app_uart_get returns NRF_ERROR_NOT_FOUND, nRF51822 on nRF6310 with RS232

[Eliot Stock]

I want to read a line of text from a UART peripheral. I'm using app_uart.c, not the "simple UART" example code.

My main() looks something like this:

uint8_t line[MAX_CHARS];
uint8_t command[] = "ATI\n";
uint32_t err_code;
uint16_t uart_uid;
app_uart_comm_params_t comm_params;

leds_init();

comm_params.rx_pin_no = RX_PIN_NUMBER;
comm_params.tx_pin_no = TX_PIN_NUMBER;
comm_params.rts_pin_no = NULL;
comm_params.cts_pin_no = NULL;
comm_params.flow_control = APP_UART_FLOW_CONTROL_DISABLED;
comm_params.baud_rate = UART_BAUDRATE_BAUDRATE_Baud38400;
		
err_code = app_uart_init(&comm_params, NULL, &uart_event_handler, APP_IRQ_PRIORITY_HIGH, &uart_uid);
APP_ERROR_CHECK(err_code);
		
uart_getline(line);

for (;;)
{
}

and my implementation of uart_getline() is:

static void uart_getline(uint8_t * line)
{
	uint_fast8_t i = 0;
	uint8_t ch;
	uint32_t err_code;

	do {
		err_code = app_uart_get(&ch);
		APP_ERROR_CHECK(err_code);

		line[i++] = ch;
	}
	while (ch != '\n');
}

My uart_event_handler() function does nothing.

I have the peripheral connected to the RS-232 port on the motherboard and the red RS232 switch set to on. My pins P2.0 and P2.1 are connected with jumpers to the TXD and RXD pins on port P15. I haven't connected anything to the RTS and CTS pins (not using hardware flow control).

I can connect to the peripheral from a hyperterminal session and see output. It's a simple GPS eval board. I know it works fine with no flow control, 38400 baud, 8N1.

What I'm seeing is that in app_uart_get...

uint32_t app_uart_get(uint8_t * p_byte)
{
    if (m_rx_byte == BYTE_INVALID)
    {
        return NRF_ERROR_NOT_FOUND;
    }

    *p_byte   = m_rx_byte;
    m_rx_byte = BYTE_INVALID;

    return NRF_SUCCESS;
}

... is that m_rx_byte is always BYTE_INVALID

What could be causing this?

[Pål Håland]

Hi Eliot,

It looks like you are trying to pull out a byte before you have received an interrupt telling you that there is data available to be read out.

If you don't want to return from your function until you have received a line, then you should just go to sleep if the error code is NRF_ERROR_NOT_FOUND.

static void uart_getline(uint8_t * line)
{
	uint8_t i = 0, ch = 0;
	uint32_t err_code;

	do {
		err_code = app_uart_get(&ch);
                if (NRF_ERROR_NOT_FOUND == err_code)
                {
                    sd_app_event_wait();
                }
                else if (NRF_SUCCESS == err_code)   
                {
		    line[i++] = ch;
                }
                else
                {
		    APP_ERROR_CHECK(err_code);
                }
	}
	while (ch != '\n');
}

BR Pål

[Eliot Stock]

Thanks for this. I'm having trouble finding the implementation of sd_app_evt_wait(). Have included nrf_soc.h in my main.c but presumably there's a .c source file I need in my project too?

compiling main.c...
src\main.c(960): warning:  #223-D: function "sd_app_evt_wait" declared implicitly
...
linking...
.\device-nordic.axf: Error: L6218E: Undefined symbol sd_app_evt_wait (referred from main.o).
".\device-nordic.axf" - 1 Errors, 16 Warning(s).

[Eliot Stock]

Found the problem: the function sd_app_evt_wait() in your code snippet should have been sd_app_event_wait(), I think.

So this builds and runs OK but I'm still not getting anything but NRF_ERROR_NOT_FOUND back from app_uart_get() no matter how long I wait. I know the UART peripheral is sending data.

[Pål Håland]

I updated my codeblock with sd_app_event_wait(),

Related to not receiving data on the UART, have you connected it to the correct pins? Try to see if you are able to get a interrupt in the UART interrupt handler UART0_IRQHandler inside the app_uart.c

[Pål Håland]

Have you been able to resolve this issue yet?