the driver will not be
shut down, the semaphores will not be re-initialized, and
the semaphore counts will still be off by one.
"I think that the system needs to automatically release any
semaphores held by a thread being killed asynchronously?
It seems necessary to me."
UPDATE; The logic enabled when priority inheritance is
enabled for this purpose is insufficient. It provides
hooks so that given a semaphore it can traverse all
holders. What is needed would be logic so that given
a task, you can traverse all semaphores held by the task,
releasing each semaphore count held by the exiting task.
Nothing like this exists now so that solution is not
imminent.
UPDATE: The basic fix to release the semaphore count if
a thread is killed via pthread_cancel() or task_delete()
has been implemented (2014-12-13). See the new file:
sched/semaphore/sem_recover.c However, the general
issue of freeing semaphores when a thread exists still
exists.
Status: Open
Priority: Medium-ish
Title: SCALABILITY
Description: Task control information is retained in simple lists. This
is completely appropriate for small embedded systems where
the number of tasks, N, is relatively small. Most list
operations are O(N). This could become as issue if N gets
very large.
In that case, these simple lists should be replaced with
something more performant such as a balanced tree in the
case of ordered lists. Fortunately, most internal lists are
hidden behind simple accessor functions and so the internal
data structures can be changed if need with very little impact.
Explicitly reference to the list structure are hidden behind
the macro this_task().
Status: Open
Priority: Low. Things are just the way that we want them for the way
that NuttX is used today.
o Memory Management (mm/)
^^^^^^^^^^^^^^^^^^^^^^^
Title: FREE MEMORY ON TASK EXIT
Description: Add an option to free all memory allocated by a task when the
task exits. This is probably not be worth the overhead for a
deeply embedded system.
There would be complexities with this implementation as well
because often one task allocates memory and then passes the
memory to another: The task that "owns" the memory may not
be the same as the task that allocated the memory.
Update. From the NuttX forum:
...there is a good reason why task A should never delete task B.
That is because you will strand memory resources. Another feature
lacking in most flat address space RTOSs is automatic memory
clean-up when a task exits.
That behavior just comes for free in a process-based OS like Linux:
Each process has its own heap and when you tear down the process
environment, you naturally destroy the heap too.
But RTOSs have only a single, shared heap. I have spent some time
thinking about how you could clean up memory required by a task
when a task exits. It is not so simple. It is not as simple as
just keeping memory allocated by a thread in a list then freeing
the list of allocations when the task exists.
It is not that simple because you don't know how the memory is
being used. For example, if task A allocates memory that is used
by task B, then when task A exits, you would not want to free that
memory needed by task B. In a process-based system, you would
have to explicitly map shared memory (with reference counting) in
order to share memory. So the life of shared memory in that
environment is easily managed.
I have thought that the way that this could be solved in NuttX
would be: (1) add links and reference counts to all memory allocated
by a thread. This would increase the memory allocation overhead!
(2) Keep the list head in the TCB, and (3) extend mmap() and munmap()
to include the shared memory operations (which would only manage
the reference counting and the life of the allocation).
Then what about pthreads? Memory should not be freed until the last
pthread in the group exists. That could be done with an additional
reference count on the whole allocated memory list (just as streams
and file descriptors are now shared and persist until the last
pthread exits).
I think that would work but to me is very unattractive and
inconsistent with the NuttX "small footprint" objective. ...
Other issues:
- Memory free time would go up because you would have to remove
the memory from that list in free().
- There are special cases inside the RTOS itself. For example,
if task A creates task B, then initial memory allocations for
task B are created by task A. Some special allocators would
be required to keep this memory on the correct list (or on
no list at all).
Updated 2016-06-25:
For processors with an MMU (Memory Management Unit), NuttX can be
built in a kernel mode. In that case, each process will have a
local copy of its heap (filled with sbrk()) and when the process
exits, its local heap will be destroyed and the underlying page
memory is recovered.
So in this case, NuttX work just link Linux or or *nix systems:
All memory allocated by processes or threads in processes will
be recovered when the process exists.
But not for the flat memory build. In that case, the issues
above do apply. There is no safe way to recover the memory in
that case (and even if there were, the additional overhead would
not be acceptable on most platforms).
This does not prohibit anyone from creating a wrapper for malloc()
and an atexit() callback that frees memory on task exit. People
are free and, in fact, encouraged, to do that. However, since
it is inherently unsafe, I would never incorporate anything
like that into NuttX.
Status: Open. No changes are planned.
Priority: Medium/Low, a good feature to prevent memory leaks but would
have negative impact on memory usage and code size.
o Signals (sched/signal, arch/)
^^^^^^^^^^^^^^^^^^^^^^^
Title: STANDARD SIGNALS
Description: 'Standard' signals and signal actions are not supported.
(e.g., SIGINT, SIGSEGV, etc).
Update: SIGCHLD is supported if so configured.
Status: Open. No further changes are planned.
Priority: Low, required by standards but not so critical for an
embedded system.
Title: SIGEV_THREAD
Description: Implementation of support for support for SIGEV_THREAD is available
only in the FLAT build mode because it uses the OS work queues to
perform the callback. The alternative for the PROTECTED and KERNEL
builds would be to create pthreads in the user space to perform the
callbacks. That is not a very attractive solution due to performance
issues. It would also require some additional logic to specify the
TCB of the parent so that the pthread could be bound to the correct
group.
There is also some user-space logic in libc/aio/lio_listio.c. That
logic could use the user-space work queue for the callbacks.
Status: Low, there are alternative designs. However, these features
are required by the POSIX standard.
Priority: Low for now
Title: SIGNAL NUMBERING
Description: In signal.h, the range of valid signals is listed as 0-31. However,
in many interfaces, 0 is not a valid signal number. The valid
signal number should be 1-32. The signal set operations would need
to map bits appropriately.
Status: Open
Priority: Low. Even if there are only 31 usable signals, that is still a lot.
o pthreads (sched/pthreads)
^^^^^^^^^^^^^^^^^
Title: CANCELLATION POINTS
Description: pthread_cancel(): Should implement cancellation points and
pthread_testcancel()
Status: Open. No changes are planned.
Priority: Low, probably not that useful
Title: PTHREAD_PRIO_PROTECT
Description: Extended pthread_mutexattr_setprotocol() support PTHREAD_PRIO_PROTECT:
"When a thread owns one or more mutexes initialized with the
PTHREAD_PRIO_PROTECT protocol, it shall execute at the higher of its
priority or the highest of the priority ceilings of all the mutexes
owned by this thread and initialized with this attribute, regardless of
whether other threads are blocked on any of these mutexes or not.
"While a thread is holding a mutex which has been initialized with
the PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT protocol attributes,
it shall not be subject to being moved to the tail of the scheduling queue
at its priority in the event that its original priority is changed,
such as by a call to sched_setparam(). Likewise, when a thread unlocks
a mutex that has been initialized with the PTHREAD_PRIO_INHERIT or
PTHREAD_PRIO_PROTECT protocol attributes, it shall not be subject to
being moved to the tail of the scheduling queue at its priority in the
event that its original priority is changed."
Status: Open. No changes planned.
Priority: Low -- about zero, probably not that useful. Priority inheritance is
already supported and is a much better solution. And it turns out
that priority protection is just about as complex as priority inheritance.
Excerpted from my post in a Linked-In discussion:
"I started to implement this HLS/"PCP" semaphore in an RTOS that I
work with (http://www.nuttx.org) and I discovered after doing the
analysis and basic code framework that a complete solution for the
case of a counting semaphore is still quite complex -- essentially
as complex as is priority inheritance.
"For example, suppose that a thread takes 3 different HLS semaphores
A, B, and C. Suppose that they are prioritized in that order with
A the lowest and C the highest. Suppose the thread takes 5 counts
from A, 3 counts from B, and 2 counts from C. What priority should
it run at? It would have to run at the priority of the highest
priority semaphore C. This means that the RTOS must maintain
internal information of the priority of every semaphore held by
the thread.
