NuttX TODO List (Last updated February 24, 2021) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 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 board ports. See also the individual README.txt files in the boards/ sub-directories for issues related to each board port. nuttx/: (16) Task/Scheduler (sched/) (2) SMP (1) Memory Management (mm/) (0) Power Management (drivers/pm) (5) Signals (sched/signal, arch/) (2) pthreads (sched/pthread, libs/libc/pthread) (0) Message Queues (sched/mqueue) (1) Work Queues (sched/wqueue) (6) Kernel/Protected Build (2) C++ Support (5) Binary loaders (binfmt/) (17) Network (net/, drivers/net) (4) USB (drivers/usbdev, drivers/usbhost) (2) Other drivers (drivers/) (9) Libraries (libs/libc/, libs/libm/) (11) File system/Generic drivers (fs/, drivers/) (10) Graphics Subsystem (graphics/) (1) Build system / Toolchains (2) Linux/Cygwin simulation (arch/sim) (5) ARM (arch/arm/) apps/ and other Add-Ons: (1) Network Utilities (apps/netutils/) (1) NuttShell (NSH) (apps/nshlib) (2) System libraries apps/system (apps/system) (1) Modbus (apps/modbus) (5) 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? This behavior was implemented as an options controlled by the configuration setting CONFIG_SCHED_EXIT_KILL_CHILDREN. This option must be used with caution, however. It should not be used unless you are certain of what you are doing. Uninformed of this option can often lead to memory leaks since, for example, memory allocations held by threads are not automatically freed! Status: Closed. No, this behavior will not be implemented unless specifically selected. Priority: Medium, required for good emulation of process/pthread model. The current behavior allows for the main thread of a task to exit() and any child pthreads will persist. That does raise some issues: The main thread is treated much like just-another- pthread but must follow the semantics of a task or a process. That results in some inconsistencies (for example, with robust mutexes, what should happen if the main thread exits while holding a mutex?) Title: pause() NON-COMPLIANCE Description: In the POSIX description of this function the pause() function must 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: https://nuttx.apache.org/docs/latest/components/paging.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 boards/arm/lpc31xx/ea3131/configs/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(), on_exit(), AND pthread_cleanup_pop() 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? 4. In the case of task_delete() and pthread_cancel() without deferred cancellation, these callbacks will run on the thread of execution and address context of the caller of task_delete() or pthread_cancel(). That is very bad! The fix for all of these issues it to have the callbacks run on the caller's thread as is currently done with signal handlers. Signals are delivered differently in PROTECTED and KERNEL modes: The delivery involves a signal handling trampoline function in the user address space and two signal handlers: One to call the signal handler trampoline in user mode (SYS_signal_handler) and on in with the signal handler trampoline to return to supervisor mode (SYS_signal_handler_return) The primary difference is in the location of the signal handling trampoline: - In PROTECTED mode, there is on a single user space blob with a header at the beginning of the block (at a well- known location. There is a pointer to the signal handler trampoline function in that header. - In the KERNEL mode, a special process signal handler trampoline is used at a well-known location in every process address space (ARCH_DATA_RESERVE->ar_sigtramp). 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 tls_errno field from struct tls_info_s to struct task_group_s. However, I am still not sure if this should be done or not. NOTE: glibc behaves this way unless __thread is defined then, in that case, it behaves like NuttX (using TLS to save the thread local errno). Status: Closed. The existing solution is better and compatible with thread-aware GLIBC (although its incompatibilities could show up in porting some code). I will retain this issue for reference only. Priority: N/A 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 an 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. Title: INTERNAL VERSIONS OF USER FUNCTIONS Description: The internal NuttX logic uses the same interfaces as does the application. That sometime produces a problem because there is "overloaded" functionality in those user interfaces that are not desirable. For example, having cancellation points hidden inside of the OS can cause non-cancellation point interfaces to behave strangely. Here is another issue:  Internal OS functions should not set errno and should never have to look at the errno value to determine the cause of the failure.  The errno is provided for compatibility with POSIX application interface requirements and really doesn't need to be used within the OS. Both of these could be fixed if there were special internal versions these functions.  For example, there could be a an nxsem_wait() that does all of the same things as sem_wait() was does not create a cancellation point and does not set the errno value on failures. Everything inside the OS would use nx_sem_wait(). Applications would call sem_wait() which would just be a wrapper around nx_sem_wait() that adds the cancellation point and that sets the errno value on failures. On particularly difficult issue is the use of common memory manager C, and NX libraries in the build. For the PROTECTED and KERNEL builds, this issue is resolved. In that case, The OS links with a different version of the libraries than does the application: The OS version would use the OS internal interfaces and the application would use the standard interfaces. But for the FLAT build, both the OS and the applications use the same library functions. For applications, the library functions *must* support errno's and cancellation and, hence, these are also used within the OS. But that raises yet another issue: If the application version of the libraries use the standard interfaces internally, then they may generate unexpected cancellation points. For example, the memory management would take a semaphore using sem_wait() to get exclusive access to the heap. That means that every call to malloc() and free() would be a cancellation point, a clear POSIX violation. Changes like that could clean up some of this internal craziness. UPDATE: 2017-10-03: This change has been completed for the case of semaphores used in the OS. Still need to checkout signals and messages queues that are also used in the OS. Also backed out commit b4747286b19d3b15193b2a5e8a0fe48fa0a8638c. 2017-10-06: This change has been completed for the case of signals used in the OS. Still need to checkout messages queues that are also used in the OS. 2017-10-10: This change has been completed for the case of message queue used in the OS. I am keeping this issue open because (1) there are some known remaining calls that that will modify the errno (such as dup(), dup2(), nxtask_activate(), kthread_create(), exec(), mq_open(), mq_close(), and others) and (2) there may still be calls that create cancellation points. Need to check things like open(), close(), read(), write(), and possibly others. 