This commit introduces a new MPU wrapper that places additional
restrictions on unprivileged tasks. The following is the list of changes
introduced with the new MPU wrapper:
1. Opaque and indirectly verifiable integers for kernel object handles:
All the kernel object handles (for example, queue handles) are now
opaque integers. Previously object handles were raw pointers.
2. Saving the task context in Task Control Block (TCB): When a task is
swapped out by the scheduler, the task's context is now saved in its
TCB. Previously the task's context was saved on its stack.
3. Execute system calls on a separate privileged only stack: FreeRTOS
system calls, which execute with elevated privilege, now use a
separate privileged only stack. Previously system calls used the
calling task's stack. The application writer can control the size of
the system call stack using new configSYSTEM_CALL_STACK_SIZE config
macro.
4. Memory bounds checks: FreeRTOS system calls which accept a pointer
and de-reference it, now verify that the calling task has required
permissions to access the memory location referenced by the pointer.
5. System call restrictions: The following system calls are no longer
available to unprivileged tasks:
- vQueueDelete
- xQueueCreateMutex
- xQueueCreateMutexStatic
- xQueueCreateCountingSemaphore
- xQueueCreateCountingSemaphoreStatic
- xQueueGenericCreate
- xQueueGenericCreateStatic
- xQueueCreateSet
- xQueueRemoveFromSet
- xQueueGenericReset
- xTaskCreate
- xTaskCreateStatic
- vTaskDelete
- vTaskPrioritySet
- vTaskSuspendAll
- xTaskResumeAll
- xTaskGetHandle
- xTaskCallApplicationTaskHook
- vTaskList
- vTaskGetRunTimeStats
- xTaskCatchUpTicks
- xEventGroupCreate
- xEventGroupCreateStatic
- vEventGroupDelete
- xStreamBufferGenericCreate
- xStreamBufferGenericCreateStatic
- vStreamBufferDelete
- xStreamBufferReset
Also, an unprivileged task can no longer use vTaskSuspend to suspend
any task other than itself.
We thank the following people for their inputs in these enhancements:
- David Reiss of Meta Platforms, Inc.
- Lan Luo, Xinhui Shao, Yumeng Wei, Zixia Liu, Huaiyu Yan and Zhen Ling
of School of Computer Science and Engineering, Southeast University,
China.
- Xinwen Fu of Department of Computer Science, University of
Massachusetts Lowell, USA.
- Yuequi Chen, Zicheng Wang, Minghao Lin of University of Colorado
Boulder, USA.
Patrick Cook [Mon, 10 Jul 2023 22:08:59 +0000 (15:08 -0700)]
Fix circular dependency in CMake project (#700)
* Fix circular dependency in cmake project
Fix for https://github.com/FreeRTOS/FreeRTOS-Kernel/issues/687
In order for custom ports to also break the cycle, they must link
against freertos_kernel_include instead of freertos_kernel.
Signed-off-by: Devaraj Ranganna <devaraj.ranganna@arm.com>
* Armv8-M: Add support for interrupt priority check
FreeRTOS provides `FromISR` system calls which can be called directly
from interrupt service routines. It is crucial that the priority of
these ISRs is set to same or lower value (numerically higher) than that
of `configMAX_SYSCALL_INTERRUPT_PRIORITY`. For more information refer
to https://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html.
Add a check to trigger an assert when an ISR with priority higher
(numerically lower) than `configMAX_SYSCALL_INTERRUPT_PRIORITY` calls
`FromISR` system calls if `configASSERT` macro is defined.
In addition, add a config option
`configQEMU_DISABLE_INTERRUPT_PRIO_BITS_CHECK` to disable interrupt
priority check while running on QEMU. Based on the discussion
https://gitlab.com/qemu-project/qemu/-/issues/1122, The interrupt
priority bits in QEMU do not match the real hardware. Therefore the
assert that checks the number of implemented bits and __NVIC_PRIO_BITS
will always fail. The config option
`configQEMU_DISABLE_INTERRUPT_PRIO_BITS_CHECK` should be defined in the
`FreeRTOSConfig.h` for QEMU targets.