"Now suppose it releases one count on semaphore B. How does the
RTOS know that it still holds 2 counts on B? With some complex
internal data structure. The RTOS would have to maintain internal
information about how many counts from each semaphore are held
by each thread.
"How does the RTOS know that it should not decrement the priority
from the priority of C? Again, only with internal complexity. It
would have to know the priority of every semaphore held by
every thread.
"Providing the HLS capability on a simple pthread mutex would not
be such quite such a complex job if you allow only one mutex per
thread. However, the more general case seems almost as complex
as priority inheritance. I decided that the implementation does
not have value to me. I only wanted it for its reduced
complexity; in all other ways I believe that it is the inferior
solution. So I discarded a few hours of programming. Not a
big loss from the experience I gained."
o Message Queues (sched/mqueue)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
o Kernel/Protected Build
^^^^^^^^^^^^^^^^^^^^^^
Title: NSH PARTITIONING.
Description: There are issues with several NSH commands in the NuttX kernel
and protected build modes (where NuttX is built as a monolithic
kernel and user code must trap into the protected kernel via
syscalls). The current NSH implementation has several commands
that call directly into kernel internal functions for which
there is no syscall available. The commands cause link failures
in the kernel/protected build mode and must currently be disabled.
Here are known problems that must be fixed:
COMMAND KERNEL INTERFACE(s)
-------- ----------------------------------------------
mkfatfs mkfatfs
mkrd ramdisk_register()
ping icmp_ping()
mount foreach_mountpoint()
The busybox mkfatfs does not involve any OS calls; it does
its job by simply opening the block driver (using open/xopen)
and modifying it with write operations. See:
http://git.busybox.net/busybox/tree/util-linux/mkfs_vfat.c
Status: Open
Priority: Medium/High -- the kernel build configuration is not fully fielded
yet.
Title: apps/system PARTITIONING
Description: Several of the USB device helper applications in apps/system
violate OS/application partitioning and will fail on a kernel
or protected build. Many of these have been fixed by adding
the BOARDIOC_USBDEV_CONTROL boardctl() command. But there are
still issues.
These functions still call directly into operating system
functions:
- cdcacm_classobject - Called from apps/system/composite.
- usbmsc_configure - Called from apps/system/usbmsc and
apps/system/composite
- usbmsc_bindlun - Called from apps/system/usbmsc and
apps/system/composite
- usbmsc_exportluns - Called from apps/system/usbmsc.
Status: Open
Priority: Medium/High -- the kernel build configuration is not fully fielded
yet.
Title: NxTERM PARTITIONING.
Description: NxTerm is implemented (correctly) as a driver that resides
in the nuttx/ directory. However, the user interfaces must be
moved into a NuttX library or into apps/. Currently
applications calls to the NxTerm user interfaces are
undefined.
Status: Open
Priority: Medium
Title: C++ CONSTRUCTORS HAVE TOO MANY PRIVILEGES (PROTECTED MODE)
Description: When a C++ ELF module is loaded, its C++ constructors are called
via sched/task_starthook.c logic. This logic runs in protected mode.
The is a security hole because the user code runs with kernel-
privileges when the constructor executes.
Destructors likely have the opposite problem. The probably try to
execute some kernel logic in user mode? Obviously this needs to
be investigated further.
Status: Open
Priority: Low (unless you need build a secure C++ system).
Title: TOO MANY SYSCALLS
Description: There are a few syscalls that operate very often in user space.
Since syscalls are (relatively) time consuming this could be
a performance issue. Here is some numbers that I collected
in an application that was doing mostly printf output:
sem_post - 18% of syscalls
sem_wait - 18% of syscalls
getpid - 59% of syscalls
--------------------------
95% of syscalls
Obviously system performance could be improved greatly by simply
optimizing these functions so that they do not need to system calls
so frequently. getpid() is (I believe) part of the re-entrant
semaphore logic. Something like TLS might be used to retain the
thread's ID locally.
Linux, for example, has functions call up() and down(). up()
increments the semaphore count but does not call into the kernel
unless incrementing the count unblocks a task; similarly, down
decrements the count and does not call into the kernel unless
the count becomes negative the caller must be blocked.
Update:
"I am thinking that there should be a "magic" global, user-accessible
variable that holds the PID of the currently executing thread;
basically the PID of the task at the head of the ready-to-run list.
This variable would have to be reset each time the head of the ready-
to-run list changes.
"Then getpid() could be implemented in user space with no system call
by simply reading this variable.
"This one would be easy: Just a change to include/nuttx/userspace.h,
configs/*/kernel/up_userspace.c, libc/, sched/sched_addreadytorun.c, and
sched/sched_removereadytorun.c. That would eliminate 59% of the syscalls."
Update:
This is probably also just a symptom of the OS test that does mostly
console output. The requests for the pid() are part of the
implementation of the I/O's re-entrant semaphore implementation and
would not be an issue in the more general case.
Update:
One solution might be to used CONFIG_TLS, add the PID to struct
tls_info_s. Then the PID could be obtained without a system call.
Status: Open
Priority: Low-Medium. Right now, I do not know if these syscalls are a
real performance issue or not. The above statistics were collected
from a an atypical application (the OS test), and does an excessive
amount of console output. There is probably no issue with more typical
embedded applications.
Title: SECURITY ISSUES
Description: In the current designed, the kernel code calls into the user-space
allocators to allocate user-space memory. It is a security risk to
call into user-space in kernel-mode because that could be exploited
to gain control of the system. That could be fixed by dropping to
user mode before trapping into the memory allocators; the memory
allocators would then need to trap in order to return (this is
already done to return from signal handlers; that logic could be
renamed more generally and just used for a generic return trap).
Another place where the system calls into the user code in kernel
mode is work_usrstart() to start the user work queue. That is
another security hole that should be plugged.
Status: Open
Priority: Low (unless security becomes an issue).
Title: MICRO-KERNEL
Description: The initial kernel build cut many interfaces at a very high level.
The resulting monolithic kernel is then rather large. It would
not be a prohibitively large task to reorganize the interfaces so
that NuttX is built as a micro-kernel, i.e., with only the core
OS services within the kernel and with other OS facilities, such
as the file system, message queues, etc., residing in user-space
and to interfacing with those core OS facilities through traps.
Status: Open
Priority: Low. This is a good idea and certainly an architectural
improvement. However, there is no strong motivation now do
do that partitioning work.
Title: TIMER INTERRUPT CALLBACK
Description: The timer upper half driver at drivers/timers/timer.c performs
interrupt level callbacks into applications. This, of course,
will never work in anything but a non-secure, flat build.
Status: Open
Priority: Medium. The driver is only usable with all of its features
in a FLAT build.
Title: USER MODE TASKS CAN MODIFY PRIVILEGED TASKS
Description: Certain interfaces, such as sched_setparam(),
sched_setscheduler(), etc. can be used by user mode tasks to
modify the behavior of priviledged kernel threads.
task_delete() could even be used to kill a kernel thread.
For a truly secure system. Privileges need to be checked in
every interface that permits one thread to modify the
properties of another thread.
NOTE: It would be a simple matter to simply disable user
threads from modifying privileged threads. However, you
might also want to be able to modify privileged threads from
user tasks with certain permissions. Permissions is a much
more complex issue.
Status: Open
Priority: Low for most embedded systems but would be a critical need if
NuttX were used in a secure system.
o C++ Support
^^^^^^^^^^^
Title: USE OF SIZE_T IN NEW OPERATOR
Description: The argument of the 'new' operators should take a type of
size_t (see libxx/libxx_new.cxx and libxx/libxx_newa.cxx). But
size_t has an unknown underlying. In the nuttx sys/types.h
header file, size_t is typed as uint32_t (which is determined by
architecture-specific logic). But the C++ compiler may believe
that size_t is of a different type resulting in compilation errors
in the operator. Using the underlying integer type Instead of
size_t seems to resolve the compilation issues.