2018-01-30: This change has been completed for the case of scheduler functions used within the OS: sched_getparam(), sched_setparam(), sched_getscheduler(), sched_setschedule(), and sched_setaffinity(), 2018-09-15: This change has been completed for the case of open() used within the OS. There are places under libs/ and boards/ that have not been converted. I also note cases where fopen() is called under libs/libc/netdb/. 2019-09-11: built_isavail() no longer sets the errno variable. Status: Open Priority: Low. Things are working OK the way they are. But the design could be improved and made a little more efficient with this change. Task: IDLE THREAD TCB SETUP Description: There are issues with setting IDLE thread stacks: The problem is colorizing that stack to use with stack usage monitoring logic. There is logic in some start functions to do this in a function called go_nx_start. It is available in these architectures: ./arm/src/efm32/efm32_start.c:static void go_nx_start(void *pv, unsigned int nbytes) ./arm/src/kinetis/kinetis_start.c:static void go_nx_start(void *pv, unsigned int nbytes) ./arm/src/sam34/sam_start.c:static void go_nx_start(void *pv, unsigned int nbytes) ./arm/src/samv7/sam_start.c:static void go_nx_start(void *pv, unsigned int nbytes) ./arm/src/stm32/stm32_start.c:static void go_nx_start(void *pv, unsigned int nbytes) ./arm/src/stm32f7/stm32_start.c:static void go_nx_start(void *pv, unsigned int nbytes) ./arm/src/stm32l4/stm32l4_start.c:static void go_nx_start(void *pv, unsigned int nbytes) ./arm/src/tms570/tms570_boot.c:static void go_nx_start(void *pv, unsigned int nbytes) ./arm/src/xmc4/xmc4_start.c:static void go_nx_start(void *pv, unsigned int nbytes) But no others. Status: Open Priority: Low, only needed for more complete debug. Title: PRIORITY INHERITANCE WITH SPORADIC SCHEDULER Description: The sporadic scheduler manages CPU utilization by a task by alternating between a high and a low priority. In either state, it may have its priority boosted. However, under some circumstances, it is impossible in the current design to switch to the correct priority if a semaphore held by the sporadic thread is participating in priority inheritance: There is an issue when switching from the high to the low priority state. If the priority was NOT boosted above the higher priority, it still may still need to boosted with respect to the lower priority. If the highest priority thread waiting on a semaphore held by the sporadic thread is higher in priority than the low priority but less than the higher priority, then new thread priority should be set to that middle priority, not to the lower priority. In order to do this we would need to know the highest priority from among all tasks waiting for the all semaphores held by the sporadic task. That information could be retained by the priority inheritance logic for use by the sporadic scheduler. The boost priority could be retained in a new field of the TCB (say, pend_priority). That pend_priority could then be used when switching from the higher to the lower priority. Status: Open Priority: Low. Does anyone actually use the sporadic scheduler? Title: SIMPLIFY SPORADIC SCHEDULER DESIGN Description: I have been planning to re-implement sporadic scheduling for some time. I believe that the current implementation is unnecessarily complex. There is no clear statement for the requirements of sporadic scheduling that I could find, so I based the design on some behaviors of another OS that I saw published (QNX as I recall). But I think that the bottom line requirement for sporadic scheduling is that is it should make a best attempt to control a fixed percentage of CPU bandwidth for a task in during an interval only by modifying it is priority between a low and a high priority. The current design involves several timers: A "budget" timer plus a variable number of "replenishment" timers and a lot of nonsense to duplicate QNX behavior that I think I not necessary. It think that the sporadic scheduler could be re-implemented with only the single "budget" timer. Instead of starting a new "replenishment" timer when the task is resumed, that single timer could just be extended. Status: Open Priority: Low. This is an enhancement. And does anyone actually use the sporadic scheduler? Title: REMOVE NESTED CANCELLATION POINT SUPPORT Description: The current implementation support nested cancellation points. The TCB field cpcount keeps track of that nesting level. However, cancellation points should not be calling other cancellation points so this design could be simplified by removing all support for nested cancellation points. Status: Open Priority: Low. No harm is being done by the current implementation. This change is primarily for aesthetic reasons. If would reduce memory usage by a very small but probably insignificant amount. Title: DAEMONIZE ELF PROGRAM Description: It is a common practice to "daemonize" to detach a task from its parent. This is used with NSH, for example, so that NSH will not stall, waiting in waitpid() for the child task to exit. Daemonization is done to creating a new task which continues to run while the original task exits (sending the SIGCHLD signal to the parent and awakening waitpid()). In a pure POSIX system, this is down with fork(), perhaps like: if (fork() != 0) { exit(); } but is usually done with task_create() in NuttX. But when task_create() is called from within an ELF program, a very perverse situation is created: The basic problem involves address environments and task groups: "Task groups" are emulations of Linux processes. For the case of the FLAT, ELF module, the address environment is allocated memory that contains the ELF module. When you call task_create() from the ELF program, you now have two task groups running in the same address environment. That is a perverse situation for which there is no standard solution. There is nothing comparable to that. Even in Linux, fork() creates another address environment (although it is an exact copy of the original). When the ELF program was created, the function exec() in