Stm32 freertos, all variable can not be change in my project

Question

I don't understand why freertos do not allow to change extern variables (myData) here is my poject

file main.c

uint16_t Mydata = 0;

main()
{
    System_Init();
    xTaskCreate(Task1, (const char*)"Task1", 100, NULL, 4, NULL);   
    xTaskCreate(Task2, (const char*)"Task2", 100, NULL, 3, NULL);   
    vTaskStartScheduler();
}

file Task1.c

extern uint16_t Mydata;

void Task1(void *p)
{ 
    while(1)
    {
        vTaskDelay(10);
        printf("Result: %d", Mydata);
    }
}

file Task2.c

extern uint16_t Mydata;

void Task2(void *p)
{
    while(1)
    {
       Mydata++;
       vTaskDelay(10);
    }
}

but the result is never correct

most of result is like "13842930", "-18234952", or something like that !

can anyone tell me why? (I'm sorry because of my bad English) thank for your help !

Freddie Chopin Freddie Chopin · Accepted Answer · 2017-02-16T11:30:52

You cannot use %d for printing a value of uint16_t. %d expects an int. You either have to cast your value to int in the printf() call (printf("Result: %d", (int)Mydata);), or use proper specifier (printf("Result: %" PRIu16 "", Mydata);). The second solution might not be supported by your toolchain.

http://en.cppreference.com/w/cpp/io/c/fprintf

Your variable should be declared volatile, otherwise compiler may as well read it once an never update the value from RAM.

Stm32 freertos, all variable can not be change in my project

1 Answers