FreeRTOS+STM32F302, no HAL

I am setting up an application running on a custom board with the STM32F302RC (Cortex M4F, floating point enabled). I’m using the LL drivers only (no HAL).

I haven’t used FreeRTOS much in the past, and never on the ST family. My simple test app configures the processor, creates a single task, and starts it.

int main() {
    platform_init();
    SWO_PrintString("hello world!\n",0);
    startUartRx();

    xTaskCreate(defaultTask, "Default", 32, NULL,tskIDLE_PRIORITY+1, NULL);
    xPortStartScheduler();

    while (1) {

    }
    return 0;
}

This is the task itself:

static void defaultTask(void * params) {
    }
    for (;;) {
        vTaskDelay(pdMS_TO_TICKS(500));
        LL_GPIO_SetOutputPin(aux_GPIO_Port, aux_Pin);

        vTaskDelay(pdMS_TO_TICKS(500));
        LL_GPIO_ResetOutputPin(aux_GPIO_Port, aux_Pin);
    }
}

And this doesn’t work. Nothing seems to happen, and when I stop in the debugger, I’m always at the call to taskSELECT_HIGHEST_PRIORITY_TASK in vTaskSwitchContext(), tasks.c:

...
		#endif /* configGENERATE_RUN_TIME_STATS */

		/* Check for stack overflow, if configured. */
		taskCHECK_FOR_STACK_OVERFLOW();

		/* Select a new task to run using either the generic C or port
		optimised asm code. */
		taskSELECT_HIGHEST_PRIORITY_TASK(); // <---- Always here
		traceTASK_SWITCHED_IN();

		#if ( configUSE_NEWLIB_REENTRANT == 1 )
		{
			/* Switch Newlib's _impure_ptr variable to point to the _reent
			structure specific to this task. */
			_impure_ptr = &( pxCurrentTCB->xNewLib_reent );
		}
		#endif /* configUSE_NEWLIB_REENTRANT */
	}
...

However, if I create a second empty task, now the first task works and my GPIO output toggles on and off:

int main() {
    platform_init();
    SWO_PrintString("hello world!\n",0);
    startUartRx();

    xTaskCreate(defaultTask, "Default", 32, NULL,tskIDLE_PRIORITY+1, NULL);
    xTaskCreate(secondTask, "Second", 32, NULL,tskIDLE_PRIORITY, NULL); //<---- 2nd task, now first task runs
    xPortStartScheduler();

    while (1) {

    }
    return 0;
}

void secondTask(void * params) {
    for (;;) {
    }
}

Any thoughts? Seems like an issue with my interrupt configuration, since vTaskSwitchContext is called from PendSV_Handler.

My FreeRTOSConfig.h:

/*
 * FreeRTOS Kernel V10.0.1
 * Copyright (C) 2017 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

/*-----------------------------------------------------------
 * this is a template configuration files
 *
 * These definitions should be adjusted for your particular hardware and
 * application requirements.
 *
 * These parameters and more 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 stdint is only used by the compiler, and not the assembler. */
#if defined(__ICCARM__) || defined(__CC_ARM) || defined(__GNUC__)
 #include <stdint.h>
 extern uint32_t SystemCoreClock;
#endif

/*  CMSIS-RTOSv2 defines 56 levels of priorities. To be able to use them
 *  all and avoid application misbehavior, configUSE_PORT_OPTIMISED_TASK_SELECTION
 *  must be set to 0 and configMAX_PRIORITIES to 56
 *
 */
/* #define configUSE_PORT_OPTIMISED_TASK_SELECTION	0*/
/* #define configMAX_PRIORITIES					( 56 ) */
#define configUSE_PREEMPTION              1
#define configUSE_IDLE_HOOK               0
#define configUSE_TICK_HOOK               0
#define configMAX_PRIORITIES              (7)
#define configSUPPORT_STATIC_ALLOCATION   0
#define configCPU_CLOCK_HZ                (SystemCoreClock)
#define configTICK_RATE_HZ                ((TickType_t)1000)
#define configMINIMAL_STACK_SIZE          ((uint16_t)128)
#define configTOTAL_HEAP_SIZE             ((size_t)(4096))
#define configMAX_TASK_NAME_LEN           (16)
#define configUSE_TRACE_FACILITY          1
#define configUSE_16_BIT_TICKS            0
#define configIDLE_SHOULD_YIELD           1
#define configUSE_MUTEXES                 1
#define configQUEUE_REGISTRY_SIZE         8
#define configCHECK_FOR_STACK_OVERFLOW    0
#define configUSE_RECURSIVE_MUTEXES       1
#define configUSE_MALLOC_FAILED_HOOK      0
#define configUSE_APPLICATION_TASK_TAG    0
#define configUSE_COUNTING_SEMAPHORES     1
#define configGENERATE_RUN_TIME_STATS     0

/* Co-routine definitions. */
#define configUSE_CO_ROUTINES           0
#define configMAX_CO_ROUTINE_PRIORITIES (2)

/* Software timer definitions. */
#define configUSE_TIMERS             0
#define configTIMER_TASK_PRIORITY    (2)
#define configTIMER_QUEUE_LENGTH     10
#define configTIMER_TASK_STACK_DEPTH (configMINIMAL_STACK_SIZE * 2)

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

/*------------- CMSIS-RTOS V2 specific defines -----------*/
/* When using CMSIS-RTOSv2 set configSUPPORT_STATIC_ALLOCATION to 1
 * is mandatory to avoid compile errors.
 * CMSIS-RTOS V2 implmentation requires the following defines
 *
#define configSUPPORT_STATIC_ALLOCATION          1   <-- cmsis_os threads are created using xTaskCreateStatic() API
#define configMAX_PRIORITIES                    (56) <-- Priority range in CMSIS-RTOS V2 is [0 .. 56]
#define configUSE_PORT_OPTIMISED_TASK_SELECTION 0    <-- when set to 1, configMAX_PRIORITIES can't be more than 32 which is not suitable for the new CMSIS-RTOS v2 priority range
*/

/* the CMSIS-RTOS V2 FreeRTOS wrapper is dependent on the heap implementation used
 * by the application thus the correct define need to be enabled from the list
 * below
 *
//define USE_FreeRTOS_HEAP_1
//define USE_FreeRTOS_HEAP_2
//define USE_FreeRTOS_HEAP_3
//define USE_FreeRTOS_HEAP_4
//define USE_FreeRTOS_HEAP_5

*/


/* 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        /* 15 priority levels */
#endif

/* The lowest interrupt priority that can be used in a call to a "set priority"
function. */
#define configLIBRARY_LOWEST_INTERRUPT_PRIORITY   0xf

/* 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. */
#define vPortSVCHandler    SVC_Handler
#define xPortPendSVHandler PendSV_Handler

/* IMPORTANT: FreeRTOS is using the SysTick as internal time base, thus make sure the system and peripherials are
              using a different time base (TIM based for example).
 */
#define xPortSysTickHandler SysTick_Handler

#endif /* FREERTOS_CONFIG_H */

Thanks,
Philip

It never fails: you spend hours trying to figure out an issue, finally post something to a forum, and then immediately figure it out yourself.

Obviously, I should be calling vTaskStartScheduler() instead of xPortStartScheduler().