nRF52840 nrfx_uart TX working, RX not

RE: nRF52840 nrfx_uart TX working, RX not

Håkon Alseth — Thu, 31 Jan 2019 07:54:50 GMT

Hi,

Great job on finding the source of the issue! Things like these are hard to debug, so kudos on finding the source this fast. Have a nice day, and contact us again if there's any more issues/questions 🙂

Kind regards,

Håkon

RE: nRF52840 nrfx_uart TX working, RX not

nrarmen — Wed, 30 Jan 2019 19:26:47 GMT

Confirmed: The problem was calling nrfx_uart_rx_enable during an init routine while the other microcontroller was asleep (and thus RX line low). This cause ERRORSRC to read 0x0C (and eventually 0x0D) before I tried nrfx_uart_rx.

The solution was to call nrfx_uart_rx_enable immediately before nrfx_uart_rx (in blocking mode) and then for good measure, call nrfx_uart_rx_disable immediate after nrfx_uart_rx returned.

Thanks for the help, Håkon!

RE: nRF52840 nrfx_uart TX working, RX not

nrarmen — Wed, 30 Jan 2019 18:04:56 GMT

TX is P0.06 and RX is P0.08

Regarding ERRORSRC: The error happens on the first UART transmission / reception and that's when I see all 3 flags noted above are set. I don't read this register in code. I was just reading it through the debugger after I hit the breakpoint when the function fails.

The nrfx_uart_rx function returns NRFX_ERROR_INTERNAL. The contents of the buffer passed to nrfx_uart_rx is garbage, though I'm not sure if that's from heap allocation (malloc'd to 16 bytes, never freed) or nrfx_uart_rx putting bytes there. I'm requesting 10 bytes of data to be read (nBytes = 10), which is the entire length of the response I'm expecting.

The function returns at nrfx_uart.c line 442 (line 27 below). Here's the snippet for your convenience:

bool rxrdy;
bool rxto;
bool error;
do
{
    do
    {
        error = nrf_uart_event_check(p_instance->p_reg, NRF_UART_EVENT_ERROR);
        rxrdy = nrf_uart_event_check(p_instance->p_reg, NRF_UART_EVENT_RXDRDY);
        rxto  = nrf_uart_event_check(p_instance->p_reg, NRF_UART_EVENT_RXTO);
    } while ((!rxrdy) && (!rxto) && (!error));

    if (error || rxto)
    {
        break;
    }
    rx_byte(p_instance->p_reg, p_cb);
} while (p_cb->rx_buffer_length > p_cb->rx_counter);

p_cb->rx_buffer_length = 0;
if (error)
{
    err_code = NRFX_ERROR_INTERNAL;
    NRFX_LOG_WARNING("Function: %s, error code: %s.",
                     __func__,
                     NRFX_LOG_ERROR_STRING_GET(err_code));
    return err_code;
}

Update 1: ERRORSRC is set to 12 when rx_enable is called. This is probably expected because RX pin is not high at this time because the other microcontroller is asleep. I will move this call after the other microcontroller is awake.

RE: nRF52840 nrfx_uart TX working, RX not

Håkon Alseth — Wed, 30 Jan 2019 15:04:29 GMT

Hi,

Which GPIOs are you using for TXD and RXD?

[quote user=""]Reading address 0x40002480 (UART0 ERRORSRC, right?) gives a value of 0x0D, i.e. BREAK, ERROR, and OVERRUN are all present.[/quote]

This register accumulates errors, so if you do not clear it, it might show errors from an earlier session.

Remember to clear this register after reading.

What does the nrfx_uart_rx() function return?

[quote user=""]Do you have any ideas about what else I can try to get nrfx_uart_rx to work?[/quote]

What do you pass as nBytes into ::read()? Have you tried setting this to poll one-and-one byte to see if that makes any difference?

Have you debugged the solution to see where it returns in the function?

Kind regards,

Håkon