FreeRTOS example for small memory footprint

I am working on a small project with an STM32F038 MCU. This device has only 4K of SRAM and I have been struggling to get FreeRTOS configured so the project builds and at least runs a single test task.

In spite of searching I have been unable to find an example configuration for FreeRTOS to operate in this small amount of SRAM.

My project will require just three, maybe four, tasks.

I would much appreciate a pointer to an example configuration to guide my project.

I think the key to running in limited memory conditions is that you need to be careful how you use the memory and you can’t just give more than enough to be safe.

FreeRTOS naturally takes a fairly limited amount of memory for most of the primitives. I would likely just turn off dynamic allocations and allocate everything statically. This also means you don’t need to create a heap. You will also need to look carefully at stack sizes and not allocate too much stack for a task.

Start with only two task priority levels, so idle is below your task. Maybe in your final system you will go up to 3.

One big advantage of making everything static is that you can then look at the memory map and see what is taking up the memory, and look at the bigger things to see what can be put on a diet.

@richard-damon Thank you for the reply.

I have reduced all the memory configuration, I think, the project now compiles and links. However, when I run the project I get a hard fault exception. The task I have is very simple:

void tasktest(void * param)
{
	while(1)
	{
		vTaskDelay(pdMS_TO_TICKS(1000)) ;
		//HAL_Delay(500) ;
	}

}

I set a breakpoint on the delay line and start the code. I have tried tracing through the delay call and it appears the exception happens when the context switch is done, with the registers looking like a memory/stack corruption has occurred. If, as a simple test, I use the HAL_Delay call the task runs, but of course does not suspend.

This is my FreeRTOS config:

/*
 * FreeRTOS V202012.00
 * Copyright (C) 2020 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * http://www.FreeRTOS.org
 * http://aws.amazon.com/freertos
 *
 * 1 tab == 4 spaces!
 */

#ifndef FREERTOS_CONFIG_H
#define FREERTOS_CONFIG_H

/*-----------------------------------------------------------
 * Application specific definitions.
 *
 * These definitions should be adjusted for your particular hardware and
 * application requirements.
 *
 * THESE PARAMETERS ARE DESCRIBED WITHIN THE 'CONFIGURATION' SECTION OF THE
 * FreeRTOS API DOCUMENTATION AVAILABLE ON THE FreeRTOS.org WEB SITE.
 *
 * See http://www.freertos.org/a00110.html.
 *----------------------------------------------------------*/

/* Ensure definitions are only used by the compiler, and not by the assembler. */
#if defined(__ICCARM__) || defined(__CC_ARM) || defined(__GNUC__)
  #include <stdint.h>
  extern uint32_t SystemCoreClock;
#endif

#define configUSE_PREEMPTION					1
#define configSUPPORT_STATIC_ALLOCATION			0
#define configSUPPORT_DYNAMIC_ALLOCATION		1
#define configUSE_IDLE_HOOK						0
#define configUSE_TICK_HOOK						0
#define configCPU_CLOCK_HZ						( SystemCoreClock )
#define configTICK_RATE_HZ						( ( TickType_t ) 1000 )
#define configMAX_PRIORITIES					( 2 )
#define configMINIMAL_STACK_SIZE				( ( uint16_t ) 200 )
#define configTOTAL_HEAP_SIZE					( ( size_t ) 2500 )
#define configMAX_TASK_NAME_LEN					( 8 )
#define configUSE_TRACE_FACILITY				0
#define configUSE_16_BIT_TICKS					0
#define configUSE_MUTEXES						1
#define configQUEUE_REGISTRY_SIZE				8
#define configUSE_RECURSIVE_MUTEXES				0
#define configUSE_COUNTING_SEMAPHORES			0
#define configUSE_PORT_OPTIMISED_TASK_SELECTION	0
#define configUSE_MALLOC_FAILED_HOOK			0
#define configCHECK_FOR_STACK_OVERFLOW			0

/* Defaults to size_t for backward compatibility, but can be changed
 * if lengths will always be less than the number of bytes in a size_t. */
#define configMESSAGE_BUFFER_LENGTH_TYPE		size_t
/* USER CODE END MESSAGE_BUFFER_LENGTH_TYPE */

/* Software timer definitions. */
#define configUSE_TIMERS						0
#define configTIMER_TASK_PRIORITY				( 2 )
#define configTIMER_QUEUE_LENGTH				4
#define configTIMER_TASK_STACK_DEPTH			configMINIMAL_STACK_SIZE

/* Set the following definitions to 1 to include the API function, or zero
 * to exclude the API function. */
#define INCLUDE_vTaskPrioritySet				0
#define INCLUDE_uxTaskPriorityGet				0
#define INCLUDE_vTaskDelete						0
#define INCLUDE_vTaskCleanUpResources			0
#define INCLUDE_vTaskSuspend					0
#define INCLUDE_vTaskDelayUntil					0
#define INCLUDE_vTaskDelay						1
#define INCLUDE_xTaskGetSchedulerState			0
#define INCLUDE_xTimerPendFunctionCall			0
#define INCLUDE_xQueueGetMutexHolder			0
#define INCLUDE_uxTaskGetStackHighWaterMark		1
#define INCLUDE_eTaskGetState					1

