Interrupt priorities on FreeRTOS ports without configKERNEL_INTERRUPT_PRIORITY

Kernel
#1

vectorl wrote on Tuesday, April 29, 2014:

I’m using the STM32F0 port with IAR. I’m trying to understand the RTOS interrupt priority in relation to the interrupt priority of the STM32F0. The port does not define configKERNEL_INTERRUPT_PRIORITY or configMAX_SYSCALL_INTERRUPT_PRIORITY in FreeRTOSConfig.h.

However, configKERNEL_INTERRUPT_PRIORITY is defined to 0 in the port.c but it doesn’t look to be used and is there just as backwards compatibility.

The STM32F0 has 4 interrupt priorities (0-3). I’m trying to figure out if I’m setting my ISR (non-RTOS and RTOS-calls-from) priorities correctly but I’m not sure what the priority the RTOS is running at. Help?

#2

davedoors wrote on Tuesday, April 29, 2014:

I don’t think the M0 has a base pri register, and looking at the source code I see interrupts are disabled in critical sections rather than masked, so I think that must be right. The set/clear interrupts from ISR macros are also globally disabling/enabling so in summary it looks like you can use any interrupt priority you like but keep the tick and pend sv interrupts at the lowest priority.

#3

vectorl wrote on Tuesday, April 29, 2014:

Thanks, That makes sense. So if I have an isr that calls a FreeRTOS api, does it also have to set at the lowest priority? or does it not matter because it’s not masked?

#4

davedoors wrote on Tuesday, April 29, 2014:

From looking at the source code I would say it can run at any priority.

On M3 and M4 critical sections in interrupts mask priorities up to a set threshold, and interrupts using the API have to keep below that threshold. On M0 critical sections in interrupts mask all priorities, so there is no threshold to keep below.

#5

vectorl wrote on Tuesday, April 29, 2014:

I guess that means no interrupt can preempt the FreeRTOS critical sections. I will keep that in mind as I design my system. Good info. Thanks.