Signed-off-by: Devaraj Ranganna <devaraj.ranganna@arm.com>
* Use SHPR2 for calculating interrupt priority bits
This removes the dependency on the secure software to mark the interrupt
as non-secure.
Paul Bartell [Thu, 20 Apr 2023 05:24:54 +0000 (22:24 -0700)]
ARMv7M: Adjust implemented priority bit assertions (#665)
Adjust assertions related to the CMSIS __NVIC_PRIO_BITS and FreeRTOS
configPRIO_BITS configuration macros such that these macros specify the
minimum number of implemented priority bits supported by a config
build rather than the exact number of implemented priority bits.
Vo Trung Chi [Tue, 4 Apr 2023 15:10:54 +0000 (22:10 +0700)]
fix conversion warning (#658)
FreeRTOS-Kernel/portable/GCC/ARM_CM4F/port.c:399:41: error: conversion from 'uint32_t' {aka 'long unsigned int'} to 'uint8_t' {aka 'unsigned char'} may change value [-Werror=conversion]
Signed-off-by: Vo Trung Chi <chi.votrung@vn.bosch.com>
Gaurav-Aggarwal-AWS [Tue, 28 Mar 2023 11:31:37 +0000 (17:01 +0530)]
Only add alignment padding when needed (#650)
Heap 4 and Heap 5 add some padding to ensure that the allocated blocks
are always aligned to portBYTE_ALIGNMENT bytes. The code until now was
adding padding always even if the resulting block was already aligned.
This commits updates the code to only add padding if the resulting block
is not aligned.
Darian [Wed, 22 Mar 2023 22:27:57 +0000 (06:27 +0800)]
Add functions to get the buffers of statically created objects (#641)
Added various ...GetStaticBuffer() functions to get the buffers of statically
created objects.
--------- Co-authored-by: Paul Bartell <pbartell@amazon.com> Co-authored-by: Nikhil Kamath <110539926+amazonKamath@users.noreply.github.com> Co-authored-by: Gaurav Aggarwal <aggarg@amazon.com>
Gaurav-Aggarwal-AWS [Fri, 17 Mar 2023 02:52:34 +0000 (08:22 +0530)]
Run kernel demos and unit tests for PR changes (#645)
* Run kernel demos and unit tests for PR changes
Kernel demos check builds multiple demos from FreeRTOS/FreeRTOS and
unit tests check runs unit tests in FreeRTOS/FreeRTOS. Both of these
checks currently use main branch of FreeRTOS-Kernel. This commits
updates these checks to use the changes in the PR.
Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>
* Do not specify PR SHA explicitly as that is default
Kody Stribrny [Tue, 7 Mar 2023 04:04:15 +0000 (20:04 -0800)]
Fix freertos_kernel cmake property, Posix Port (#640)
* Fix freertos_kernel cmake property, Posix Port
* Moves the `set_property()` call below the target definition in top level CMakeLists file
* Corrects billion value from `ULL` suffix (not C90 compliant) to `UL` suffix with cast to uint64_t
Paul Bartell [Mon, 6 Mar 2023 16:19:28 +0000 (08:19 -0800)]
Enable building the GCC Cortex-R5 port without an FPU (#586)
* Ensure configUSE_TASK_FPU_SUPPORT option is set correctly
If one does enable the FPU of the Cortex-R5 processor, then the GCC
compiler will define the macro __ARM_FP. This can be used to ensure,
that the configUSE_TASK_FPU_SUPPORT is set accordingly.
* Enable the implementation of vPortTaskUsesFPU only if configUSE_TASK_FPU_SUPPORT is set to 1
* Remove error case in pxPortInitialiseStack
The case of configUSE_TASK_FPU_SUPPORT is 0 is now handled
* Enable access to FPU registers only if FPU is enabled
Keith Packard [Mon, 6 Mar 2023 06:29:39 +0000 (22:29 -0800)]
Fix TLS and stack alignment when using picolibc (#637)
Both the TLS block and stack must be correctly aligned when using
picolibc. The architecture stack alignment is represented by the
portBYTE_ALIGNMENT_MASK and the TLS block alignment is provided by the
Picolibc _tls_align() inline function for Picolibc version 1.8 and
above. For older versions of Picolibc, we'll assume that the TLS block
requires the same alignment as the stack.
