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NuttX TODO List (Last updated January 14, 2013)
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This file summarizes known NuttX bugs, limitations, inconsistencies with
standards, things that could be improved, and ideas for enhancements.
(10) Task/Scheduler (sched/)
(1) Memory Managment (mm/)
(3) Signals (sched/, arch/)
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(2) pthreads (sched/)
(6) Binary loaders (binfmt/)
(17) Network (net/, drivers/net)
(4) USB (drivers/usbdev, drivers/usbhost)
(12) Libraries (libc/, )
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(9) File system/Generic drivers (fs/, drivers/)
(5) Graphics subystem (graphics/)
(5) Linux/Cywgin simulation (arch/sim)
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(6) ARM (arch/arm/)
(2) ARM/i.MX (arch/arm/src/imx/)
(7) ARM/LPC214x (arch/arm/src/lpc214x/)
(0) ARM/LPC43x (arch/arm/src/lpc43xx/)
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(3) ARM/LM3S6918 (arch/arm/src/lm/)
(5) ARM/STM32 (arch/arm/src/stm32/)
(5) 8051 / MCS51 (arch/8051/)
(1) Hitachi/Renesas SH-1 (arch/sh/src/sh1)
(9) z16 (arch/z16/)
apps/
(5) Network Utilities (apps/netutils/)
(1) System libraries apps/system (apps/system)
(5) Other Applications & Tests (apps/examples/)
Title: CHILD PTHREAD TERMINATION
Description: When a tasks exits, shouldn't all of its child pthreads also be
terminated?
Status: Closed. No, this behavior will not be implemented.
Priority: Medium, required for good emulation of process/pthread model.
Title: TICKLESS OS
Description: On a side note, I have thought about a tick-less timer for the OS
for a long time. Basically we could replace the periodic system
timer interrupt with a one-shot interval timer programmed for the
next interesting event time. That is one way to both reduce the
timer interrupt overhead and also to increase the accuracy of
delays.
Current timer processing is in sched/sched_processtimer.c:
1) Calls clock_timer() which just increments a counter (the system
timer -- basically "up-time"). This is only used when code asks
for the current time. In a tickless OS, some substitute answer
for the question "What time is it?" would need to be developed.
You could use an RTC? Or maybe logic that gets the time until the
next interval expiration and computes the current time. The
solution is not too difficult, but depends on a hardware solution.
2) Calls wd_timer() which handles the link list of ordered events:
Each timer event is saved with the delta time to the next event
in the list. So an interval timer would be perfect to implement this.
3) sched_process_timeslice(). Then there is round-robin time-slicing.
The primary advantage of a tickless OS is that is would allow for
reduce power consumptions. That is because timer interrupts will
usually awaken CPUs from reduced power consumption states.
Status: Open. There will probably be no tickless OS implementation unless
someone gets motivated and drives the change.
Title: pause() NON-COMPLIANCE
Description: In the POSIX description of this function is the pause() function
will suspend the calling thread until delivery of a signal whose
action is either to execute a signal-catching function or to
terminate the process. The current implementation only waits for
any non-blocked signal to be received. It should only wake up if
the signal is delivered to a handler.
Status: Open.
Priority: Medium Low.
Title: ON-DEMAND PAGE INCOMPLETE
Description: On-demand paging has recently been incorporated into the RTOS.
The design of this feature is described here:
http://www.nuttx.org/NuttXDemandPaging.html.
As of this writing, the basic feature implementation is
complete and much of the logic has been verified. The test
harness for the feature exists only for the NXP LPC3131 (see
configs/ea3131/pgnsh and locked directories). There are
some limitations of this testing so I still cannot say that
the feature is fully functional.
Status: Open. This has been put on the shelf for some time.
Description: get_environ_ptr() (sched/sched_getenvironptr.c) is not implemented.
The representation of the the environment strings selected for
NutX is not compatible with the operation. Some significant
re-design would be required to implement this funcion and that
effort is thought to be not worth the result.
Description: timer_getoverrun() (sched/timer_getoverrun.c) is not implemented.
Status: Open
Priority: Low -- There is no plan to implement this.
Title: USER-SPACE WORK QUEUES
Description: There has been some use of work queues that has crept into some
user code. I am thinking of NxWidgets::CNxTimer. That timer
logic was originally implemented (correctly) using POSIX timers,
but was re-implemented using timed work.
The issue is that NxWidgets::CNxTimer is a user-space application
but the work queues are an OS internal feature. This will be a
problem for KERNEL builds. Hooks and definitions have been added
in include/nuttx/wqueue.h to support a user-space work queue, but
the corresponding logic has not been implemented.
The work queue logic will need to be moved from sched/ to libc/wqueue/
Status: Open. No work will probably be done until a functional KERNEL build
that includes NxWisges::CNxTimer is needed.
Priority: Medium Low for now
Title: INCOMPATIBILITES 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: RETAINING TASK EXIT STATUS
Description: When a task exists, its exit status should be retained in
so data structure until it is reaped (via waitpid(), or
similar interface) or until the parent thread exists.
You would think that this should be a clone of the existing
pthread join logic. Howver there is no need for zombies
in NuttX so no need to keep the status if the parent has
already exit'ed. Other simplifications:
1. Keep the array/list of return status in the parent
tasks TCB.
2. Use a fixed size array of return status (perhaps the
the enire array is allocated so that that is con
penalty for tasks that have no childre.
At present, exit status is not retained. If waitpid()
is called after the child task has exit'ed it simpley
returns with the ECHLD error. That is not too bad, but
does not tell you what the exit status was.
A work-around is to:
1) Call sched_lock() to disable pre-emption.
2) Start the task (it cannot run because pre-emption is
disbled.
3) Call waitpid();
4) Call sched_unlock() to re-enable pre-emption.
Status: Open
Priority: Low
Title: IMPROVED TASK CONTROL BLOCK STRUCTURE
All task resources that are shared amongst threads have
their own "break-away", reference-counted structure. The
Task Control Block (TCB) of each thread holds a reference
to each breakaway structure (see include/nuttx/sched.h).
It would be more efficent to have one reference counted
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