# Semaphore doesn't work on STM32F103 **URL:** \ **Category:** Kernel\ **Tags:** debug\ **Created:** [June 30, 2022, 11:32am UTC](https://forums.freertos.org/t/semaphore-doesnt-work-on-stm32f103/15359 "2022-06-30T11:32:58Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Daliwan](https://avatars.discourse-cdn.com/v4/letter/d/db5fbb/32.png) [@Daliwan](https://forums.freertos.org/u/Daliwan)\ **Post date:** [June 30, 2022, 11:32am UTC](https://forums.freertos.org/t/semaphore-doesnt-work-on-stm32f103/15359/1 "2022-06-30T11:32:58Z")
I am new in trying freeRTOS. I am trying to make a simple project in MDK: creat two tasks and a timer. From the timer handler give a semaphore and one task take it and print a string. Without using semaphore, the project works normally. But when the semaphore is added, though the project can be compiled without error, it doesn’t work after it is downloaded into the board, there is not any printing from the board. I tried to use debug and find it stopped at hardfault. The following is the pictures of the projects. Please help me to find what happened. Thank you. The following are the programs: /\* main file \*/ ```auto #include "stm32f10x.h" #include "stm32f10x_tim.h" #include "stm32f10x_conf.h" #include "stm32f10x_gpio.h" #include "stm32f10x_usart.h" #include "FreeRTOS.h" #include "task.h" #include "queue.h" #include "semphr.h" #include "list.h" #include "misc.h" #include "portable.h" #include "FreeRTOSConfig.h" #include "usart1.h" #include "timerConfig.h" static void vUART1_1_Task(void *pvParameters); static void vUART1_2_Task(void *pvParameters); SemaphoreHandle_t xBinarySemaphore; int main(void) { USART1_Config(); TIM2_Init(); xBinarySemaphore = xSemaphoreCreateBinary(); if (xBinarySemaphore != NULL) { xTaskCreate(vUART1_1_Task, (const portCHAR*)"UART1_1", configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL ); xTaskCreate(vUART1_2_Task, (const portCHAR*)"UART1_2", configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL ); vTaskStartScheduler(); } return 0; } void vUART1_1_Task(void *pvParameters) { TickType_t xDelay = pdMS_TO_TICKS(2000); while(1) { printf("\r\n This is task1 ! \r\n"); vTaskDelay(xDelay); //ÑÓʱ2s } } void vUART1_2_Task(void *pvParameters) { while(1) { if(xSemaphoreTake(xBinarySemaphore, portMAX_DELAY)) { printf("Semaphore works!\n\r"); } } // TickType_t xDelay = pdMS_TO_TICKS(2000); // while(1) // { // printf("\r\n This is task2 !!! \r\n"); // vTaskDelay(xDelay); //ÑÓʱ2s // } } ``` /_timer configure file_/ ```auto #include "FreeRTOS.h" #include "semphr.h" #include "timerConfig.h" #include "misc.h" #include "usart1.h" #include "stm32f10x_tim.h" void TIM2_Init(void) { TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure; NVIC_InitTypeDef NVIC_InitStructure; RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE); TIM_TimeBaseStructure.TIM_Period = TIM2_Period; TIM_TimeBaseStructure.TIM_Prescaler = TIM2_Prescaler; TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1; TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure); TIM_ITConfig(TIM2,TIM_IT_Update,ENABLE ); NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn; NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0; NVIC_InitStructure.NVIC_IRQChannelSubPriority = 3; NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; NVIC_Init(&NVIC_InitStructure); TIM_Cmd(TIM2, ENABLE); / } void TIM2_IRQHandler(void) { extern SemaphoreHandle_t xBinarySemaphore; BaseType_t xHigherPriorityTaskWoken; if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET) { TIM_ClearITPendingBit(TIM2, TIM_IT_Update ); xHigherPriorityTaskWoken = pdTRUE; xSemaphoreGive(xBinarySemaphore); portYIELD_FROM_ISR(xHigherPriorityTaskWoken); // printf("\r\n Timer !!! \r\n"); } } ``` ---
**Author:** ![RAc](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rac/32/1389_2.png) [@RAc](https://forums.freertos.org/u/RAc)\ **Post date:** [June 30, 2022, 11:44am UTC](https://forums.freertos.org/t/semaphore-doesnt-work-on-stm32f103/15359/2 "2022-06-30T11:44:40Z")
Please check your stack sizes, minimal may overflow. ---