Status: Kind of open. There is a workaround. Setting CONFIG_CXX_NEWLONG=y
will define the operators with argument of type unsigned long;
Setting CONFIG_CXX_NEWLONG=n will define the operators with argument
of type unsigned int. But this is pretty ugly! A better solution
would be to get a hold of the compilers definition of size_t.
Priority: Low.
Title: STATIC CONSTRUCTORS AND MULTITASKING
Description: The logic that calls static constructors operates on the main
thread of the initial user application task. Any static
constructors that cache task/thread specific information such
as C streams or file descriptors will not work in other tasks.
See also UCLIBC++ AND STATIC CONSTRUCTORS below.
Status: Open
Priority: Low and probably will not changed. In these case, there will
need to be an application specific solution.
Title: UCLIBC++ AND STATIC CONSTRUCTORS
uClibc++ was designed to work in a Unix environment with
processes and with separately linked executables. Each process
has its own, separate uClibc++ state. uClibc++ would be
instantiated like this in Linux:
1) When the program is built, a tiny start-up function is
included at the beginning of the program. Each program has
its own, separate list of C++ constructors.
2) When the program is loaded into memory, space is set aside
for uClibc's static objects and then this special start-up
routine is called. It initializes the C library, calls all
of the constructors, and calls atexit() so that the destructors
will be called when the process exits.
In this way, you get a per-process uClibc++ state since there
is per-process storage of uClibc++ global state and per-process
initialization of uClibc++ state.
Compare this to how NuttX (and most embedded RTOSs) would work:
1) The entire FLASH image is built as one big blob. All of the
constructors are lumped together and all called together at
one time.
This, of course, does not have to be so. We could segregate
constructors by some criteria and we could use a task start
up routine to call constructors separately. We could even
use ELF executables that are separately linked and already
have their constructors separately called when the ELF
executable starts.
But this would not do you very much good in the case of
uClibc++ because:
2) NuttX does not support processes, i.e., separate address
environments for each task. As a result, the scope of global
data is all tasks. Any change to the global state made by
one task can effect another task. There can only one
uClibc++ state and it will be shared by all tasks. uClibc++
apparently relies on global instances (at least for cin and
cout) there is no way to to have any unique state for any
"task group".
[NuttX does not support processes because in order to have
true processes, your hardware must support a memory management
unit (MMU) and I am not aware of any mainstream MCU that has
an MMU (or, at least an MMU that is capable enough to support
processes).]
NuttX does not have processes, but it does have "task groups".
See http://www.nuttx.org/doku.php?id=wiki:nxinternal:tasksnthreads.
A task group is the task plus all of the pthreads created by
the task via pthread_create(). Resources like FILE streams
are shared within a task group. Task groups are like a poor
man's process.
This means that if the uClibc++ static classes are initialized
by one member of a task group, then cin/cout should work
correctly with all threads that are members of task group. The
destructors would be called when the final member of the task
group exists (if registered via atexit()).
So if you use only pthreads, uClibc++ should work very much like
it does in Linux. If your NuttX usage model is like one process
with many threads then you have Linux compatibility.
If you wanted to have uClibc++ work across task groups, then
uClibc++ and NuttX would need some extensions. I am thinking
along the lines of the following:
1) There is a per-task group storage are within the RTOS (see
include/nuttx/sched.h). If we add some new, non-standard APIs
then uClibc++ could get access to per-task group storage (in
the spirit of pthread_getspecific() which gives you access to
per-thread storage).
2) Then move all of uClibc++'s global state into per-task group
storage and add a uClibc++ initialization function that would:
a) allocate per-task group storage, b) call all of the static
constructors, and c) register with atexit() to perform clean-
up when the task group exits.
That would be a fair amount of effort. I don't really know what
the scope of such an effort would be. I suspect that it is not
large but probably complex.
NOTES:
1) See STATIC CONSTRUCTORS AND MULTITASKING
2) To my knowledge, only some uClibc++ ofstream logic is
sensitive to this. All other statically initialized classes
seem to work OK across different task groups.
Status: Open
Priority: Low. I have no plan to change this logic now unless there is
some strong demand to do so.
o Binary loaders (binfmt/)
^^^^^^^^^^^^^^^^^^^^^^^^
Title: NXFLAT TESTS
Description: Not all of the NXFLAT test under apps/examples/nxflat are working.
Most simply do not compile yet. tests/mutex runs okay but
outputs garbage on completion.
Update: 13-27-1, tests/mutex crashed with a memory corruption
problem the last time that I ran it.
Status: Open
Priority: High
Title: ARM UP_GETPICBASE()
Description: The ARM up_getpicbase() does not seem to work. This means
the some features like wdog's might not work in NXFLAT modules.
Status: Open
Priority: Medium-High
Title: NXFLAT READ-ONLY DATA IN RAM
Description: At present, all .rodata must be put into RAM. There is a
tentative design change that might allow .rodata to be placed
in FLASH (see Documentation/NuttXNxFlat.html).
Status: Open
Priority: Medium
Title: GOT-RELATIVE FUNCTION POINTERS
Description: If the function pointer to a statically defined function is
taken, then GCC generates a relocation that cannot be handled
by NXFLAT. There is a solution described in Documentation/NuttXNxFlat.html,
by that would require a compiler change (which we want to avoid).
The simple workaround is to make such functions global in scope.
Status: Open
Priority: Low (probably will not fix)
Title: USE A HASH INSTEAD OF A STRING IN SYMBOL TABLES
Description: In the NXFLAT symbol tables... Using a 32-bit hash value instead
of a string to identify a symbol should result in a smaller footprint.
Status: Open
Priority: Low
Title: WINDOWS-BASED TOOLCHAIN BUILD
Description: Windows build issue. Some of the configurations that use NXFLAT have
the linker script specified like this:
NXFLATLDFLAGS2 = $(NXFLATLDFLAGS1) -T$(TOPDIR)/binfmt/libnxflat/gnu-nxflat-gotoff.ld -no-check-sections
That will not work for windows-based tools because they require Windows
style paths. The solution is to do something like this:
if ($(WINTOOL)y)
NXFLATLDSCRIPT=${cygpath -w $(TOPDIR)/binfmt/libnxflat/gnu-nxflat-gotoff.ld}
else
NXFLATLDSCRIPT=$(TOPDIR)/binfmt/libnxflat/gnu-nxflat-gotoff.ld
endif
Then use
NXFLATLDFLAGS2 = $(NXFLATLDFLAGS1) -T"$(NXFLATLDSCRIPT)" -no-check-sections
Status: Open
Priority: There are too many references like the above. They will have
to get fixed as needed for Windows native tool builds.
Title: TOOLCHAIN COMPATIBILITY PROBLEM
Description: The older 4.3.3 compiler generates GOTOFF relocations to the constant
strings, like:
.L3:
.word .LC0(GOTOFF)
.word .LC1(GOTOFF)
.word .LC2(GOTOFF)
.word .LC3(GOTOFF)
.word .LC4(GOTOFF)
Where .LC0, LC1, LC2, LC3, and .LC4 are the labels corresponding to strings in
the .rodata.str1.1 section. One consequence of this is that .rodata must reside
in D-Space since it will addressed relative to the GOT (see the section entitled
"Read-Only Data in RAM" at
http://nuttx.org/Documentation/NuttXNxFlat.html#limitations).
The newer 4.6.3compiler generated PC relative relocations to the strings:
.L2:
.word .LC0-(.LPIC0+4)
.word .LC1-(.LPIC1+4)
.word .LC2-(.LPIC2+4)
.word .LC3-(.LPIC4+4)
.word .LC4-(.LPIC5+4)
This is good and bad. This is good because it means that .rodata.str1.1 can now
reside in FLASH with .text and can be accessed using PC-relative addressing.
That can be accomplished by simply moving the .rodata from the .data section to
the .text section in the linker script. (The NXFLAT linker script is located at
nuttx/binfmt/libnxflat/gnu-nxflat.ld).
This is bad because a lot of stuff may get broken an a lot of test will need to
be done. One question that I have is does this apply to all kinds of .rodata?