binfmt/binfmt_exec.c runs. It sets up a call back that will be invoked when the ELF program exits. When ELF program exits, the address environment is destroyed and the other task running in the same address environment is then running in stale memory and will eventually crash. Nothing special happens when the other created task running in the allocated address environment exits since has no such call backs. In order to make this work you would need logic like: 1. When the ELF task calls task_create(), it would need to: a. Detect that task_create() was called from an ELF program, b. increment a reference count on the address environment, and c. Set up the same exit hook for the newly created task. 2. Then when either the ELF program task or the created task in the same address environment exits, it would decrement the reference count. When the last task exits, the reference count would go to zero and the address environment could be destroyed. This is complex work and would take some effort and probably requires redesign of existing code and interfaces to get a proper, clean, modular solution. Status: Open Priority: Medium-Low. A simple work-arounds when using NSH is to use the '&' postfix to put the started ELF program into background. o SMP ^^^ Title: MISUSE OF sched_lock() IN SMP MODE Description: The OS API sched_lock() disables pre-emption and locks a task in place. In the single CPU case, it is also often used to enforce a simple critical section since not other task can run while pre-emption is locked. This, however, does not generalize to the SMP case. In the SMP case, there are multiple tasks running on multiple CPUs. The basic behavior is still correct: The task that has locked pre-emption will not be suspended. However, there is no longer any protection for use as a critical section: tasks running on other CPUs may still execute that unprotected code region. The solution is to replace the use of sched_lock() with stronger protection such as spin_lock_irqsave(). Status: Open Priority: Medium for SMP system. Not critical to single CPU systems. NOTE: There are no known bugs from this potential problem. Title: ISSUES WITH ACCESSING CPU INDEX Description: The CPU number is accessed usually with the macro this_cpu(). The returned CPU number is then used for various things, typically as an array index. However, if pre-emption is not disabled,then it is possible that a context switch could occur and that logic could run on another CPU with possible fatal consequences. We need to evaluate all use of this_cpu() and assure that it is used in a way that guarantees the the code continues to execute on the same CPU. Status: Open Prioity: Medium. This is a logical problem but I have never seen an bugs caused by this. But I believe that failures are possible. 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 exits. 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. NOTE: This applies to the FLAT and PROTECTED builds only. There is no such leaking of memory in the KERNEL build mode. Priority: Medium/Low, a good feature to prevent memory leaks but would have negative impact on memory usage and code size. o Power Management (drivers/pm) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ o Signals (sched/signal, arch/) ^^^^^^^^^^^^^^^^^^^^^^^ Title: STANDARD SIGNALS Description: 'Standard' signals and signal actions are not fully supported. The SIGCHLD signal is supported and, if the option CONFIG_SIG_DEFAULT=y is included, some signals will perform their default actions (dependent upon addition configuration settings): Signal Action Additional Configuration ------- -------------------- ------------------------- SIGUSR1 Abnormal Termination CONFIG_SIG_SIGUSR1_ACTION SIGUSR2 Abnormal Termination CONFIG_SIG_SIGUSR2_ACTION SIGALRM Abnormal Termination CONFIG_SIG_SIGALRM_ACTION SIGPOLL Abnormal Termination CONFIG_SIG_SIGPOLL_ACTION SIGSTOP Suspend task CONFIG_SIG_SIGSTOP_ACTION SIGTSTP Suspend task CONFIG_SIG_SIGSTOP_ACTION SIGCONT Resume task CONFIG_SIG_SIGSTOP_ACTION SIGINT Abnormal Termination CONFIG_SIG_SIGKILL_ACTION SIGKILL Abnormal Termination CONFIG_SIG_SIGKILL_ACTION 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 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 libs/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. Title: NO QUEUING of SIGNAL ACTIONS Description: In the architecture specific implementation of struct xcptcontext, there are fields used by signal handling logic to pass the state information needed to dispatch signal actions to the appropriate handler. There is only one copy of this state information in the implementations of struct xcptcontext and, as a consequence, if there is a signal handler executing on a thread, then addition signal actions will be lost until that signal handler completes and releases those resources. Status: Open Priority: Low. This design flaw has been around for ages and no one has yet complained about it. Apparently the visibility of the problem is very low. Title: QUEUED SIGNAL ACTIONS ARE INAPPROPRIATELY DEFERRED Description: The implement of nxsig_deliver() does the following in a loop: - It takes the next next queued signal action from a list - Calls the architecture-specific up_sigdeliver() to perform the signal action (through some sleight of hand in up_schedule_sigaction()) - up_sigdeliver() is a trampoline function that performs the actual signal action as well as some housekeeping functions then - up_sigdeliver() performs a context switch back to the normal, uninterrupted thread instead of returning to nxsig_deliver(). The loop in nxsig_deliver() then will have the opportunity to run until when that normal, uninterrupted thread is suspended. Then the loop will continue with the next queued signal action. Normally signals execute immediately. The is the whole reason why almost all blocking APIs return when a signal is received (with errno equal to EINTR). Status: Open Priority: Low. This design flaw has been around for ages and no one has yet complained about it. Apparently the visibility of the problem is very low. o pthreads (sched/pthreads libs/libc/pthread) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Title: PTHREAD_PRIO_PROTECT Description: Extend pthread_mutexattr_setprotocol(). It should support PTHREAD_PRIO_PROTECT (and so should its non-standard counterpart sem_setproto()). "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 (https://apache.