Fix support for stepping tick by xExpectedIdleTime (#73)

* Fix support for stepping maximum number of ticks

This commit fixes support for tickless implementations that call
vTaskStepTick() with the maximum number of allowed ticks to step.

Function vTaskStepTick() provides a way for the tickless idle
implementation to account for ticks that elapse during tickless idle.
The maximum number of stepped ticks allowed is the number passed to
portSUPPRESS_TICKS_AND_SLEEP().  It is the number of ticks between
xTickCount and xNextTaskUnblockTime.

vTaskStepTick() is specifically intended for use with tickless idle,
so it always executes with the scheduler disabled.  For reference,
compare it with the more general function xTaskCatchUpTicks().

Without this Change
Prior to this commit, if a task is supposed to wake at xTickCount ==
0xFFFFFFFF, then when tickless idle ends, function vTaskStepTick()
sets the tick to 0xFFFFFFFF but the task remains on the delayed list
because xTaskIncrementTick() does not execute.  One tick later,
xTaskIncrementTick() executes because it's time to increment xTickCount
to 0x00000000.  An assertion failure occurs in
taskSWITCH_DELAYED_LISTS() because the delayed task list is not
empty.  Other examples of valling vTaskStepTick() with the maximum
allowed number of ticks merely result in a task waking one tick late.

Default Tickless Implementations
Note that the default tickless implementations never pass the maximum
allowed value to vTaskStepTick().  The default implementations use the
tick interrupt to finish the sleep and allow that one tick to be
counted normally via the tick ISR and xTaskIncrementTick().

* Protect xPendedTicks with critical section

Function xTaskIncrementTick() increments xPendedTicks when the
scheduler is disabled.  That function typically executes inside the tick
ISR.  So code in xTaskCatchUpTicks() must mask interrupts when modifying

* uncrustify tasks.c

* Update tasks.c

Style changes only - added comment and indentation to the two modified files.

* uncrustify

* Add test coverage for new conditional

* Add typecast

Co-authored-by: Cobus van Eeden <>
Co-authored-by: Joseph Julicher <>
Co-authored-by: RichardBarry <>
2 files changed
tree: b835696236c143ad40d4d891fd66a0b3f72c0a6a
  1. .github/
  2. include/
  3. portable/
  4. .gitmodules
  5. croutine.c
  6. event_groups.c
  7. GitHub-FreeRTOS-Kernel-Home.url
  8. History.txt
  10. list.c
  11. queue.c
  12. Quick_Start_Guide.url
  14. stream_buffer.c
  15. tasks.c
  16. timers.c

Getting started

This repository contains FreeRTOS kernel source/header files and kernel ports only. This repository is referenced as a submodule in FreeRTOS/FreeRTOS repository, which contains pre-configured demo application projects under FreeRTOS/Demo directory.

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  • The root of this repository contains the three files that are common to every port - list.c, queue.c and tasks.c. The kernel is contained within these three files. croutine.c implements the optional co-routine functionality - which is normally only used on very memory limited systems.

  • The ./portable directory contains the files that are specific to a particular microcontroller and/or compiler. See the readme file in the ./portable directory for more information.

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lexicon.txt contains words that are not traditionally found in an English dictionary. It is used by the spellchecker to verify the various jargon, variable names, and other odd words used in the FreeRTOS code base. If your pull request fails to pass the spelling and you believe this is a mistake, then add the word to lexicon.txt. Note that only the FreeRTOS Kernel source files are checked for proper spelling, the portable section is ignored.