**Author:** ![Daliwan](https://avatars.discourse-cdn.com/v4/letter/d/db5fbb/32.png) [@Daliwan](https://forums.freertos.org/u/Daliwan)\ **Post date:** [June 30, 2022, 12:05pm UTC](https://forums.freertos.org/t/semaphore-doesnt-work-on-stm32f103/15359/3 "2022-06-30T12:05:55Z")
I changed the stacksize of the two tasks, and follow the debug, find it run to hardFault\_handler directly from TIM2\_init(). I wonder if there is anything wrong with the timer initiation? but I checked it and can not find problem. What’s more, it can work when the semaphore was commeted out. ---
**Author:** ![RAc](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rac/32/1389_2.png) [@RAc](https://forums.freertos.org/u/RAc)\ **Post date:** [June 30, 2022, 12:15pm UTC](https://forums.freertos.org/t/semaphore-doesnt-work-on-stm32f103/15359/4 "2022-06-30T12:15:09Z")
Where and how do you create the semaphore? You shoul check for a null handle before accessing it… edit: please ignore, i found it… another take: Your init code may be enabling interrupts too early. They must remain disabled until scheduler start ---
**Author:** ![aggarg](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/aggarg/32/4245_2.png) [@aggarg](https://forums.freertos.org/u/aggarg)\ **Post date:** [June 30, 2022, 12:21pm UTC](https://forums.freertos.org/t/semaphore-doesnt-work-on-stm32f103/15359/5 "2022-06-30T12:21:37Z")
One possible reason is that interrupt is firing before semaphore is created. Try changing the main to the following: ```auto int main(void) { xBinarySemaphore = xSemaphoreCreateBinary(); if (xBinarySemaphore != NULL) { xTaskCreate(vUART1_1_Task, (const portCHAR*)"UART1_1", configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL ); xTaskCreate(vUART1_2_Task, (const portCHAR*)"UART1_2", configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL ); USART1_Config(); TIM2_Init(); vTaskStartScheduler(); } return 0; } ``` Also, you are calling the `xSemaphoreGive` API from an ISR while you should call `xSemaphoreGiveFromISR`: ```auto void TIM2_IRQHandler(void) { extern SemaphoreHandle_t xBinarySemaphore; BaseType_t xHigherPriorityTaskWoken = pdFALSE; if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET) { TIM_ClearITPendingBit(TIM2, TIM_IT_Update ); xSemaphoreGiveFromISR(xBinarySemaphore, &( xHigherPriorityTaskWoken )); portYIELD_FROM_ISR(xHigherPriorityTaskWoken); } } ``` ---
**Author:** ![Daliwan](https://avatars.discourse-cdn.com/v4/letter/d/db5fbb/32.png) [@Daliwan](https://forums.freertos.org/u/Daliwan)\ **Post date:** [June 30, 2022, 12:36pm UTC](https://forums.freertos.org/t/semaphore-doesnt-work-on-stm32f103/15359/6 "2022-06-30T12:36:01Z")
Really thank you guys, you are great! I put the TIM\_Init() into a task and then it works. Just like you said, the interrupt runs before the semaphore is created. I don’t know this rule. Thank you very much. ---
**Author:** ![hs2](https://avatars.discourse-cdn.com/v4/letter/h/a4c791/32.png) [@hs2](https://forums.freertos.org/u/hs2)\ **Post date:** [June 30, 2022, 12:59pm UTC](https://forums.freertos.org/t/semaphore-doesnt-work-on-stm32f103/15359/7 "2022-06-30T12:59:47Z")
It’s not exactly a rule - it’s just about using an uninitialized variable. If `xBinarySemaphore` is not yet created but accidentally used (too early) in the ISR, an invalid handle is used which is a license to crash 😉 ---
**Author:** ![Daliwan](https://avatars.discourse-cdn.com/v4/letter/d/db5fbb/32.png) [@Daliwan](https://forums.freertos.org/u/Daliwan)\ **Post date:** [June 30, 2022, 1:10pm UTC](https://forums.freertos.org/t/semaphore-doesnt-work-on-stm32f103/15359/8 "2022-06-30T13:10:23Z")
Yeah, I see. When the timer start, the IRQ handler works and the xBinarySemaphore was called, but it is still not created. I was accustomed to initializing everything in the beginning and made this mistake. Thank you very much!