Or just to .rodata.str1.1?
Status: Open. Many of the required changes are in place but, unfortunately, not enough
go be fully functional. I think all of the I-Space-to-I-Space fixes are in place.
However, the generated code also includes PC-relative references to .bss which
just cannot be done.
Priority: Medium. The workaround for now is to use the older, 4.3.3 OABI compiler.
o Network (net/, drivers/net)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Title: LISTENING FOR UDP BROADCASTS
Description: Incoming UDP broadcast should only be accepted if listening on
INADDR_ANY(?)
Status: Open
Priority: Low
Title: CONCURRENT TCP SEND OPERATIONS
Description: At present, there cannot be two concurrent active TCP send
operations in progress using the same socket. This is because
the uIP ACK logic will support only one transfer at a time. The
solution is simple: A mutex will be needed to make sure that each
send that is started is able to be the exclusive sender until all of
the data to be sent has been ACKed.
Status: Open. There is some temporary logic to apps/nshlib that does
this same fix and that temporary logic should be removed when
send() is fixed.
Priority: Medium-Low. This is an important issue for applications that
send on the same TCP socket from multiple threads.
Title: POLL/SELECT ON TCP/UDP SOCKETS NEEDS READ-AHEAD
Description: poll()/select() only works for availability of buffered TCP/UDP
read data (when read-ahead is enabled). The way writing is
handled in the network layer, all sockets must wait when send and
cannot be notified when they can send without waiting.
Status: Open, probably will not be fixed.
Priority: Medium... this does effect porting of applications that expect
different behavior from poll()/select()
Title: SOCKETS DO NOT ALWAYS SUPPORT O_NONBLOCK
Description: sockets do not support all modes for O_NONBLOCK. Sockets
support nonblocking operations only (1) for TCP/IP non-
blocking read operations when read-ahead buffering is
enabled, (2) TCP/IP accept() operations when TCP/IP
connection backlog is enabled, (2) UDP/IP read() operations
when UDP read-ahead is enabled, and (3) non-blocking
operations on Unix domain sockets.
Status: Open
Priority: Low.
Title: UNFINISHED CRYSTALLAN CS89X0 DRIVER
Description: I started coding a CrystalLan CS89x0 driver (drivers/net/cs89x0.c),
but never finished it.
Status: Closed.
Priority: Low. I don't plan to finish the CS89x0 driver. It is just
history now. The unfinished coded is retained in case someone
needs to resurrect it.
Title: INTERFACES TO LEAVE/JOIN IGMP MULTICAST GROUP
Description: The interfaces used to leave/join IGMP multicast groups is non-standard.
RFC3678 (IGMPv3) suggests ioctl() commands to do this (SIOCSIPMSFILTER) but
also status that those APIs are historic. NuttX implements these ioctl
commands, but is non-standard because: (1) It does not support IGMPv3, and
(2) it looks up drivers by their device name (e.g., "eth0") vs IP address.
Linux uses setsockopt() to control multicast group membership using the
IP_ADD_MEMBERSHIP and IP_DROP_MEMBERSHIP options. It also looks up drivers
using IP addresses (It would require additional logic in NuttX to look up
drivers by IP address). See http://tldp.org/HOWTO/Multicast-HOWTO-6.html
Status: Open
Priority: Medium. All standards compatibility is important to NuttX. However, most
the mechanism for leaving and joining groups is hidden behind a wrapper
function so that little of this incompatibilities need be exposed.
Title: CLOSED CONNECTIONS IN THE BACKLOG
If a connection is backlogged but accept() is not called quickly, then
that connection may time out. How should this be handled? Should the
connection be removed from the backlog if it is times out or is closed?
Or should it remain in the backlog with a status indication so that accept()
can fail when it encounters the invalid connection?
Status: Open
Priority: Medium. Important on slow applications that will not accept
connections promptly.
Title: INTERRUPT LEVEL PROCESSING IN ETHERNET DRIVERS
Description: Too many Ethernet drivers do interrupt-level processing with
the network stack. The network stack supports either interrupt
level processing or normal task level processing (depending on
CONFIG_NET_NOINTS). This is really a very bad use of CPU
resources; All of the network stack processing should be
modified to use a work queue (and, all use of CONFIG_NET_NOINTS=n
should be eliminated). This applies to almost all Ethernet
drivers:
ARCHITECTURE CONFIG_NET_NOINTS? ADDRESS FILTER SUPPORT?
C5471 NO NO
STM32 YES YES
STM32F7 YES YES
TIVA ----------------------- ------
LM3S NO NO
TM4C YES YES
eZ80 NO NO
Kinetis YES YES (not tested)
LPC17xx YES YES (not tested)
LPC43xx YES YES (not tested)
DMxxx NIC NO NO
PIC32 NO NO
RGMP ??? ???
SAM3/4 YES YES
SAMA5D ----------------------- ------
EMACA NO YES (not tested)
EMACB YES YES
GMAC NO YES (not tested)
SAMV7 YES YES
SIM N/A (No interrupts) NO
The general outline of how this might be done is included in
drivers/net/skeleton.c
Status: Open
Priority: Pretty high if you want a well behaved system.
Title: UDP MULTICAST RECEPTION
Description: The logic in udp_input() expects either a single receive socket or
none at all. However, multiple sockets should be capable of
receiving a UDP datagram (multicast reception). This could be
handled easily by something like:
for (conn = NULL; conn = udp_active (pbuf, conn); )
If the callback logic that receives a packet responds with an
outgoing packet, then it will over-write the received buffer,
however. recvfrom() will not do that, however. We would have
to make that the rule: Recipients of a UDP packet must treat
the packet as read-only.
Status: Open
Priority: Low, unless your logic depends on that behavior.
Title: NETWORK WON'T STAY DOWN
Description: If you enable the NSH network monitor (CONFIG_NSH_NETINIT_MONITOR)
then the NSH 'ifdown' command is broken. Doing 'nsh> ifconfig eth0'
will, indeed, bring the network down. However, the network monitor
notices the change in the link status and will bring the network
back up. There needs to be some kind of interlock between
cmd_ifdown() and the network monitor thread to prevent this.
Status: Open
Priority: Low, this is just a nuisance in most cases.
Title: FIFO CLEAN-UP AFTER CLOSING UNIX DOMAIN DATAGRAM SOCKET
Description: FIFOs are used as the IPC underlying all local Unix domain
sockets. In NuttX, FIFOs are implemented as device drivers
(not as a special FIFO files). The FIFO device driver is
instantiated when the Unix domain socket communications begin
and will automatically be released when (1) the driver is
unlinked and (2) all open references to the driver have been
closed. But there is no mechanism in place now to unlink the
FIFO when the Unix domain datagram socket is no longer used.
The primary issue is timing.. the FIFO should persist until
it is no longer needed. Perhaps there should be a delayed
call to unlink() (using a watchdog or the work queue). If
the driver is re-opened, the delayed unlink could be
canceled? Needs more thought.
NOTE: This is not an issue for Unix domain streams sockets:
The end-of-life of the FIFO is well determined when sockets
are disconnected and support for that case is fully implemented.
Status: Open
Priority: Low for now because I don't have a situation where this is a
problem for me. If you use the same Unix domain paths, then
it is not a issue; in fact it is more efficient if the FIFO
devices persist. But this would be a serious problem if,
for example, you create new Unix domain paths dynamically.
In that case you would effectively have a memory leak and the
number of FIFO instances grow.
Title: TCP IPv4-MAPPED IPv6 ADDRESSES
Description: The UDP implementation in net/udp contains support for Hybrid
dual-stack IPv6/IPv4 implementations that utilize a special
class of addresses, the IPv4-mapped IPv6 addresses. You can
see that UDP implementation in:
udp_callback.c:
ip6_map_ipv4addr(ipv4addr,
udp_send.c:
ip6_is_ipv4addr((FAR struct in6_addr*)conn->u.ipv6.raddr)))
ip6_is_ipv4addr((FAR struct in6_addr*)conn->u.ipv6.raddr))
in_addr_t raddr = ip6_get_ipv4addr((FAR struct in6_addr*)conn->u.ipv6.raddr);
There is no corresponding support for TCP sockets.