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." Title: INAPPROPRIATE USE OF sched_lock() BY pthreads Description: In implementation of standard pthread functions, the non- standard, NuttX function sched_lock() is used. This is very strong since it disables pre-emption for all threads in all task groups. I believe it is only really necessary in most cases to lock threads in the task group with a new non- standard interface, say pthread_lock(). This is because the OS resources used by a thread such as mutexes, condition variable, barriers, etc. are only meaningful from within the task group. So, in order to performance exclusive operations on these resources, it is only necessary to block other threads executing within the task group. This is an easy change: pthread_lock() and pthread_unlock() would simply operate on a semaphore retained in the task group structure. I am, however, hesitant to make this change: In the FLAT build model, there is nothing that prevents people from accessing the inter-thread controls from threads in different task groups. Making this change, while correct, might introduce subtle bugs in code by people who are not using NuttX correctly. Status: Open Priority: Low. This change would improve real-time performance of the OS but is not otherwise required. o Message Queues (sched/mqueue) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ o Work Queues (sched/wqueue) ^^^^^^^^^^^^^^^^^^^^^^^^^^ Title: WORK QUEUE DELAY INACCURACIES Description: Each queued work may have an optional delay value associated with it. That delay should be respect to the time that the work is queued. However, since we do not know the time the work is queue, the actual delay will be respect to the time that the work is processed. Under certain conditions, the work may sit in the queue for some time before it is processed, leading to an inaccuracy in the delay. One solution might involved saving the time when in the work structure when the work is queued. Then the delay logic can take the difference between the processing time and the queued time to get a more accurate delay. Status: Open Priority: In all known use cased, the priority is low. A problem is would only occur if the work queue is overload or if work in the work queue suspends waiting for a resource (both of which are much bigger problems). o Kernel/Protected Build ^^^^^^^^^^^^^^^^^^^^^^ 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. This getpid() call is part of the re-entrant semaphore logic used with printf() and other C buffered I/O. 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, boards////kernel/up_userspace.c, libs/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 use TLS, add the PID to struct tls_info_s. Then the PID could be obtained without a system call. TLS is not very useful in the FLAT build, however. TLS works by putting per-thread data at the bottom of an aligned stack. The current stack pointer is then ANDed with the alignment mask to obtain the per-thread data address. There are problems with this in the FLAT and PROTECTED builds: First the maximum size of the stack is limited by the number of bits in the mask. This means that you need to have a very high alignment to support tasks with large stacks. But secondly, the higher the alignment of the stacks stacks, the more memory is lost to fragmentation. In the KERNEL build, the the stack lies at a virtual address and it is possible to have highly aligned stacks with no such penalties. 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: 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 privileged kernel threads. 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. task_delete(), for example, is not permitted to kill a kernel thread. But should not a privileged user task be able to do so? Status: Open Priority: Low for most embedded systems but would be a critical need if NuttX were used in a secure system. Title: SIGNAL ACTION VULNERABILITY Description: When a signal action is performed, the user stack is used. Unlike Linux, applications do not have separate user and supervisor stacks; everything is done on the user stack. In the implementation of up_sigdeliver(), a copy of the register contents that will be restored is present on the stack and could be modified by the user application. Thus, if the user mucks with the return stack, problems could occur when the user task returns to supervisor mode from the the signal handler. A recent commit (3 Feb 2019) does protect the status register and return address so that a malicious task cannot change the return address or switch to supervisor mode. Other register are still modifiable so there is other possible mayhem that could be done. A better solution, in lieu of a kernel stack, would be to eliminate the stack-based register save area altogether and, instead, save the registers in another, dedicated state save area in the TCB. The only hesitation to this option is that it would significantly increase the size of the TCB structure and, hence, the per-thread memory overhead. Status: Open Priority: Medium-ish if are attempting to make a secure environment that may host malicious code. Very low for the typical FLAT build, however. o C++ Support ^^^^^^^^^^^ 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 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 https://cwiki.apache.org/confluence/display/NUTTX/Tasks+vs.+Threads+FAQ. 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 ($(CONFIG_CYGWIN_WINTOOL),y) NXFLATLDSCRIPT=${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. 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, UNBUFFERED TCP SEND OPERATIONS Description: At present, there cannot be two concurrent active TCP send operations in progress using the same socket *unless* CONFIG_TCP_WRITE_BUFFER. This is because the uIP ACK logic will support only one transfer at a time. Such a situation could occur if explicit TCP send operations are performed using the same socket (or dup's of the same) socket on two different threads. It can also occur implicitly when you execute more than one thread over and NSH Telenet session. There are two possible solutions: 1. Remove option to build the network without write buffering enabled. This is is simplest and perhaps the best option. Certainly a system can be produced with a smaller RAM footprint without write buffering. However, that probably does not justify permitted a crippled system. 2. Another option is to serialize the non-buffered writes for a socket with a mutex. i.e., add a mutex 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. That can be a very significant delay involving the send, waiting for the ACK or a timeout and possible retransmissions! Although it uses more memory, I believe that option 1 is the better solution and will avoid difficult TCP bugs in the future. Status: Open. Priority: Medium-Low. This is only an important issue for people who use multi-threaded, unbuffered TCP networking without a full understanding of the issues. 