Tasks stop when USART ISR priority is defined

Kernel
1

Hi,

I recently made a post about a crash in stream buffer when using ISR. The solution to that crash was defining ISR priority. This worked fine for a while(up to two hours), but later something really strange happens, the app stops running, there is no crash, it just stops.

For debugging purposes I simplified my code not to rely on ISR at all. The ISR is there just for tests, it does nothing. Here it is:

extern "C" void USART3_IRQHandler() {
    USART_ClearITPendingBit(USART3, USART_IT_RXNE);
}

I have also modified my read method not to read data register:

uint8_t Uart3::readByte(char *output, uint32_t timeoutMs) {
    *output = 's';
    return UART_OK;
}

And here is how I enable ISR:

    NVIC_InitTypeDef NVIC_InitStructure;
    NVIC_InitStructure.NVIC_IRQChannel = USART3_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    USART_ITConfig(USART3, USART_IT_RXNE, ENABLE);
    NVIC_Init(&NVIC_InitStructure);
    NVIC_EnableIRQ(USART3_IRQn);
    NVIC_SetPriority(USART3_IRQn, 254);

Now when I comment out NVIC_SetPriority everything works fine, but than I cannot use StreamBuffers. I tried setting various priority numbers, but without luck. Here is how priority is set in FreeRTOSConfig.h:

#define configKERNEL_INTERRUPT_PRIORITY 		255
#define configMAX_SYSCALL_INTERRUPT_PRIORITY 	191

I am using FreeRTOS V10.4.3, latest as of this writing.
Do you guys have any idea what could be happening?

Thanks in advance.

2

Double check how you are using this function. You are passing in the priority shifted into the top most bits (which is what the hardware expects), but I think this function expects the priority to be in the least significant bits - which the shift being performed inside the function itself. RTOS for ARM Cortex-M

Also on the same page note if you are using an STM32 you also have to call NVIC_PriorityGroupConfig( NVIC_PriorityGroup_4 ).

3

This looks like a STM32. AFAIK, most of them have 4 priority bits implemented (F0 series have 2 bits). This means that the parameter you can pass to NVIC_SetPriority() must be in [0-15] interval, 15 being the lowest priority.

A call to NVIC_PriorityGroupConfig() is probably not needed because by default (after reset) all bits are main-priority bits (0 bits for sub-priority).