Quality RTOS & Embedded Software

 Real time embedded FreeRTOS RSS feed 
Quick Start Supported MCUs PDF Books Trace Tools Ecosystem TCP & FAT


Tickless idle atmel sam3x device

Posted by wlauer on November 20, 2014

I've been experimenting with the tickless idle functionality and have a few questions. I need to put our device into a lower power mode which involves changing the main clock speed to a lower value and restoring it upon waking. I've figured out all the details and it works as expected.

But I ran into an issue where the device would enter sleep mode while waiting on peripherals to complete. Unfortunately when entering sleep the resulting change in the main clock also changes affects the peripherals operation. So I modified the sleepmgr code that atmel provides to provide a locking mechanism around the code that deals with the peripherals.

As you can see I wrapped a mutex around a variable array that keeps the lock count for various depths of sleeping. So I though I would put the call sleepmgrgetsleepmode() to determine if we should sleep or not into the portSUPPRESSTICKSANDSLEEP call only to realize that portSUPPRESSTICKSAND_SLEEP is just another hook into the Idle task which can have no blocking calls.

How should I be handling this? How do i get around not blocking in the idle task?

Thanks in advance, Bill

a snippet of the sleepmgr code:

static inline void sleepmgrinit(void) { uint8t i;

/* semaphore used to access the sleep level as it is written to from more than one task. */
sleepmgr_mutex = xSemaphoreCreateMutex();
xSemaphoreTake(sleepmgr_mutex, portMAX_DELAY);

for (i = 0; i < SLEEPMGR_NR_OF_MODES - 1; i++) {
	sleepmgr_locks[i] = 0;
sleepmgr_locks[SLEEPMGR_NR_OF_MODES - 1] = 1;


static inline void sleepmgrlockmode(enum sleepmgrmode mode) { Assert(sleepmgrlocks[mode] < 0xff); xSemaphoreTake(sleepmgrmutex, portMAXDELAY); ++sleepmgrlocks[mode]; xSemaphoreGive(sleepmgrmutex); }

static inline enum sleepmgrmode sleepmgrgetsleepmode(void) { xSemaphoreTake(sleepmgrmutex, portMAXDELAY); enum sleepmgrmode sleepmode = SLEEPMGR_ACTIVE;

uint8_t *lock_ptr = sleepmgr_locks;
// Find first non-zero lock count, starting with the shallowest modes.
while (!(*lock_ptr)) {

// Catch the case where one too many sleepmgr_unlock_mode() call has been
// performed on the deepest sleep mode.
Assert((uintptr_t)(lock_ptr - sleepmgr_locks) < SLEEPMGR_NR_OF_MODES);

return sleep_mode;


Tickless idle atmel sam3x device

Posted by davedoors on November 21, 2014

The semaphore is probably only needed when changing the lock count. So tasks that update the lock count could use the functions with the mutex, and the idle task could use a function without a mutex just to read the lock counts as long is it does not change them. Would that work for you?

[ Back to the top ]    [ About FreeRTOS ]    [ Sitemap ]    [ ]

Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.

Latest News

FreeRTOS kernel V10 is available for immediate download. Now MIT licensed.

FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

IAR Partner

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers

STMicro RTOS partner supporting ARM7, ARM Cortex-M3, ARM Cortex-M4 and ARM Cortex-M0

Texas Instruments MCU Developer Network RTOS partner for ARM and MSP430 microcontrollers

OpenRTOS and SafeRTOS