Rerouting printf() to UART

[newUser]

Hi,

Currently our system is using printf() to print some debug messages to the Segger debug terminal.
Now we would like to reroute these messages to a UART port.

We are already using 1 UART for communication with chip on the board. We would like to use the other UART for the debug messages.

In our sdk_config.h we changed NRF_LOG_BACKEND_RTT_ENABLED from 1 to 0, and NRF_LOG_BACKEND_UART_ENABLED from 0 to 1.
Furthermore, we set NRF_LOG_BACKEND_UART_TX_PIN. For now, we left NRF_LOG_BACKEND_UART_BAUDRATE at 30801920

Unfortunately, after these changes the UART that we were previously already using successfully is no longer working.
This is coming into a conditional breakpoint:

    app_uart_comm_params_t const uart1_settings =
    {
        .rx_pin_no    = UART1_TX_PIN,
        .tx_pin_no    = UART1_RX_PIN,
        .rts_pin_no   = RTS_PIN_NUMBER,
        .cts_pin_no   = CTS_PIN_NUMBER,
        .flow_control = APP_UART_FLOW_CONTROL_DISABLED,
        .use_parity   = false,
        .baud_rate    = UART_BAUDRATE_BAUDRATE_Baud115200
    };
    APP_UART_FIFO_INIT(&uart1_settings,
                       UART_RX_BUF_SIZE,
                       UART_TX_BUF_SIZE,
                       uart1_event_handle,
                       APP_IRQ_PRIORITY_LOWEST,
                       err_code);
    APP_ERROR_CHECK(err_code);       // check if UART is setup without errors

What are we missing?

[Vidar Berg]

Hello,

Maybe both are trying to use the same UARTE instance? The Logger module  UART backend is hardcoded to use the UARTE0, same  instance as the app_uart library uses by default.

Please make sure APP_UART_DRIVER_INSTANCE is set to '1' in your sdk_config.h file. This will make APP_UART_FIFO_INIT() initialize UARTE1.

Best regards,

Vidar

[newUser]

Thank you Vidar Berg, this got us a bit further. We see all NRF_LOG messages going to UART now.
However, we would like printf() to go to UART too. 

What extra step do we need?

[Vidar Berg]

It should work if you include our retarget.c file your project (\components\libraries\uart\retarget.c). Printf will go out on UARTE1 if everything works.

[newUser]

I have included the retarget.c file.
When I add the following to sdk_config.h file:
#ifndef RETARGET_ENABLED
#define RETARGET_ENABLED 1
#endif
I get a breakpoint with the following error:
<error> app: ERROR 3735928559 [Unknown error code] at /sdk/modules/nrfx/drivers/src/nrfx_uart.c:28014:33:01.012 -> PC at: 0x0002BC9714:33:01.012 -> <error> app: End of error report
Line 280:
NRFX_ASSERT(p_cb->state == NRFX_DRV_STATE_INITIALIZED);

[Vidar Berg]

nrfx_uart.c:nrfx_uart_tx() shouldn't get called when using UARTE1, so I'm not sure why you are getting the assert. Could you try to place the 2 breakpoints as shown in the screenshot below, then check if the UARTE instance is 0 or 1 when nrf_uart_tx() gets called in your application?