Status: Open
Priority: Low. I don't know of any issues now, but I am sure that
someone will encounter this in the future.
Title: MISSING netdb INTERFACES
Description: There is no implementation for many netdb interfaces such as
getaddrinfo(), freeaddrinfo(), getnameinfo(), etc.
Status: Open
Priority: Low
o USB (drivers/usbdev, drivers/usbhost)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Title: USB STORAGE DRIVER DELAYS
Description: There is a workaround for a bug in drivers/usbdev/usbdev_storage.c.
that involves delays. This needs to be redesigned to eliminate these
delays. See logic conditioned on CONFIG_USBMSC_RACEWAR.
If queuing of stall requests is supported by the DCD then this workaround
is not required. In this case, (1) the stall is not sent until all
write requests preceding the stall request are sent, (2) the stall is
sent, and then after the stall is cleared, (3) all write requests
queued after the stall are sent.
See, for example, the queuing of pending stall requests in the SAM3/4
UDP driver at arch/arm/src/sam34/sam_udp.c. There the logic is do this
is implemented with a normal request queue, a pending request queue, a
stall flag and a stall pending flag:
1) If the normal request queue is not empty when the STALL request is
received, the stall pending flag is set.
2) If addition write requests are received while the stall pending flag
is set (or while waiting for the stall to be sent), those write requests
go into the pending queue.
3) When the normal request queue empties successful and all of the write
transfers complete, the STALL is sent. The stall pending flag is
cleared and the stall flag is set. Now the endpoint is really stalled.
4) After the STALL is cleared (via the Clear Feature SETUP), the pending
request queue is copied to the normal request queue, the stall flag is
cleared, and normal write request processing resumes.
Status: Open
Priority: Medium
Title: EP0 OUT CLASS DATA
Description: There is no mechanism in place to handle EP0 OUT data transfers.
There are two aspects to this problem, neither are easy to fix
(only because of the number of drivers that would be impacted):
1. The class drivers only send EP0 write requests and these are
only queued on EP0 IN by this drivers. There is never a read
request queued on EP0 OUT.
2. But EP0 OUT data could be buffered in a buffer in the driver
data structure. However, there is no method currently
defined in the USB device interface to obtain the EP0 data.
Updates: (1) The USB device-to-class interface as been extended so
that EP0 OUT data can accompany the SETUP request sent to the
class drivers. (2) The logic in the STM32 F4 OTG FS device driver
has been extended to provide this data. Updates are still needed
to other drivers.
Here is an overview of the required changes:
New two buffers in driver structure:
1. The existing EP0 setup request buffer (ctrlreq, 8 bytes)
2. A new EP0 data buffer to driver state structure (ep0data,
max packetsize)
Add a new state:
3. Waiting for EP0 setup OUT data (EP0STATE_SETUP_OUT)
General logic flow:
1. When an EP0 SETUP packet is received:
- Read the request into EP0 setup request buffer (ctrlreq,
8 bytes)
- If this is an OUT request with data length, set the EP0
state to EP0STATE_SETUP_OUT and wait to receive data on
EP0.
- Otherwise, the SETUP request may be processed now (or,
in the case of the F4 driver, at the conclusion of the
SETUP phase).
2. When EP0 the EP0 OUT DATA packet is received:
- Verify state is EP0STATE_SETUP_OUT
- Read the request into the EP0 data buffer (ep0data, max
packet size)
- Now process the previously buffered SETUP request along
with the OUT data.
3. When the setup packet is dispatched to the class driver,
the OUT data must be passed as the final parameter in the
call.
Update 2013-9-2: The new USB device-side driver for the SAMA5D3
correctly supports OUT SETUP data following the same design as
per above.
Update 2013-11-7: David Sidrane has fixed with issue with the
STM32 F1 USB device driver. Still a few more to go before this
can be closed out.
Status: Open
Priority: High for class drivers that need EP0 data. For example, the
CDC/ACM serial driver might need the line coding data (that
data is not used currently, but it might be).
Title: IMPROVED USAGE of STM32 USB RESOURCES
Description: The STM32 platforms use a non-standard, USB host peripheral
that uses "channels" to implement data transfers the current
logic associates each channel with an pipe/endpoint (with two
channels for bi-directional control endpoints). The OTGFS
peripheral has 8 channels and the OTGHS peripheral has 12
channels.
This works okay until you add a hub and try connect multiple
devices. A typical device will require 3-4 pipes and, hence,
4-5 channels. This effectively prevents using a hub with the
STM32 devices. This also applies to the EFM32 which uses the
same IP.
It should be possible to redesign the STM32 F4 OTGHS/OTGFS and
EFM32 host driver so that channels are dynamically assigned to
pipes as needed for individual transfers. Then you could have
more "apparent" pipes and make better use of channels.
Although there are only 8 or 12 channels, transfers are not
active all of the time on all channels so it ought to be
possible to have an unlimited number of "pipes" but with no
more than 8 or 12 active transfers.
Status: Open
Priority: Medium-Low
Title: USB CDC/ACM HOST CLASS DRIVER
Description: A CDC/ACM host class driver has been added. This has been
testing by running the USB CDC/ACM host on an Olimex
LPC1766STK and using the configs/stm3210e-eval/usbserial
configuration (using the CDC/ACM device side driver). There
are several unresolved issues that prevent the host driver
from being usable:
- The driver works fine when configured for reduced or bulk-
only protocol.
- Testing has not been performed with the interrupt IN channel
enabled (ie., I have not enabled FLOW control nor do I have
a test case that used the interrupt IN channel). I can see
that the polling for interrupt IN data is occurring
initially.
- I test for incoming data by doing 'nsh> cat /dev/ttyACM0' on
the Olimex LPC1766STK host. The bulk data reception still
works okay whether or not the interupt IN channel is enabled.
If the interrupt IN channel is enabled, then polling of that
channel appears to stop when the bulk in channel becomes
active.
- The RX reception logic uses the low priority work queue.
However, that logic never returns and so blocks other use of
the work queue thread. This is probably okay but means that
the RX reception logic probably should be moved to its own
dedicated thread.
- I get crashes when I run with the STM32 OTGHS host driver.
Apparently the host driver is trashing memory on receipt
of data.
- The SAMA5D EHCI and the LPC31 EHCI drivers both take semaphores
in the cancel method. The current CDC/ACM class driver calls
the cancel() method from an interrupt handler. This will
cause a crash. Those EHCI drivers should be redesigned to
permit cancellation from the interrupt level.
Most of these problems are unique to the Olimex LPC1766STK
DCD; some are probably design problems in the CDC/ACM host
driver. The bottom line is that the host CDC/ACM driver is
still immature and you could experience issues in some
configurations if you use it.
That all being said, I know of know no issues with the current
CDC/ACM driver if the interrupt IN endpoint is not used, i.e.,
in "reduced" mode. The only loss of functionality is output
flow control.
Status: Open
Priority: Medium-Low unless you really need host CDC/ACM support.
o Libraries (libc/)
^^^^^^^^^^^^^^^^^
Title: SIGNED time_t
Description: The NuttX time_t is type uint32_t. I think this is consistent
with all standards and with normal usage of time_t. However,
according to Wikipedia, time_t is usually implemented as a
signed 32-bit value.
Status: Open
Priority: Very low unless there is some compelling issue that I do not
know about.
Title: ENVIRON
Description: The definition of environ in stdlib.h is bogus and will not
work as it should. This is because the underlying
representation of the environment is not an array of pointers.
Status: Open
Priority: Medium
Title: TERMIOS
Description: Need some minimal termios support... at a minimum, enough to
switch between raw and "normal" modes to support behavior like
that needed for readline().
