RE: FreeRTOS + UART receive blocks everything

maxv — Sun, 17 Apr 2016 12:02:13 GMT

I haven't got stack overflow checking on.

However, I was wondering if it's common to implement an indepedent task to check on all the other tasks' high water mark, using uxTaskGetStackHighWaterMark?

I'm thinking about printing this information out at runtime.

Update 1:

After doing some more digging, it does look like the legacy UART driver is not compatible with FreeRTOS. This is likely a problem on the Nordic side. It's not a stack size issue. It's probably fixable by using the UARTE non-blocking Rx/Tx, and I'll be trying that path next.

When I trace the problem with gdb, it tells me that the nrf_drv_uart_rx_for_uart gets stuck in a while loop, but the OS should have at some point preempted this, and allowed my other tasks to run:

Program received signal SIGTRAP, Trace/breakpoint trap.
nrf_drv_uart_rx_for_uart (p_data=<optimized out>, length=<optimized out>, second_buffer=<optimized out>) at /home/max/nRF5_SDK_11.0.0_89a8197/components/drivers_nrf/uart/nrf_drv_uart.c:421
421	            } while ((!rxrdy) && (!rxto) && (!error));
(gdb) bt
#0  nrf_drv_uart_rx_for_uart (p_data=<optimized out>, length=<optimized out>, second_buffer=<optimized out>) at /home/max/nRF5_SDK_11.0.0_89a8197/components/drivers_nrf/uart/nrf_drv_uart.c:421
#1  nrf_drv_uart_rx (p_data=p_data@entry=0x20003314 <ucHeap+2524> "", length=length@entry=8 '\b') at /home/max/nRF5_SDK_11.0.0_89a8197/components/drivers_nrf/uart/nrf_drv_uart.c:570
#2  0x0002191e in uart_input_task (arg=<optimized out>) at /home/max/nRF5_SDK_11.0.0_89a8197/examples/ble_peripheral/ble_app_hrs_freertos/main.c:911
#3  0x0001d684 in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

My task creation in main() looks like this, and the code is getting stuck immediately at the launch of uart_input_task, it never runs the tasks specified in the other xTaskCreate calls:

if (pdPASS != xTaskCreate(uart_input_task, "UART Rx", 256, NULL, 1, &m_uart_input_thread))
{
    printf("Out of memory.");
    APP_ERROR_HANDLER(NRF_ERROR_NO_MEM);
}

if (pdPASS != xTaskCreate(uart_output_task, "UART Tx", 256, NULL, 1, &m_uart_output_thread))
{
    printf("Out of memory.");
    APP_ERROR_HANDLER(NRF_ERROR_NO_MEM);
}

if (pdPASS != xTaskCreate(uart_test_task, "Test UART Task", 256, NULL, 1, &m_uart_test_task))
{
    printf("Out of memory.");
    APP_ERROR_HANDLER(NRF_ERROR_NO_MEM);
}

Update 2:

Yes, using the UARTE non-blocking TX/RX seems to work. The UART event handler passed to nrf_drv_uart_init() uses a semaphore to notify the RX task that data has been received, and the RX task sets up another receive using nrf_drv_uart_rx(), then the RX task waits on the semaphore again.

RE: FreeRTOS + UART receive blocks everything

www.FreeRTOS.org — Fri, 15 Apr 2016 17:33:37 GMT

See my reply to this thread, my reply to this one would be very similar.

Your stack looks relatively small - do you have stack overflow checking on?