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, either (1) If CONFIG_UDP/TCP_WRITE_BUFFERS=y then we never have to wait to send; otherwise, we always have to wait to send. So it is impossible to notify the caller when it can send without waiting. An exception "never having to wait" is the case where we are out of memory for use in write buffering. In that case, the blocking send()/sendto() would have to wait for the memory to become available. Status: Open, probably will not be fixed. Priority: Medium... this does effect porting of applications that expect different behavior from poll()/select() 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: IPv6 REQUIRES ADDRESS FILTER SUPPORT Description: IPv6 requires that the Ethernet driver support NuttX address filter interfaces. Several Ethernet drivers do support there, however. Others support the address filtering interfaces but have never been verified: C5471, LM3S, ez80, DM0x90 NIC, PIC, LPC54: Do not support address filtering. Kinetis, LPC17xx, LPC43xx: Untested address filter support Status: Open Priority: Pretty high if you want a to use IPv6 on these platforms. 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 getnetbyname(), getprotobyname(), getnameinfo(), etc. Status: Open Priority: Low Title: ETHERNET WITH MULTIPLE LPWORK THREADS Description: Recently, Ethernet drivers were modified to support multiple work queue structures. The question was raised: "My only reservation would be, how would this interact in the case of having CONFIG_STM32_ETHMAC_LPWORK and CONFIG_SCHED_LPNTHREADS > 1? Can it be guaranteed that one work item won't be interrupted and execution switched to another? I think so but am not 100% confident." I suspect that you right. There are probably vulnerabilities in the CONFIG_STM32_ETHMAC_LPWORK with CONFIG_SCHED_LPNTHREADS > 1 case. But that really doesn't depend entirely upon the change to add more work queue structures. Certainly with only work queue structure you would have concurrent Ethernet operations in that multiple LP threads; just because the work structure is available, does not mean that there is not dequeued work in progress. The multiple structures probably widens the window for that concurrency, but does not create it. The current Ethernet designs depend upon a single work queue to serialize data. In the case of multiple LP threads, some additional mechanism would have to be added to enforce that serialization. NOTE: Most drivers will call net_lock() and net_unlock() around the critical portions of the driver work. In that case, all work will be properly serialized. This issue only applies to drivers that may perform operations that require protection outside of the net_lock'ed region. Sometimes, this may require extending the netlock() to be beginning of the driver work function. Status: Open Priority: High if you happen to be using Ethernet in this configuration. Title: NETWORK DRIVERS USING HIGH PRIORITY WORK QUEUE Description: Many network drivers run the network on the high priority work queue thread (or support an option to do so). Networking should not be done on the high priority work thread because it interferes with real-time behavior. Fix by forcing all network drivers to run on the low priority work queue. Status: Open Priority: Low. Not such big deal for demo network test and demo configurations except that it provides a bad example for a product OS configuration. Title: REPARTITION DRIVER FUNCTIONALITY Description: Every network driver performs the first level of packet decoding. It examines the packet header and calls ipv4_input(), ipv6_input(). icmp_input(), etc. as appropriate. This is a maintenance problem because it means that any changes to the network input interfaces affects all drivers. A better, more maintainable solution would use a single net_input() function that would receive all incoming packets. This function would then perform that common packet decoding logic that is currently implemented in every network driver. Status: Open Priority: Low. Really just as aesthetic maintainability issue. Title: BROADCAST WITH MULTIPLE NETWORK INTERFACES Description: There is currently no mechanism to send a broadcast packet out through several network interfaces. Currently packets can be sent to only one device. Logic in netdev_findby_ipvXaddr() currently just selects the first device in the list of devices; only that device will receive broadcast packets. Status: Open Priority: High if you require broadcast on multiple networks. There is no simple solution known at this time, however. Perhaps netdev_findby_ipvXaddr() should return a list of devices rather than a single device? All upstream logic would then have to deal with a list of devices. That would be a huge effect and certainly doesn't dount as a "simple solution". Title: ICMPv6 FOR 6LoWPAN Description: The current ICMPv6 and neighbor-related logic only works with Ethernet MAC. For 6LoWPAN, a new more conservative IPv6 neighbour discovery is provided by RFC 6775. This RFC needs to be supported in order to support ping6 on a 6LoWPAN network. If RFC 6775 were implemented, then arbitrary IPv6 addresses, including addresses from DHCPv6 could be used. UPDATE: With IPv6 neighbor discovery, any IPv6 address may be associated with any short or extended address. In fact, that is the whole purpose of the neighbor discover logic: It plays the same role as ARP in IPv4; it ultimately just manages a neighbor table that, like the arp table, provides the mapping between IP addresses and node addresses. The NuttX, Contiki-based 6LoWPAN implementation circumvented the need for the neighbor discovery logic by using only MAC- based addressing, i.e., the lower two or eight bytes of the IP address are the node address. Most of the 6LoWPAN compression algorithms exploit this to compress the IPv6 address to nothing but a bit indicating that the IP address derives from the node address. So I think IPv6 neighbor discover is useless in the current implementation. If we want to use IPv6 neighbor discovery, we could dispense with the all MAC based addressing. But if we want to retain the more compact MAC-based addressing, then we don't need IPv6 neighbor discovery. So, the full neighbor discovery logic is not currently useful, but it would still be nice to have enough in place to support ping6. Full neighbor support would probably be necessary if we wanted to route 6LoWPAN frames outside of the WPAN. Status: Open Priority: Low for now. I don't plan on implementing this. It would only be relevant if we were to decide to abandon the use of MAC-based addressing in the 6LoWPAN implementation. Title: ETHERNET LOCAL BROADCAST DOES NOT WORK Description: In case of "local broadcast" the system still send ARP request to the destination, but it shouldn't, it should broadcast. For Example, the system has network with IP 10.0.0.88, netmask of 255.255.255.0, it should send messages for 10.0.0.255 as broadcast, and not send ARP for 10.0.0.255 For more easier networking, the next line should have give me the broadcast address of the network, but it doesn't: ioctl(_socket_fd, SIOCGIFBRDADDR, &bc_addr); Status: Open Priority: Medium Title: TCP ISSUES WITH QUICK CLOSE Description: This failure has been reported in the accept() logic: - psock_tcp_accept() waits on net_lockedwait() below - The accept operation completes, the socket is in the connected state and psock_accept() is awakened. It cannot run, however, because its priority is low and so it is blocked from execution. - In the mean time, the remote host sends a packet which is presumably caught in the read-ahead buffer. - Then the remote host closes the socket. Nothing happens on the target side because net_start_monitor() has not yet been called. - Then accept() finally runs, but not with a connected but rather with a disconnected socket. This fails when it attempts to start the network monitor on the disconnected socket below. - It is also impossible to read the buffered TCP data from a disconnected socket. The TCP recvfrom() logic would also need to permit reading buffered data from a disconnected socket. This problem was report when the target hosted an FTP server and files were being accessed by FileZilla. connect() most likely has this same issue. A work-around might be to raise the priority of the thread that calls accept(). accept() might also need to check the tcpstateflags in the connection structure before returning in order to assure that the socket truly is connected. Status: Open Priority: Medium. I have never heard of this problem being reported before, so I suspect it might not be so prevalent as one might expect. Title: LOCAL DATAGRAM RECVFROM RETURNS WRONG SENDER ADDRESS Description: The recvfrom logic for local datagram sockets returns the incorrect sender "from" address. Instead, it returns the receiver's "to" address. This means that returning a reply to the "from" address receiver sending a packet to itself. Status: Open Priority: Medium High. This makes using local datagram sockets in anything but a well-known point-to-point configuration impossible. 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 boards/arm/stm32/stm3210e-eval/configs/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 on the Olimex LPC1766STK. - 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 interrupt 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. UPDATE: This behavior needs to be retested with: commit ce2845c5c3c257d081f624857949a6afd4a4668a Author: Janne Rosberg Date: Tue Mar 7 06:58:32 2017 -0600 usbhost_cdcacm: fix tx outbuffer overflow and remove now invalid assert commit 3331e9c49aaaa6dcc3aefa6a9e2c80422ffedcd3 Author: Janne Rosberg Date: Tue Mar 7 06:57:06 2017 -0600 STM32 OTGHS host: stm32_in_transfer() fails and returns NAK if a short transfer is received. This causes problems from class drivers like CDC/ACM where short packets are expected. In those protocols, any transfer may be terminated by sending short or NUL packet. commit 0631c1aafa76dbaa41b4c37e18db98be47b60481 Author: Gregory Nutt Date: Tue Mar 7 07:17:24 2017 -0600 STM32 OTGFS, STM32 L4 and F7: Adapt Janne Rosberg's patch to STM32 OTGHS host to OTGFS host, and to similar implements for L4 and F7. - 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 no issues with the current CDC/ACM driver on the Olimex LPC1766STK platform if the interrupt IN endpoint is not used, i.e., in "reduced" mode. The only loss of functionality is output flow control. UPDATE: The CDC/ACM class driver may also now be functional on the STM32. That needs to be verified. Status: Open Priority: Medium-Low unless you really need host CDC/ACM support. o Libraries (libs/libc/, libs/libm/) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 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 libs/libc/termios/ and in the ioctl methods of several MCU serial drivers (stm32, lpc43, lpc17, pic32, and others). 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: 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 libs/libc/stdio is old and will not work with some newer compilers. See http://patrakov.blogspot.com/2009/03/dont-use-old-dtoac.html Update: A new dtoa version is not available and enabled with CONFIG_NANO_PRINF. However, the old version of dtoa is still in in place and lib_libvsprintf() has been dupliated. I think this issue should remain open until the implementations have been unified. Status: Open Priority: ?? Title: FLOATING POINT FORMATS Description: Only the %f floating point format is supported. Others are accepted but treated like %f. Update: %g is supported with CONFIG_NANO_PRINTF. 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." 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. Title: REPARTITION LIBC FUNCTIONALITY Description: There are many things implemented within the kernel (for example under sched/pthread) that probably should be migrated in the C library where it belongs. I would really like to see a little flavor of a micro-kernel at the OS interface: I would like to see more primitive OS system calls with more higher level logic in the C library. One awkward thing is the incompatibility of KERNEL vs FLAT builds: In the kernel build, it would be nice to move many of the thread-specific data items out of the TCB and into the process address environment where they belong. It is difficult to make this compatible with the FLAT build, however. Status: Open Priority: Low o File system / Generic drivers (fs/, drivers/) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ NOTE: The NXFFS file system has its own TODO list at nuttx/fs/nxffs/README.txt Title: MISSING FILE SYSTEM FEATURES Description: Implement missing file system features: chmod() is probably not relevant since file modes are not currently supported. File privileges would also be good to support. But this is really a small part of a much larger feature. NuttX has no user IDs, there are no groups, there are no privileges associated with either. User's don't need credentials. This is really a system wide issues of which chmod is only a small part. User privileges never seemed important to me since NuttX is intended for deeply embedded environments where there are not multiple users with varying levels of trust. link, unlink, softlink, readlink - For symbolic links. Only the ROMFS file system currently supports hard and soft links, so this is not too important. The top-level, pseudo-file system supports soft links. File locking Special files - NuttX support special files only in the top- level pseudo file system. Unix systems support many different special files via mknod(). This would be important only if it is an objective of NuttX to become a true Unix OS. Again only supported by ROMFS. True inodes - Standard Unix inodes. Currently only supported by ROMFs. File times, for example as set by utimes(). The primary obstacle to all these is that each would require changes to all existing file systems. That number is pretty large. The number of file system implementations that would need to be reviewed and modified As of this writing this would include binfs, fat, hostfs, nfs, nxffs, procfs, romfs, tmpfs, unionfs, plus pseduo-file system support. 