UPDATE: There is growing functionality in libc/termios/ and in the
ioctl methods of several MCU serial drivers (stm32, lpc43, lpc17,
pic32). However, as phrased, this bug cannot yet be closed since
this "growing functionality" does not address all termios.h
functionality and not all serial drivers support termios.
Status: Open
Priority: Low
Title: RESETTING GETOPT()
Description: There is an issue with the way that getopt() handles errors that
return '?'.
1. Does getopt() reset its global variables after returning '?' so
that it can be re-used? That would be required to support where
the caller terminates parsing before reaching the last parameter.
2. Or is the client expected to continue parsing after getopt()
returns '?' and parse until the final parameter?
The current getopt() implementation only supports #2.
Status: Open
Priority: Low
Title: CONCURRENT STREAM READ/WRITE
Description: NuttX only supports a single file pointer so reads and writes
must be from the same position. This prohibits implementation
of behavior like that required for fopen() with the "a+" mode.
According to the fopen man page:
"a+ Open for reading and appending (writing at end of file).
The file is created if it does not exist. The initial file
position for reading is at the beginning of the file, but
output is always appended to the end of the file."
At present, the single NuttX file pointer is positioned to the
end of the file for both reading and writing.
Status: Open
Priority: Medium. This kind of operation is probably not very common in
deeply embedded systems but is required by standards.
Title: DIVIDE BY ZERO
Description: This is bug 3468949 on the SourceForge website (submitted by
Philipp Klaus Krause):
"lib_strtod.c does contain divisions by zero in lines 70 and 96.
AFAIK, unlike for Java, division by zero is not a reliable way to
get infinity in C. AFAIK compilers are allowed e.g. give a compile-
time error, and some, such as sdcc, do. AFAIK, C implementations
are not even required to support infinity. In C99 the macro isinf()
could replace the first use of division by zero. Unfortunately, the
macro INFINITY from math.h probably can't replace the second division
by zero, since it will result in a compile-time diagnostic, if the
implementation does not support infinity."
Status: Open
Priority:
Title: OLD dtoa NEEDS TO BE UPDATED
Description: This implementation of dtoa in libc/stdio is old and will not
work with some newer compilers. See
http://patrakov.blogspot.com/2009/03/dont-use-old-dtoac.html
Status: Open
Priority: ??
Title: FLOATING POINT FORMATS
Description: Only the %f floating point format is supported. Others are accepted
but treated like %f.
Status: Open
Priority: Medium (this might important to someone).
Title: FLOATING POINT PRECISION
Description: A fieldwidth and precision is required with the %f format. If %f
is used with no format, than floating numbers will be printed with
a precision of 0 (effectively presented as integers).
Status: Open
Priority: Medium (this might important to someone).
Title: LIBM INACCURACIES
Description: "..if you are writing something like robot control or
inertial navigation system for aircraft, I have found
that using the toolchain libmath is only safe option.
I ported some code for converting quaternions to Euler
angles to NuttX for my project and only got it working
after switching to newlib math library.
"NuttX does not fully implement IEC 60559 floating point
from C99 (sections marked [MX] in OpenGroup specs) so if
your code assumes that some function, say pow(), actually
behaves right for all the twenty or so odd corner cases
that the standards committees have recently specified,
you might get surprises. I'd expect pow(0.0, 1.0) to
return 0.0 (as zero raised to any positive power is
well-defined in mathematics) but I get +Inf.
"NuttX atan2(-0.0, -1.0) returns +M_PI instead of correct
-M_PI. If we expect [MX] functionality, then atan2(Inf, Inf)
should return M_PI/4, instead NuttX gives NaN.
"asin(2.0) does not set domain error or return NaN. In fact
it does not return at all as the loop in it does not
converge, hanging your app.
"There are likely many other issues like these as the Rhombus
OS code has not been tested or used that much. Sorry for not
providing patches, but we found it easier just to switch the
math library."
Ref: https://groups.yahoo.com/neo/groups/nuttx/conversations/messages/7805
UPDATE: 2015-09-01: A fix for the noted problems with asin()
has been applied.
2016-07-30: Numerous fixes and performance improvements from
David Alessio.
Status: Open
Priority: Low for casual users but clearly high if you need care about
these incorrect corner case behaviors in the math libraries.
o File system / Generic drivers (fs/, drivers/)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
NOTE: The NXFFS file system has its own TODO list at nuttx/fs/nxffs/README.txt
Title: CHMOD(), TRUNCATE(), AND FSTAT()
Description: Implement chmod(), truncate(), and fstat().
Status: Open
Priority: Low
Title: ROMFS CHECKSUMS
Description: The ROMFS file system does not verify checksums on either
volume header on on the individual files.
Status: Open
Priority: Low. I have mixed feelings about if NuttX should pay a
performance penalty for better data integrity.
Title: SPI-BASED SD MULTIPLE BLOCK TRANSFERS
Description: The simple SPI based MMCS/SD driver in fs/mmcsd does not
yet handle multiple block transfers.
Status: Open
Priority: Medium-Low
Title: SDIO-BASED SD READ-AHEAD/WRITE BUFFERING INCOMPLETE
Description: The drivers/mmcsd/mmcsd_sdio.c driver has hooks in place to
support read-ahead buffering and write buffering, but the logic
is incomplete and untested.
Status: Open
Priority: Low
Title: POLLHUP SUPPORT
Description: All drivers that support the poll method should also report
POLLHUP event when the driver is closed.
Status: Open
Priority: Medium-Low
Title: CONFIG_RAMLOG_CONSOLE DOES NOT WORK
Description: When I enable CONFIG_RAMLOG_CONSOLE, the system does not come up
properly (using configuration stm3240g-eval/nsh2). The problem
may be an assertion that is occurring before we have a console.
Status: Open
Priority: Medium
Title: UNIFIED DESCRIPTOR REPRESENTATION
Description: There are two separate ranges of descriptors for file and
socket descriptors: if a descriptor is in one range then it is
recognized as a file descriptor; if it is in another range
then it is recognized as a socket descriptor. These separate
descriptor ranges can cause problems, for example, they makes
dup'ing descriptors with dup2() problematic. The two groups
of descriptors are really indices into two separate tables:
On an array of file structures and the other an array of
socket structures. There really should be one array that
is a union of file and socket descriptors. Then socket and
file descriptors could lie in the same range.
Another example of how the current implementation limits
functionality: I recently started an implement of the FILEMAX
(using pctl() instead sysctl()). My objective was to be able
to control the number of available file descriptors on a task-
by-task basis. The complexity due to the partitioning of
desciptor space in a range for file descriptors and a range
for socket descriptors made this feature nearly impossible to
implement.
Status: Open
Priority: Low
Title: DUPLICATE FAT FILE NAMES
Description: "The NSH and POSIX API interpretations about sensitivity or
insensitivity to upper/lowercase file names seem to be not
consistent in our usage - which can result in creating two
directories with the same name..."
Example using NSH:
nsh> echo "Test1" >/tmp/AtEsT.tXt
nsh> echo "Test2" >/tmp/aTeSt.TxT
nsh> ls /tmp
/tmp:
AtEsT.tXt
aTeSt.TxT
nsh> cat /tmp/aTeSt.TxT
Test2
nsh> cat /tmp/AtEsT.tXt
Test1
Status: Open
Priority: Low
Title: FAT LONG FILENAME COMPATIBILITY
Description: Recently there have been reports that file with long file
names created by NuttX don't have long file names when viewed
on Windows. The long file name support has been around for a
long time and I don't ever having seen this before so I am
suspecting that some evil has crept in.
Status: Open
Priority: Medium
Title: MISSING FILES IN NSH 'LS' OF A DIRECTORY
Description: I have seen cases where (1) long file names are enabled,
but (2) a short file name is created like:
nsh> echo "This is another test" >/mnt/sdcard/another.txt
But then on subsequent 'ls' operations, the file does not appear:
nsh> ls -l /mnt/sdcard
I have determined that the problem is because, for some as-
of-yet-unkown reason the short file name is treated as a long
file name. The name then fails the long filename checksum
test and is skipped.
readdir() (and fat_readdir()) is the logic underlying the
failure and the problem appears to be something unique to the
fat_readdir() implementation. Why? Because the file is
visible when you put the SD card on a PC and because this
works fine:
nsh> ls -l /mnt/sdcard/another.txt
The failure does not happen on all short file names. I do
not understand the pattern. But I have not had the opportunity
to dig into this deeply.
