Marvee Amasi Posts - Answer Overflow

Marvee Amasi

•Created by Marvee Amasi on 5/26/2024 in #code-review

Modifying FreeRTOS Interrupt Priorities After Scheduler Initialization

Hey everyone @Middleware & OS , I'm neck-deep in an RTOS project using FreeRTOS. I need to read and potentially modify interrupt priorities after the FreeRTOS scheduler has been kicked off with vTaskStartScheduler(). The issue is, NVIC_GetPriority(DMA1_Channel4_IRQn) seems to behave differently depending on when I call it.

#include <FreeRTOS.h>
#include <queue.h>
#include <task.h>
#include "stm32f4xx_hal.h" 

static void vTest_NVIC(void *pvParameters) {
    tprintf("\r\nTask Started...");

    while (1) {
        taskENTER_CRITICAL(); 
        uint32_t priority = NVIC_GetPendingIRQ(DMA1_Channel4_IRQn) ?
                             NVIC_GetPriority(DMA1_Channel4_IRQn) : portMAX_DELAY;
        tprintf("\r\nCurrent priority (if pending): %d", (int)priority);
        taskEXIT_CRITICAL();
        vTaskDelay(pdMS_TO_ICKS(3000)); 
    }
}

int main(void) {
    portBASE_TYPE xReturn;
    HAL_NVIC_SetPriorityGrouping(NVIC_PRIORITYGROUP_4); 
    HAL_NVIC_SetPriority(DMA1_Channel4_IRQn, 11, 0); 
    tprintf("\r\nInitial priority: %d", (int)NVIC_GetPendingIRQ(DMA1_Channel4_IRQn) ?
    NVIC_GetPriority(DMA1_Channel4_IRQn) : portMAX_DELAY);
    vTaskStartScheduler();
}

#include <FreeRTOS.h>
#include <queue.h>
#include <task.h>
#include "stm32f4xx_hal.h" 

static void vTest_NVIC(void *pvParameters) {
    tprintf("\r\nTask Started...");

    while (1) {
        taskENTER_CRITICAL(); 
        uint32_t priority = NVIC_GetPendingIRQ(DMA1_Channel4_IRQn) ?
                             NVIC_GetPriority(DMA1_Channel4_IRQn) : portMAX_DELAY;
        tprintf("\r\nCurrent priority (if pending): %d", (int)priority);
        taskEXIT_CRITICAL();
        vTaskDelay(pdMS_TO_ICKS(3000)); 
    }
}

int main(void) {
    portBASE_TYPE xReturn;
    HAL_NVIC_SetPriorityGrouping(NVIC_PRIORITYGROUP_4); 
    HAL_NVIC_SetPriority(DMA1_Channel4_IRQn, 11, 0); 
    tprintf("\r\nInitial priority: %d", (int)NVIC_GetPendingIRQ(DMA1_Channel4_IRQn) ?
    NVIC_GetPriority(DMA1_Channel4_IRQn) : portMAX_DELAY);
    vTaskStartScheduler();
}

- Before calling vTaskStartScheduler(), NVIC_GetPriority(DMA1_Channel4_IRQn) works as expected and reflects the configured priority (11). - However, after the scheduler starts, the function consistently returns 11, regardless of any changes I try to make within the vTest_NVIC task. I've tried using taskENTER_CRITICAL() and taskEXIT_CRITICAL() to ensure thread safety, but it doesn't seem to resolve the issue. What am I missing here? Why does the behavior differ before and after the scheduler starts?

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