For downward growing stacks, this requires aligning the start of the
TLS block to the maximum of the stack alignment and the TLS
alignment. With this, both the TLS block and stack will now be
correctly aligned.
For upward growing stacks, the two areas must be aligned
independently; the TLS block is aligned from the start of the stack,
then the tls space is allocated, and then the stack is aligned above
that.
It's probably useful to know here that the linker ensures that
variables within the TLS block are assigned offsets that match their
alignment requirements. If the TLS block itself is correctly aligned,
then everything within will also be.
I have only tested the downward growing stack branch of this patch.
Signed-off-by: Keith Packard <keithpac@amazon.com> Co-authored-by: Keith Packard <keithpac@amazon.com> Co-authored-by: Gaurav-Aggarwal-AWS <33462878+aggarg@users.noreply.github.com>
Chris Copeland [Thu, 2 Mar 2023 17:49:56 +0000 (09:49 -0800)]
Interrupt priority assert improvements for CM3/4/7 (#602)
* Interrupt priority assert improvements for CM3/4/7
In the ARM_CM3, ARM_CM4, and ARM_CM7 ports, change the assertion that
`configMAX_SYSCALL_INTERRUPT_PRIORITY` is nonzero to account for the
number of priority bits implemented by the hardware.
Change these ports to also use the lowest priority for PendSV and
SysTick, ignoring `configKERNEL_INTERRUPT_PRIORITY`.
* Remove not needed configKERNEL_INTERRUPT_PRIORITY define
Keith Packard [Thu, 2 Mar 2023 16:26:04 +0000 (08:26 -0800)]
Add Thread Local Storage (TLS) support using Picolibc functions (#343)
* Pass top of stack to configINIT_TLS_BLOCK
Picolibc wants to allocate the per-task TLS block within the stack
segment, so it will need to modify the top of stack value. Pass the
pxTopOfStack variable to make this explicit.
Signed-off-by: Keith Packard <keithpac@amazon.com>
* Move newlib-specific definitions to separate file
This reduces the clutter in FreeRTOS.h caused by having newlib-specific
macros present there.
Signed-off-by: Keith Packard <keithpac@amazon.com>
* Make TLS code depend only on configUSE_C_RUNTIME_TLS_SUPPORT
Remove reference to configUSE_NEWLIB_REENTRANT as that only works
when using newlib. configUSE_C_RUNTIME_TLS_SUPPORT is always
set when configUSE_NEWLIB_REENTRANT is set, so using both was
redundant in that case.
Signed-off-by: Keith Packard <keithpac@amazon.com>
* portable-ARC: Adapt ARC support to use generalized TLS support
With generalized thread local storage (TLS) support present in the
core, the two ARC ports need to have the changes to the TCB mirrored
to them.
Signed-off-by: Keith Packard <keithpac@amazon.com>
* Add Thread Local Storage (TLS) support using Picolibc functions
This patch provides definitions of the general TLS support macros in
terms of the Picolibc TLS support functions.
Picolibc is normally configured to use TLS internally for all
variables that are intended to be task-local, so these changes are
necessary for picolibc to work correctly with FreeRTOS.
The picolibc helper functions rely on elements within the linker
script to arrange the TLS data in memory and define some symbols.
Applications wanting to use this mechanism will need changes in their
linker script when migrating to picolibc.
Signed-off-by: Keith Packard <keithpac@amazon.com>
---------
Signed-off-by: Keith Packard <keithpac@amazon.com> Co-authored-by: Keith Packard <keithpac@amazon.com> Co-authored-by: Gaurav-Aggarwal-AWS <33462878+aggarg@users.noreply.github.com>
Gaurav-Aggarwal-AWS [Thu, 23 Feb 2023 04:07:42 +0000 (09:37 +0530)]
Fix build failure introduced in PR #597 (#629)
The PR #597 introduced a new config option configTICK_TYPE_WIDTH_IN_BITS
which can be defined to one of the following:
* TICK_TYPE_WIDTH_16_BITS - Tick type is 16 bit wide.
