STM32F4 Interrupt + FreeRTOS

Kernel
1

fjullien wrote on Thursday, July 24, 2014:

Hello,

I know it is a recurrent topic but after I read all a could find about this, I still have a problem using interrupts in combination with FreeRTOS.

I’m using libopencm3. On my board I can run the libopencm3 USB stack in interrupt mode without problem. But, if I run a FreeRTOS task, it mess up things (I get my device always connect/disconnect). I didn’t look at the root cause of this connect/disconnect problem. However I suspect the usbd_poll function (called in the USB ISR) to be preempted. My ISR is as simple as this:

void otg_fs_isr(void)
{
usbd_poll(msc_dev);
}

And my task (I know, there is no vTaskDelay):

static portTASK_FUNCTION(vLEDFlashTask, pvParameters)
{
(void) pvParameters;
int i = 0;

for(;:wink: {
// It waits for TX reg empty then send the char
usart_send_blocking(USART1, ‘A’);
gpio_toggle(GPIOG, GPIO6);
}
}

I did setup all the priority bits as pre-emption priority:

// Same as NVIC_PriorityGroupConfig( NVIC_PriorityGroup_4 )
scb_set_priority_grouping(SCB_AIRCR_PRIGROUP_GROUP16_NOSUB);

My ISR priority is 1:

nvic_set_priority(NVIC_OTG_FS_IRQ, 1);

I also tried to change the system handler priority for systick, svcall and pendsv (as for what I understood are priority ‘0’ by default):

SCB_SHPR(SCB_SHPR_PRI_11_SVCALL) = 12;
SCB_SHPR(SCB_SHPR_PRI_14_PENDSV) = 13;
SCB_SHPR(SCB_SHPR_PRI_15_SYSTICK) = 14;

However if I remove the usart_send_blocking call in the task, it works as expected. Anyone as a clue ?

Thanks in advance,

Franck.

2

rtel wrote on Thursday, July 24, 2014:

I’m afraid I don’t know anything about this library, or its implementation. Are you aware that ST provide STM32Cube? ( http://www.st.com/stm32cube ) That has USB drivers and FreeRTOS included.

My ISR priority is 1:

Is your interrupt making use of FreeRTOS API functions? If so then I can’t image 1 will be a correct value for this. What is configMAX_SYSCALL_INTERRUPT_PRIORITY set to?

I also tried to change the system handler priority for
systick, svcall and pendsv (as for what I understood are
priority ‘0’ by default):

The systick and pendsv priorities will be overwritten to their correct values by FreeRTOS anyway, and the svcall priority is not used other than to kick the kernel off.

Regards.

3

fjullien wrote on Thursday, July 24, 2014:

My interrupt does not use FreeRTOS API.

AFAIR, configMAX_SYSCALL_INTERRUPT_PRIORITY is set to 5 (I don’t have access to my code right now).

Anyway, I think I’ll move to STM32CubeMX. I can’t spend too much time here. I just wanted to avoid STMCube, Windows and Atollic :wink:

I’ll get back to this later.

Thanks for your answer anyway.

Franck.