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: 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: 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-unknown 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 readdir() logic. This is why the file does not appear in the 'ls'. Title: SILENT SPIFFS FILE TRUNCATION Description: Under certain corner case conditions, SPIFFS will truncate files. All of the writes to the file will claim that the data has been written but after the file is closed, it may be a little shorter than expected. This is due to how the caching is implemented in SPIFFS: 1. On each write, the data is not written to the FLASH but rather to an internal cache in memory. 2. When the a write causes the cache to become full, the content of cache is flushed to memory. If that flush fails because the FLASH has become full, write will return the file system full error (ENOSPC). 3. The cache is also flushed when the file is closed (or when fsync() is called). These will also fail if the file system becomes full. The problem is when the file is closed, the final file size could be smaller than the number of successful writes to the file. This error is probably not so significant in a real world file system usage: It requires that you write continuously to SPIFFS, never deleting files or freeing FLASH resources in any way. And it requires the unlikely circumstance that the final file written has its last few hundred bytes in cache when the file is closed but there are even fewer bytes available on the FLASH. That would be rare with a cache size of a few hundred bytes and very large serial FLASH. This issue does cause the test at apps/testing/fstest to fail. That test fails with a "Partial Read" because the file being read is smaller than number bytes written to the file. That test does write small files continuously until file system is full and even the the error is rare. The boards/sim/sim/sim/configs/spiffs test can used to demonstrate the error. Status: Open Priority: Medium. It is certain a file system failure, but I think that the exposure in real world uses cases is very small. Title: FAT: CAN'T SEEK TO END OF FILE IF READ-ONLY Description: If the size of the underlying file is an exact multiple of the FAT cluster size, then you cannot seek to the end of the file if the file was opened read-only. In that case, the FAT lseek logic will return ENOSPC. This is because seeking to the end of the file involves seeking to an offset that is the size of the file (number of bytes allocated for file + 1). In order to seek to a position, the current FAT implementation insists that there be allocated file space at the seek position. Seeking beyond the end of the file has the side effect of extending the file. [NOTE: This automatic extension of the file cluster allocation is probably unnecessary and another issue of its own.] For example, suppose you have a cluster size that is 4096 bytes and a file that is 8192 bytes long. Then the file will consist of 2 allocated clusters at offsets 0 through 8191. If the file is opened O_RDWR or O_WRONLY, then the statement: offset = lseek(fd, 0, SET_SEEK); will seek to offset 8192 which beyond the end of the file so a new (empty) cluster will be added. Now the file consists of three clusters and the file position refers to the first byte of the third cluster. If the file is open O_RDONLY, however, then that same lseek statement will fail. It is not possible to seek to position 8192. That is beyond the end of the allocated cluster chain and since the file is read-only, it is not permitted to extend the cluster chain. Hence, the error ENOSPC is returned. This code snippet will duplicate the problem. It assumes a cluster size of 512 and that /tmp is a mounted FAT file system: #define BUFSIZE 1024 //8192, depends on cluster size static char buffer[BUFSIZE]; #if defined(BUILD_MODULE) int main(int argc, FAR char *argv[]) #else int hello_main(int argc, char *argv[]) #endif { ssize_t nwritten; off_t pos; int fd; int ch; int i; for (i = 0, ch = ' '; i < BUFSIZE; i++) { buffer[i] = ch; if (++ch == 0x7f) { ch = ' '; } } fd = open("/tmp/testfile", O_WRONLY | O_CREAT | O_TRUNC, 0644); if (fd < 0) { printf("open failed: %d\n", errno); return 1; } nwritten = write(fd, buffer, BUFSIZE); if (nwritten < 0) { printf("write failed: %d\n", errno); return 1; } close(fd); fd = open("/tmp/testfile", O_RDONLY); if (fd < 0) { printf("open failed: %d\n", errno); return 1; } pos = lseek(fd, 0, SEEK_END); if (pos < 0) { printf("lseek failed: %d\n", errno); return 1; } else if (pos != BUFSIZE) { printf("lseek failed: %d\n", pos); return 1; } close(fd); return 0; } Status: Open Priority: Medium. Although this is a significant design error, the problem has existed for 11 years without being previously reported. I conclude, then that the exposure from this problem is not great. Why would you seek to the end of a file using a read=only file descriptor anyway? Only one reason I can think of: To get the size of the file. The alternative (and much more efficient) way to do that is via stat(). 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. 