* TICK_TYPE_WIDTH_32_BITS - Tick type is 32 bit wide.
* TICK_TYPE_WIDTH_64_BITS - Tick type is 64 bit wide.
Earlier we supported 16 and 32 bit width for tick type which was
controlled using the config option configUSE_16_BIT_TICKS. The PR
tried to maintain backward compatibility by honoring
configUSE_16_BIT_TICKS. The backward compatibility did not work as
expected though, as the macro configTICK_TYPE_WIDTH_IN_BITS was used
before it was defined. This PR addresses it by ensuring that the macro
configTICK_TYPE_WIDTH_IN_BITS is defined before it is used.
Testing
1. configUSE_16_BIT_TICKS is defined to 0.
It is clear from assembly that the tick type is 32 bit.
5. configTICK_TYPE_WIDTH_IN_BITS is defined to TICK_TYPE_WIDTH_64_BITS.
```
#error configTICK_TYPE_WIDTH_IN_BITS set to unsupported tick type width.
```
The testing was done for GCC/ARM_CM3 port which does not support 64 bit
tick type.
6. Neither configUSE_16_BIT_TICKS nor configTICK_TYPE_WIDTH_IN_BITS
defined.
```
#error Missing definition: One of configUSE_16_BIT_TICKS and
configTICK_TYPE_WIDTH_IN_BITS must be defined in FreeRTOSConfig.h.
See the Configuration section of the FreeRTOS API documentation for
details.
```
7. Both configUSE_16_BIT_TICKS and configTICK_TYPE_WIDTH_IN_BITS defined.
```
#error Only one of configUSE_16_BIT_TICKS and
configTICK_TYPE_WIDTH_IN_BITS must be defined in FreeRTOSConfig.h.
See the Configuration section of the FreeRTOS API documentation for
details.
```
Related issue - https://github.com/FreeRTOS/FreeRTOS-Kernel/issues/628
bbain [Mon, 13 Feb 2023 04:58:20 +0000 (15:58 +1100)]
Introduce portMEMORY_BARRIER for Microblaze port. (#621)
The introduction of `portMEMORY_BARRIER` will ensure
the places in the kernel use a barrier will work.
For example, `xTaskResumeAll` has a memory barrier
to ensure its correctness when compiled with optimization
enabled. Without the barrier `xTaskResumeAll` can fail
(e.g. start reading and writing to address 0 and/or
infinite looping) when `xPendingReadyList` contains more
than one task to restore.
In `xTaskResumeAll` the compiler chooses to cache the
`pxTCB` the first time through the loop for use
in every subsequent loop. This is incorrect as the
removal of `pxTCB->xEventListItem` will actually
change the value of `pxTCB` if it was read again
at the top of the loop. The barrier forces the compiler
to read `pxTCB` again at the top of the loop.
The compiler is operating correctly. The removal
`pxTCB->xEventListItem` executes on a `List_t *`
and `ListItem_t *`. This means that the compiler
can assume that any `MiniListItem_t` values are
unchanged by the loop (i.e. "strict-aliasing").
This allows the compiler to cache `pxTCB` as it
is obtained via a `MiniListItem_t`. This is incorrect
in this case because it is possible for a `ListItem_t *`
to actually alias a `MiniListItem_t`. This is technically
a "violation of aliasing rules" so we use the the barrier
to disable the strict-aliasing optimization in this loop.
Chris Copeland [Thu, 19 Jan 2023 22:46:42 +0000 (14:46 -0800)]
Add ulTaskGetRunTimeCounter and ulTaskGetRunTimePercent (#611)
Allow ulTaskGetIdleRunTimeCounter and ulTaskGetIdleRunTimePercent to be
used whenever configGENERATE_RUN_TIME_STATS is enabled, as this is the
only requirement for these functions to work.
Archit Gupta [Thu, 15 Dec 2022 21:46:32 +0000 (21:46 +0000)]
Fix array-bounds compiler warning on gcc11+ in list.h (#580)
listGET_OWNER_OF_NEXT_ENTRY computes `( pxConstList )->pxIndex->pxNext` after
verifying that `( pxConstList )->pxIndex` points to `xListEnd`, which due to
being a MiniListItem_t, can be shorter than a ListItem_t. Thus,
`( pxConstList )->pxIndex` is a `ListItem_t *` that extends past the end of the
`List_t` whose `xListEnd` it points to. This is fixed by accessing `pxNext`
through a `MiniListItem_t` instead.