Status: Open
Priority: Perhaps not a problem??? I have analyzed this problem and
I am not sure what to do about it. I am suspected that a
fat filesystem was used with a version of NuttX that does
not support long file name entries. Here is the failure
scenario:
1) A file with a long file name is created under Windows.
2) Then the file is deleted. I am not sure if Windows or
NuttX deleted the file, but the resulting directory
content is not compatible with NuttX with long file
name support.
The file deletion left the full sequence of long
file name entries intact but apparently delete only
the following short file name entry. I am thinking
that this might have happened because a version of NuttX
with only short file name support was used to delete
the file.
3) When a new file with a short file name was created, it
re-used the short file name entry that was previously
deleted. This makes the new short file name entry
look like a part of the long file name.
4) When comparing the checksum in the long file name
entry with the checksum of the short file name, the
checksum fails and the entire directory sequence is
ignored by readder() logic. This the file does not
appear in the 'ls'.
o Graphics subsystem (graphics/)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
See also the NxWidgets TODO list file for related issues.
Title: UNTESTED GRAPHICS APIS
Description: Testing of all APIs is not complete. See
http://nuttx.sourceforge.net/NXGraphicsSubsystem.html#testcoverage
Status: Open
Priority: Medium
Title: ITALIC FONTS / NEGATIVE FONT OFFSETS
Description: Font metric structure (in include/nuttx/nx/nxfont.h) should allow
negative X offsets. Negative x-offsets are necessary for certain
glyphs (and is very common in italic fonts).
For example Eth, icircumflex, idieresis, and oslash should have
offset=1 in the 40x49b font (these missing negative offsets are
NOTE'ed in the font header files).
Status: Open. The problem is that the x-offset is an unsigned bitfield
in the current structure.
Priority: Low.
Title: RAW WINDOW AUTORAISE
Description: Auto-raise only applies to NXTK windows. Shouldn't it also apply
to raw windows as well?
Status: Open
Priority: Low
Title: AUTO-RAISE DISABLED
Description: Auto-raise is currently disabled in NX multi-server mode. The
reason is complex:
- Most touchscreen controls send touch data a high rates
- In multi-server mode, touch events get queued in a message
queue.
- The logic that receives the messages performs the auto-raise.
But it can do stupid things after the first auto-raise as
it operates on the stale data in the message queue.
I am thinking that auto-raise ought to be removed from NuttX
and moved out into a graphics layer (like NxWM) that knows
more about the appropriate context to do the autoraise.
Status: Open
Priority: Medium low
Title: IMPROVED NxTERM FONT CACHING
Description: Now each NxTerm instance has its own private font cache
whose size is determined by CONFIG_NXTERM_MXCHARS. If there
are multiple NxTerm instances using the same font, each will
have a separate font cache. This is inefficient and wasteful
of memory: Each NxTerm instance should share a common font
cache.
Status: Open
Priority: Medium. Not important for day-to-day testing but would be
a critical improvement if NxTerm were to be used in a
product.
Title: NxTERM VT100 SUPPORT
Description: If the NxTerm will be used with the Emacs-like command line
editor (CLE), then it will need to support VT100 cursor control
commands.
Status: Open
Priority: Low, the need has not yet arisen.
Title: PER-WINDOW FRAMEBUFFERS
Description: One of the most awkward things to handle in the NX windowing
system is the re-draw callback. This is difficult because it
requires ad hoc, custom logic to be able to do the redrawing
in most cases.
One solution would be to provide a per-window framebuffer.
All rending would be performed into the per-window framebuffer
and the rended bits would be copied the LCD or framebuffer
device memory on demand when the redraw is required.
This would (a) greatly simplify the graphics interface, (b)
greatly improve redraw performance, and (c) enable a more
generic use of the windowing. The downside would be a large
usage of memory to hold all of the framebuffers, one for each
window.
Status: Open
Priority: Low, of mostly strategic value.
Title: VERTICAL ANTI-ALIASING
Description: Anti-aliasing is implemented along the horizontal raster line
with fractional pixels at the ends of each line. There is no
accounting for fractional pixels in the vertical direction.
As a result lines closer to vertical receive better anti-
aliasing than lines closer to horizontal.
Status: Open
Priority: Low, not a serious issue but worth noting. There is no plan
to change this behavior.
o Build system
^^^^^^^^^^^^
Title: MAKE EXPORT LIMITATIONS
Description: The top-level Makefile 'export' target that will bundle up all of the
NuttX libraries, header files, and the startup object into an export-able
tarball. This target uses the tools/mkexport.sh script. Issues:
1. This script assumes the host archiver ar may not be appropriate for
non-GCC toolchains
2. For the kernel build, the user libraries should be built into some
libuser.a. The list of user libraries would have to accepted with
some new argument, perhaps -u.
Status: Open
Priority: Low.
Title: NATIVE WINDOWS BUILD BROKEN
Description: The way that apps/ now generates Kmenu files depends on changes added
to apps/tools/mkkconfig.sh. Similar changes need to be made to
apps/tools/mkkconfig.bat to restore the Windows Native build.
UPDATE: The mkkconfig.bat script has been updated and appears to work.
A native build has still not been attempted and there could likely be
issues the carriage returns in Kconfig files. There are also some
issues the interpreters/ficl and bas directories during 'make menuconfig'
that still need to be investigated.
Status: Open
Priority: Low, since I am not aware of anyone using the Windows Native build.
But, of course, very high if you want to use it.
o Other drivers (drivers/)
^^^^^^^^^^^^^^^^^^^^^^^^
o Linux/Cywgin simulation (arch/sim)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Title: SIMULATOR HAS NO INTERRUPTS (NON-PREMPTIBLE)
Description: The current simulator implementation is has no interrupts and, hence,
is non-preemptible. Also, without simulated interrupt, there can
be no high-fidelity simulated device drivers.
Currently, all timing and serial input is simulated in the IDLE loop:
When nothing is going on in the simulation, the IDLE loop runs and
fakes timer and UART events.
Status: Open
Priority: Low, unless there is a need for developing a higher fidelity simulation
I have been thinking about how to implement simulated interrupts in
the simulation. I think a solution would work like this:
http://www.nuttx.org/doku.php?id=wiki:nxinternal:simulator
Title: ROUND-ROBIN SCHEDULING IN THE SIMULATOR
Description: Since the simulation is not pre-emptible, you can't use round-robin
scheduling (no time slicing). Currently, the timer interrupts are
"faked" during IDLE loop processing and, as a result, there is no
task pre-emption because there are no asynchronous events. This could
probably be fixed if the "timer interrupt" were driver by Linux
signals. NOTE: You would also have to implement up_irq_save() and
up_irq_restore() to block and (conditionally) unblock the signal.
Status: Open
Priority: Low
Title: SMP SIMULATION ISSUES
Description: The configuration has basic support SMP testing. The simulation
supports the emulation of multiple CPUs by creating multiple
pthreads, each run a copy of the simulation in the same process
address space.
At present, the SMP simulation is not fully functional: It does
operate on the simulated CPU threads for a few context switches
then fails during a setjmp() operation. I suspect that this is
not an issue with the NuttX SMP logic but more likely some chaos
in the pthread controls. I have seen similar such strange behavior
other times that I have tried to use setjmp/longmp from a signal
handler! Like when I tried to implement simulated interrupts
using signals.
Apparently, if longjmp is invoked from the context of a signal
handler, the result is undefined:
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1318.htm
You can enable SMP for ostest configuration by enabling:
-# CONFIG_EXPERIMENTAL is not set
+CONFIG_EXPERIMENTAL=y
+CONFIG_SPINLOCK=y
+CONFIG_SMP=y
+CONFIG_SMP_NCPUS=2
+CONFIG_SMP_IDLETHREAD_STACKSIZE=2048
You also must enable near-realtime-performance otherwise even long
timeouts will expire before a CPU thread even has a chance to
execute.