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: 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: 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. Title: WIDE-FONT SUPPORT Description: Wide fonts are not currently supported by the NuttX graphics sub- system. Status: Open Priority: Low for many, but I imagine higher in countries that use wide fonts Title: LOW-RES FRAMEBUFFER RENDERING Description: There are obvious issues in the low-res, < 8 BPP, implementation of the framebuffer rendering logic of graphics/nxglib/fb. I see two obvious problems in reviewing nxglib_copyrectangle(): 1. The masking logic might work 1 BPP, but is insufficient for other resolutions like 2-BPP and 4-BPP. 2. The use of lnlen will not handle multiple bits per pixel. It would need to be converted to a byte count. The function PDC_copy_glyph() in the file apps/graphics/pdcurs34/nuttx/pdcdisp.c derives from nxglib_copyrectangle() and all of those issues have been resolved in that file. Other framebuffer rendering functions probably have similar issues. Status: Open Priority: Low. It is not surprising that there would be bugs in this logic: I have never encountered a hardware framebuffer with sub-byte pixel depth. If such a beast ever shows up, then this priority would be higher. Title: INCOMPLATE PLANAR COLOR SUPPORT Description: The original NX design included support for planar colors, i.e,. for devices that provide separate framebuffers for each color component. Planar graphics hard was common some years back but is rarely encountered today. In fact, I am not aware of any MCU that implements planar framebuffers. Support for planar colors is, however, unverified and incomplete. In fact, many recent changes explicitly assume a single color plane: Planar colors are specified by a array of components; some recent logic uses only component [0], ignoring the possible existence of other color component frames. Completely removing planar color support is one reasonable options; it is not likely that NuttX will encounter planar color hardware and this would greatly simplify the logic and eliminate inconsistencies in the immplementation. Status: Open Priority: Low. There is no problem other than one of aesthetics. 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. o Other drivers (drivers/) ^^^^^^^^^^^^^^^^^^^^^^^^ Title: SYSLOG OUTPUT LOST ON A CRASH Description: Flush syslog output on crash. I don't know how to do in the character driver case with interrupts disabled. It would be easy to flush the interrupt interrupt buffer, but not the data buffered within a character driver (such as the serial driver). Perhaps there could be a crash dump IOCTL command to flush that buffered data with interrupts disabled? Status: Open Priority: Low. It would be a convenience and would simplify crash debug if you could see all of the SYSLOG output up to the time of the crash. But not essential. Title: SERIAL DRIVER WITH DMA DOES NOT DISCARD OOB CHARACTERS Description: If Ctrl-Z or Ctrl-C actions are enabled, the the OOB character that generates the signal action must not be placed in the serial driver Rx buffer. This behavior is correct for the non-DMA case (serial_io.c), but not for the DMA case (serial_dma.c). In the DMA case, the OOB character is left in the Rx buffer and will be received as normal Rx data by the application. It should not work that way. Perhaps in the DMA case, the OOB characters could be filtered out later, just before returning the Rx data to the application? Status: Open Priority: Low, provided that the application can handle these characters in the data stream. o Linux/Cygwin 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: https://cwiki.apache.org/confluence/display/NUTTX/NuttX+Simulation 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 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/renesas/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. One 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. Title: USE COMMON VECTOR LOGIC IN ALL ARM ARCHITECTURES. Description: Originally, each ARMv7-M MCU architecture had its own private implementation for interrupt vectors and interrupt handling logic. This was superseded by common interrupt vector logic but these private implementations were never removed from older MCU architectures. This is turning into a maintenance issue because any improvements to the common vector handling must also be re-implemented for each of the older MCU architectures. Status: Open Priority: Low. A pain in the ass and an annoying implementation, but not really an issue otherwise. 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 o NuttShell (NSH) (apps/nshlib) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ See some NHS issues under "Kernel/Protected Build" as well. 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 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). 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: - usbmsc_configure - Called from apps/system/usbmsc and apps/system/composite - usbmsc_bindlun - Called from apps/system/usbmsc - usbmsc_exportluns - Called from apps/system/usbmsc. Status: Open Priority: Medium/High -- the kernel build configuration is not fully fielded yet. o Modbus (apps/modbus) ^^^^^^^^^^^^^^^^^^^^ Title: MODBUS NOT USABLE WITH USB SERIAL Description: Modbus can be used with USB serial, however, if the USB serial connection is lost, Modbus will hang in an infinite loop. This is a problem in the handling of select() and read() and could probably resolved by studying the Modbus error handling. A more USB-friendly solution would be to: (1) Re-connect and (2) re-open the serial drivers. That is what is done is NSH. When the serial USB device is removed, this terminates the session and NSH will then try to re-open the USB device. See the function nsh_waitusbready() in the file apps/nshlib/nsh_usbconsole.c. When the USB serial is reconnected the open() in the function will succeed and a new session will be started. Status: Open Priority: Low. This is really an enhancement request: Modbus was never designed to work with removable serial devices. o Other Applications & Tests (apps/examples/) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Title: EXAMPLES/PIPE ON CYGWIN Description: The redirection test (part of examples/pipe) terminates incorrectly on the Cygwin-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. Update: The NXTERM font cache has been generalized and is now offered as the standard, common font cache for all applications. both the nx and nxtext examples should be modified to use this common font cache. See interfaces defined in nxfonts.h. 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. Title: ILLEGAL CALLS TO romdisk_register() Description: Several examples (and other things under apps/) make illegal calls to romdisk_register(). This both violates the portable POSIX OS interface and makes these applications un-usable in PROTECTED and KERNEL build modes. Non-compliant examples include: examples/bastest, examples/elf, examples/module, examples/nxflat, examples/posix_spawn, examples/romfs, examples/sotest, examples/thttpd, examples/unionfs These examples are simple demos and, hence, you could argue that it is not so bad that they violate the interface for the purpose of demonstration (although they do set a bad example because of this). These examples should, of course, use boardctl(BOARDIOC_ROMDISK) to create the ROM disk instead of calling romdisk_register() directly. Status: Open Priority: Medium.