ChristosZosi [Mon, 14 Nov 2022 05:18:47 +0000 (06:18 +0100)]
Add support for the configUSE_TASK_FPU_SUPPORT constant in the GCC/ARM_CR5 port (#584)
* Add support for the configUSE_TASK_FPU_SUPPORT in the GCC/ARM_CR5 port
This is done almost identically as in the GCC/ARM_CA9 port
* Adjust task stack initialitation of the GCC/ARM_CR5 port
Ensure that the task stack initialization is done correctly for the
different options of configUSE_TASK_FPU_SUPPORT.
This is very similar to the GCC/ARM_CA9 port. The only meaningful
difference is, that the FPU of the Cortex-R5 has just sixteen 64-bit
floating point registers as it implements the VFPv3-D16 architecture.
You may also refer to the ARM documentation
* Add support for FPU safe interrupts to the GCC/ARM_CR5 port
Similar to GCC/ARM_CA9 port
* Clarify comment about the size of the FPU registers of Cortex R5
Gaurav-Aggarwal-AWS [Tue, 8 Nov 2022 08:35:35 +0000 (14:05 +0530)]
Fix context switch when time slicing is off (#568)
* Fix context switch when time slicing is off
When time slicing is off, context switch should only happen when a
task with priority higher than the currently executing one is unblocked.
Earlier the code was invoking a context switch even when a task with
priority equal the currently executing task was unblocked. This commit
fixes the code to only do a context switch when a higher priority
task is unblocked.
Niklas Gürtler [Thu, 13 Oct 2022 17:22:24 +0000 (19:22 +0200)]
Removed the 'configASSERT( xInheritanceOccurred == pdFALSE )' assertion from xQueueSemaphoreTake as the reasoning behind it is wrong; it can trigger on wrongly on highly-contested semaphores on multicore systems. See https://forums.freertos.org/t/15967 (#576)
Jeff Tenney [Mon, 3 Oct 2022 19:39:17 +0000 (12:39 -0700)]
Tickless idle fixes/improvement (#59)
* Fix tickless idle when stopping systick on zero...
...and don't stop SysTick at all in the eAbortSleep case.
Prior to this commit, if vPortSuppressTicksAndSleep() happens to stop
the SysTick on zero, then after tickless idle ends, xTickCount advances
one full tick more than the time that actually elapsed as measured by
the SysTick. See "bug 1" in this forum post:
https://forums.freertos.org/t/ultasknotifytake-timeout-accuracy/9629/40
SysTick
-------
The SysTick is the hardware timer that provides the OS tick interrupt
in the official ports for Cortex M. SysTick starts counting down from
the value stored in its reload register. When SysTick reaches zero, it
requests an interrupt. On the next SysTick clock cycle, it loads the
counter again from the reload register. To get periodic interrupts
every N SysTick clock cycles, the reload register must be N - 1.
Bug Example
-----------
- Idle task calls vPortSuppressTicksAndSleep(xExpectedIdleTime = 2).
[Doesn't have to be "2" -- could be any number.]
- vPortSuppressTicksAndSleep() stops SysTick, and the current-count
register happens to stop on zero.
- SysTick ISR executes, setting xPendedTicks = 1
- vPortSuppressTicksAndSleep() masks interrupts and calls
eTaskConfirmSleepModeStatus() which confirms the sleep operation. ***
- vPortSuppressTicksAndSleep() configures SysTick for 1 full tick
(xExpectedIdleTime - 1) plus the current-count register (which is 0)
- One tick period elapses in sleep.
- SysTick wakes CPU, ISR executes and increments xPendedTicks to 2.
- vPortSuppressTicksAndSleep() calls vTaskStepTick(1), then returns.
