External SDRAM with Blackfin and FreeRTOS

Question

I have a custom board with Blackfin DSP and External SDRAM 64 MB and FreeRTOS. Reading from SDRAM using task with priority 6. In a test I read about 20000 words. Each word is twice consecutively, some the of words read do not match between the first read and second read. The two reads are done immediately one after the other.

If I repeat the same test using the highest priority, I do not get any errors.

If do the same test without FreeRTOS, I do not get any errors.

For normal operations I need to keep reading the SDRAM at low priority.

Any suggestions how to solve this issue ?d Where I need to look to find the cause of this issue ?

Thanks.

Answer 1

You probably have memory corruption due to the task switch of the RTOS.

An easy fix is to use the CRITICAL section of the freeRTOS while you do your read to avoid context switch.

A correct fix is to use Queues and Mutexes to pass data around, but without seeing code it's difficult to give a more precise answer.