-# CONFIG_SIM_WALLTIME is not set
+CONFIG_SIM_WALLTIME=y
And you can enable some additional debug output with:
-# CONFIG_DEBUG_SCHED is not set
+CONFIG_DEBUG_SCHED=y
-# CONFIG_SCHED_INSTRUMENTATION is not set
+CONFIG_SCHED_INSTRUMENTATION=y
The NSH configuration can also be forced to run SMP, but
suffers from the same quirky behavior. I can be made
reliable if you modify arch/sim/src/up_idle.c so that
the IDLE loop only runs for CPU0. Otherwise, often
simuart_post() will be called from CPU1 and it will try
to restart NSH on CPU0 and, again, the same quirkiness
occurs.
But for example, this command:
nsh> sleep 1 &
will execute the sleep command on CPU1 which has worked
every time that I have tried it (which is not too many
times).
Status: Open
Priority: Low, SMP is important, but SMP on the simulator is not
o ARM (arch/arm/)
^^^^^^^^^^^^^^^
Title: IMPROVED ARM INTERRUPT HANDLING
Description: ARM interrupt handling performance could be improved in some
ways. One easy way is to use a pointer to the context save
area in g_current_regs instead of using up_copystate so much.
This approach is already implemented for the ARM Cortex-M0,
Cortex-M3, Cortex-M4, and Cortex-A5 families. But still needs
to be back-ported to the ARM7 and ARM9 (which are nearly
identical to the Cortex-A5 in this regard). The change is
*very* simple for this architecture, but not implemented.
Status: Open. But complete on all ARM platforms except ARM7 and ARM9.
Priority: Low.
Title: IMPROVED ARM INTERRUPT HANDLING
Description: The ARM and Cortex-M3 interrupt handlers restores all registers
upon return. This could be improved as well: If there is no
context switch, then the static registers need not be restored
because they will not be modified by the called C code.
(see arch/sh/src/sh1/sh1_vector.S for example)
Status: Open
Priority: Low
Title: CORTEX-M3 STACK OVERFLOW
Description: There is bit bit logic in up_fullcontextrestore() that executes on
return from interrupts (and other context switches) that looks like:
ldr r1, [r0, #(4*REG_CPSR)] /* Fetch the stored CPSR value */
msr cpsr, r1 /* Set the CPSR */
/* Now recover r0 and r1 */
ldr r0, [sp]
ldr r1, [sp, #4]
add sp, sp, #(2*4)
/* Then return to the address at the stop of the stack,
* destroying the stack frame
*/
ldr pc, [sp], #4
Under conditions of excessively high interrupt conditions, many
nested interrupts can occur just after the 'msr cpsr' instruction.
At that time, there are 4 bytes on the stack and, with each
interrupt, the stack pointer may increment and possibly overflow.
This can happen only under conditions of continuous interrupts.
See this email thread: https://groups.yahoo.com/neo/groups/nuttx/conversations/messages/1261
On suggested change is:
ldr r1, [r0, #(4*REG_CPSR)] /* Fetch the stored CPSR value */
msr spsr_cxsf, r1 /* Set the CPSR */
ldmia r0, {r0-r15}^
But this has not been proven to be a solution.
UPDATE: Other ARM architectures have a similar issue.
Status: Open
Priority: Low. The conditions of continuous interrupts is really the problem.
If your design needs continuous interrupts like this, please try
the above change and, please, submit a patch with the working fix.
Title: IMPROVED TASK START-UP AND SYSCALL RETURN
Description: Couldn't up_start_task and up_start_pthread syscalls be
eliminated. Wouldn't this work to get us from kernel-
to user-mode with a system trap:
lda r13, #address
str rn, [r13]
msr spsr_SVC, rm
ld r13,{r15}^
Would also need to set r13_USER and r14_USER. For new
SYS_context_switch... couldn't we do he same thing?
Also... System calls use traps to get from user- to kernel-
mode to perform OS services. That is necessary to get from
user- to kernel-mode. But then another trap is used to get
from kernel- back to user-mode. It seems like this second
trap should be unnecessary. We should be able to do the
same kind of logic to do this.
Status: Open
Priority: Low-ish, but a good opportunity for performance improvement.
o Network Utilities (apps/netutils/)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Title: UNVERIFIED THTTPD FEATURES
Description: Not all THTTPD features/options have been verified. In particular, there is no
test case of a CGI program receiving POST input. Only the configuration of
apps/examples/thttpd has been tested.
Status: Open
Priority: Medium
Title: THTTPD WARNINGS
Description: If the network is enabled, but THTTPD is not configured, it spews out lots
of pointless warnings. This is kind of annoying and unprofessional; needs to
be fixed someday.
Status: Open. An annoyance, but not a real problem.
Priority: Low
Title: NETWORK MONITOR NOT GENERALLY AVAILABLE
Description: The NSH network management logic has general applicability
but is currently useful only because it is embedded in the NSH
module. It should be moved to apps/system or, better,
apps/netutils.
Status: Open
Priority: Low
o NuttShell (NSH) (apps/nshlib)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Title: IFCONFIG AND MULTIPLE NETWORK INTERFACES
Description: The ifconfig command will not behave correctly if an interface
is provided and there are multiple interfaces. It should only
show status for the single interface on the command line; it will
still show status for all interfaces.
Status: Open
Priority: Low
Title: ARPPING COMMAND
Description: Add an arping command
Status: Open
Priority: Low (enhancement)
o System libraries apps/system (apps/system)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Title: READLINE IMPLEMENTATION
Description: readline implementation does not use C-buffered I/O, but rather
talks to serial driver directly via read(). It includes VT-100
specific editing commands. A more generic readline() should be
implemented using termios' tcsetattr() to put the serial driver
into a "raw" mode.
Status: Open
Priority: Low (unless you are using mixed C-buffered I/O with readline and
fgetc, for example).
o Pascal Add-On (pcode/)
^^^^^^^^^^^^^^^^^^^^^^
Title: P-CODES IN MEMORY UNTESTED
Description: Need APIs to verify execution of P-Code from memory buffer.
Status: Open
Priority: Low
Title: SMALLER LOADER AND OBJECT FORMAT
Description: Loader and object format may be too large for some small
memory systems. Consider ways to reduce memory footprint.
Status: Open
Priority: Medium
Title: PDBG
Description: Move the the pascal p-code debugger into the NuttX apps/ tree
where it can be used from the NSH command line.
Status: Open
Priority: Low
o Other Applications & Tests (apps/examples/)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Title: EXAMPLES/PIPE ON CYGWIN
Description: The redirection test (part of examples/pipe) terminates
incorrectly on the Cywgin-based simulation platform (but works
fine on the Linux-based simulation platform).
Status: Open
Priority: Low
Title: EXAMPLES/SENDMAIL UNTESTED
Description: examples/sendmail is untested on the target (it has been tested
on the host, but not on the target).
Status: Open
Priority: Med
Title: EXAMPLES/NX FONT CACHING
Description: The font caching logic in examples/nx is incomplete. Fonts are
added to the cache, but never removed. When the cache is full
it stops rendering. This is not a problem for the examples/nx
code because it uses so few fonts, but if the logic were
leveraged for more general purposes, it would be a problem.
Update: see examples/nxtext for some improved font cache handling.
Status: Open
Priority: Low. This is not really a problem because examples/nx works
fine with its bogus font caching.
Title: EXAMPLES/NXTEXT ARTIFACTS
Description: examples/nxtext. Artifacts when the pop-up window is opened.
There are some artifacts that appear in the upper left hand
corner. These seems to be related to window creation. At
tiny artifact would not be surprising (the initial window
should like at (0,0) and be of size (1,1)), but sometimes
the artifact is larger.
Status: Open
Priority: Medium.
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