- Idle task resumes scheduler, which increments xTickCount twice (for
xPendedTicks = 2)
In the end, two ticks elapsed as measured by SysTick, but the code
increments xTickCount three times. The root cause is that the code
assumes the SysTick current-count register always contains the number of
SysTick counts remaining in the current tick period. However, when the
current-count register is zero, there are ulTimerCountsForOneTick
counts remaining, not zero. This error is not the kind of time slippage
normally associated with tickless idle.
*** Note that a recent commit https://github.com/FreeRTOS/FreeRTOS-Kernel/commit/e1b98f0
results in eAbortSleep in this case, due to xPendedTicks != 0. That
commit does mostly resolve this bug without specifically mentioning
it, and without this commit. But that resolution allows the code in
port.c not to directly address the special case of stopping SysTick on
zero in any code or comments. That commit also generates additional
instances of eAbortSleep, and a second purpose of this commit is to
optimize how vPortSuppressTicksAndSleep() behaves for eAbortSleep, as
noted below.
This commit also includes an optimization to avoid stopping the SysTick
when eTaskConfirmSleepModeStatus() returns eAbortSleep. This
optimization belongs with this fix because the method of handling the
SysTick being stopped on zero changes with this optimization.
* Fix imminent tick rescheduled after tickless idle
Prior to this commit, if something other than systick wakes the CPU from
tickless idle, vPortSuppressTicksAndSleep() might cause xTickCount to
increment once too many times. See "bug 2" in this forum post:
https://forums.freertos.org/t/ultasknotifytake-timeout-accuracy/9629/40
SysTick
-------
The SysTick is the hardware timer that provides the OS tick interrupt
in the official ports for Cortex M. SysTick starts counting down from
the value stored in its reload register. When SysTick reaches zero, it
requests an interrupt. On the next SysTick clock cycle, it loads the
counter again from the reload register. To get periodic interrupts
every N SysTick clock cycles, the reload register must be N - 1.
Bug Example
-----------
- CPU is sleeping in vPortSuppressTicksAndSleep()
- Something other than the SysTick wakes the CPU.
- vPortSuppressTicksAndSleep() calculates the number of SysTick counts
until the next tick. The bug occurs only if this number is small.
- vPortSuppressTicksAndSleep() puts this small number into the SysTick
reload register, and starts SysTick.
- vPortSuppressTicksAndSleep() calls vTaskStepTick()
- While vTaskStepTick() executes, the SysTick expires. The ISR pends
because interrupts are masked, and SysTick starts a 2nd period still
based on the small number of counts in its reload register. This 2nd
period is undesirable and is likely to cause the error noted below.
- vPortSuppressTicksAndSleep() puts the normal tick duration into the
SysTick's reload register.
- vPortSuppressTicksAndSleep() unmasks interrupts before the SysTick
starts a new period based on the new value in the reload register.
[This is a race condition that can go either way, but for the bug
to occur, the race must play out this way.]
- The pending SysTick ISR executes and increments xPendedTicks.
- The SysTick expires again, finishing the second very small period, and
starts a new period this time based on the full tick duration.
- The SysTick ISR increments xPendedTicks (or xTickCount) even though
only a tiny fraction of a tick period has elapsed since the previous
tick.
The bug occurs when *two* consecutive small periods of the SysTick are
both counted as ticks. The root cause is a race caused by the small
SysTick period. If vPortSuppressTicksAndSleep() unmasks interrupts
*after* the small period expires but *before* the SysTick starts a
period based on the full tick period, then two small periods are
counted as ticks when only one should be counted.
The end result is xTickCount advancing nearly one full tick more than
time actually elapsed as measured by the SysTick. This is not the kind
of time slippage normally associated with tickless idle.
After this commit the code starts the SysTick and then immediately
modifies the reload register to ensure the very short cycle (if any) is
conducted only once. This strategy requires special consideration for
the build option that configures SysTick to use a divided clock. To
avoid waiting around for the SysTick to load value from the reload
register, the new code temporarily configures the SysTick to use the
undivided clock. The resulting timing error is typical for tickless
idle. The error (commonly known as drift or slippage in kernel time)
caused by this strategy is equivalent to one or two counts in
ulStoppedTimerCompensation.