  /* SystemView Specific */

#define	INCLUDE_xTaskGetIdleTaskHandle          1
#define	INCLUDE_pxTaskGetStackStart             1

/* Cortex-M specific definitions. */
#ifdef __NVIC_PRIO_BITS
	/* __BVIC_PRIO_BITS will be specified when CMSIS is being used. */
	#define configPRIO_BITS						__NVIC_PRIO_BITS
#else
	#define configPRIO_BITS						4
#endif

/* The lowest interrupt priority that can be used in a call to a "set priority"
 * function. */
#define configLIBRARY_LOWEST_INTERRUPT_PRIORITY	15

/* The highest interrupt priority that can be used by any interrupt service
 * routine that makes calls to interrupt safe FreeRTOS API functions.  DO NOT
 * CALL INTERRUPT SAFE FREERTOS API FUNCTIONS FROM ANY INTERRUPT THAT HAS A
 * HIGHER PRIORITY THAN THIS! (higher priorities are lower numeric values. */
#define configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY 5

/* Interrupt priorities used by the kernel port layer itself.  These are generic
 * to all Cortex-M ports, and do not rely on any particular library functions. */
#define configKERNEL_INTERRUPT_PRIORITY				( configLIBRARY_LOWEST_INTERRUPT_PRIORITY << ( 8 - configPRIO_BITS ) )
/* !!!! configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to zero !!!!
See http://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html. */
#define configMAX_SYSCALL_INTERRUPT_PRIORITY		( configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY << ( 8 - configPRIO_BITS ) )

/* Normal assert() semantics without relying on the provision of an assert.h
 * header file. */
#define configASSERT( x )							if ( ( x ) == 0 ) { taskDISABLE_INTERRUPTS(); for( ;; ); }

/* Definitions that map the FreeRTOS port interrupt handlers to their CMSIS
 * standard names. */

/*
 * These remapping defines are removed and the FreeRTOS handlers are added to the CMSIS handlers in stm320xx_it.c
 */
//#define vPortSVCHandler								SVC_Handler
//#define xPortPendSVHandler							PendSV_Handler
//#define xPortSysTickHandler							SysTick_Handler

/* Allow system call from within FreeRTOS kernel only. */
#define configENFORCE_SYSTEM_CALLS_FROM_KERNEL_ONLY	1

/* STM32H743 has 16 MPU regions and therefore it is necessary to configure
 * configTOTAL_MPU_REGIONS correctly. */
#define configTOTAL_MPU_REGIONS						16

/* The default TEX,S,C,B setting marks the SRAM as shareable and as a result,
 * disables cache. Do not mark the SRAM as shareable because caching is being
 * used. TEX=0, S=0, C=1, B=1. */
#define configTEX_S_C_B_SRAM						( 0x03UL )

#endif /* FREERTOS_CONFIG_H */

I have increased memory configuration, but this issue remains.

Any pointers to what is occurring would be much appreciated.

Set configCHECK_FOR_STACK_OVERFLOW to 2 in your FreeRTOSConfig.h - currently it is 0.

These pages provide some tips for RAM constrained systems - but be aware this is very old documentation. https://www.freertos.org/tutorial/index.html

Historically we provided co-routines for RAM constrained systems, like the first Cortex-M devices that had a tiny amount of RAM - but generally these days devices on which FreeRTOS runs have more memory so co-routines were deprecated some time back and have not been maintained.

I added the stack overflow check and a hook function, however, it is not called, just get the same hard fault.

Are you sure you are using the appropriate port for your hardware? Didn’t you write it’s an M0?

@RAc Yes I am using the correct port. The configuration file is a generic one and works just fine on other M0 systems.

which heap management are you using?

“which heap management are you using?”

heap_4 is used.

well then, it’s time to show us your linker command and map files…

MorningClock_M2.zip (22.3 KB)
Here are the MAP and Linker script.

That looks ok so far… what is the value in the first location of your IVT, ie where will the initial stack pointer at reset time point to?

At location 0x0800000 I see 0x20001000 and when the code stops at the entry to main the SP is 0x20000ff8.

Also looks valid.

Next thing I would do is inspect the ready task list at the time you call vTaskDelay(). From what you write it may be the case that either no idle task is properly configured, so the context switch after the wait() wouldn’t have anything to switch to, or the service interrupt is not invoked in a valid task context.

Need some help knowing what to examine please.

BTW I’d also #define configUSE_PORT_OPTIMISED_TASK_SELECTION 1
However, are you sure that the essential handlers like SVC_Handler etc. are correctly installed ? Can you step into and trough start of the scheduler resp. is your initial task started ? Can you set breakpoints into those handlers ?
Depending on your setup (using STM HAL ?) this post might be interesting, too.

Yes, the essential handlers are in place.

Stepping through starting the scheduler shows the Idle task being created without error.

I have also stepped through the vTaskDelay of my test task and the hard fault occurs at the end of the call to “portYIELD_WITHIN_API”.

are you positive that your service isr runs at the lowest possible pri?

I have not changed priorities from those generated by CubeMX.

It doesn’t look like you are using FreeRTOSConfig.h generated by CubeMX. If you use that version, do the symptoms change? The version you posted has errors relating to interrupt priorities (the STM32F038 has only 2 interrupt priority bits implemented) and has a suspicious note about vector installations.