mutex - Uart dma receive interrupt stops receiving data after several minutes

Question

I have a project that I have used stm32f746g discovery board. It receives data with fixed size from Uart sequentially and to inform application about each data receive completed, dma callback is used (HAL_UART_RxCpltCallback function). It works fine at the beginning but after several minutes of running, the dma callback stops to be called, and as a result, the specified parameter value doesn't get updated. Because the parameter is used in another thread too (actually a rtos defined timer), I believe this problem is caused by lacking of thread safety. But my problem is that mutex and semaphore don't be supported in ISRs and I need to protect my variable in dma callback which is an interrupt routine. I am using keil rtx to handle multithreading and the timer I use is osTimer that is defined in rtx. How can I handle the issue?

Answer 1

Generally, only one thread should communicate with the ISR. If multiple threads are accessing a variable shared with an ISR, your design is wrong and needs to be fixed. In case of DMA, only one thread should access the buffer.

You'll need to protect the variables shared between that thread and the ISR - not necessarily with a mutex/semaphore but perhaps with something simpler like guaranteeing atomic access (best solution if possible), or by using the non-interrruptable abilitiy that many ISRs have. Example for simple, single-threaded MCU applications. Alternatively just temporarily disable interrupts during access, but that may not be possible, depending on real-time requirements.