This commit also updates comments and #define symbols related to the
SysTick clock option. The SysTick can optionally be clocked by a
divided version of the CPU clock (commonly divide-by-8). The new code
in this commit adjusts these comments and symbols to make them clearer
and more useful in configurations that use the divided clock. The fix
made in this commit requires the use of these symbols, as noted in the
code comments.
* Fix tickless idle with alternate systick clocking
Prior to this commit, in configurations using the alternate SysTick
clocking, vPortSuppressTicksAndSleep() might cause xTickCount to jump
ahead as much as the entire expected idle time or fall behind as much
as one full tick compared to time as measured by the SysTick.
SysTick
-------
The SysTick is the hardware timer that provides the OS tick interrupt
in the official ports for Cortex M. SysTick starts counting down from
the value stored in its reload register. When SysTick reaches zero, it
requests an interrupt. On the next SysTick clock cycle, it loads the
counter again from the reload register. The SysTick has a configuration
option to be clocked by an alternate clock besides the core clock.
This alternate clock is MCU dependent.
Scenarios Fixed
---------------
The new code in this commit handles the following scenarios that were
not handled correctly prior to this commit.
1. Before the sleep, vPortSuppressTicksAndSleep() stops the SysTick on
zero, long after SysTick reached zero. Prior to this commit, this
scenario caused xTickCount to jump ahead one full tick for the same
reason documented here: https://github.com/FreeRTOS/FreeRTOS-Kernel/pull/59/commits/0c7b04bd3a745c52151abebc882eed3f811c4c81
2. After the sleep, vPortSuppressTicksAndSleep() stops the SysTick
before it loads the counter from the reload register. Prior to this
commit, this scenario caused xTickCount to jump ahead by the entire
expected idle time (xExpectedIdleTime) because the current-count
register is zero before it loads from the reload register.
3. Prior to return, vPortSuppressTicksAndSleep() attempts to start a
short SysTick period when the current SysTick clock cycle has a lot of
time remaining. Prior to this commit, this scenario could cause
xTickCount to fall behind by as much as nearly one full tick because the
short SysTick cycle never started.
Note that #3 is partially fixed by https://github.com/FreeRTOS/FreeRTOS-Kernel/pull/59/commits/967acc9b200d3d4beeb289d9da9e88798074b431
even though that commit addresses a different issue. So this commit
completes the partial fix.
* Improve comments and name of preprocessor symbol
Add a note in the code comments that SysTick requests an interrupt when
decrementing from 1 to 0, so that's why stopping SysTick on zero is a
special case. Readers might unknowingly assume that SysTick requests
an interrupt when wrapping from 0 back to the load-register value.
Reconsider new "_SETTING" suffix since "_CONFIG" suffix seems more
descriptive. The code relies on *both* of these preprocessor symbols:
A meaningful suffix is really helpful to distinguish the two symbols.
* Revert introduction of 2nd name for NVIC register
When I added portNVIC_ICSR_REG I didn't realize there was already a
portNVIC_INT_CTRL_REG, which identifies the same register. Not good
to have both. Note that portNVIC_INT_CTRL_REG is defined in portmacro.h
and is already used in this file (port.c).
* Replicate to other Cortex M ports
Also set a new fiddle factor based on tests with a CM4F. I used gcc,
optimizing at -O1. Users can fine-tune as needed.
Also add configSYSTICK_CLOCK_HZ to the CM0 ports to be just like the
other Cortex M ports. This change allowed uniformity in the default
tickless implementations across all Cortex M ports. And CM0 is likely
to benefit from configSYSTICK_CLOCK_HZ, especially considering new CM0
devices with very fast CPU clock speeds.
* Revert changes to IAR-CM0-portmacro.h
portNVIC_INT_CTRL_REG was already defined in port.c. No need to define
it in portmacro.h.
* Handle edge cases with slow SysTick clock
Co-authored-by: Cobus van Eeden <35851496+cobusve@users.noreply.github.com> Co-authored-by: abhidixi11 <44424462+abhidixi11@users.noreply.github.com> Co-authored-by: Joseph Julicher <jjulicher@mac.com> Co-authored-by: alfred gedeon <28123637+alfred2g@users.noreply.github.com>
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