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?

[newUser]

The instance is 0. Instance 1 is used by our communication chip, after the suggested changes, so indeed we need retarget on 0.

In retarget.c I see that app_uart_put is used, but that function is used to send data to our modem. 
We have also tried replacing app_uart_put with app_uart_put2, which is our function to transmit to the other uart fifo, but this suddenly yields garbage data (we are using the baudrate from the SDK config: 115200). Furthermore, how is this instance then initialized?

If we disable retarget, we see printf() in the debug terminal and NRF log in the debug UART. 
When enabling retarget so that printf also goes to the debug UART, we get the garbage data (also NRF LOG is no longer showing)

[Vidar Berg]

But instance 0 is used by the logger module. Could you not use the NRF_LOG_* macros instead of printfs then?

[newUser]

We started to use printf() because NRF_LOG_* did not print any text in the debug terminal.
To change all of printf in the source code takes a lot of time and has a huge impact on our source code.
This is why we prefer to reroute printf()

[Vidar Berg]

I see, but shouldn't it be quick and easy to replace the printf's with NRF_LOG_INFO or equivalent if you do a "search and replace" across your source files?

[newUser]

We have tried, but our Ubuntu colleague doesn't get any data to the debug terminal when using NRF_LOG_*. (RTT backend enabled and UART backend disabled in sdk_config).
For our Windows people, it works.

If we can get NRF_LOG_* to work on both Windows and Linux, we would like that very much. It would indeed solve all our problems.

Any ideas?

[Vidar Berg]

Does your Ubuntu colleague use an older version of Segger embedded studio by any chance? In that case, you may need to build with the 'NRF_FPRINTF_FLAG_AUTOMATIC_CR_ON_LF_ENABLED' setting disabled in sdk_config

Issue with RTT logs not being displayed in SES debug terminal: https://devzone.nordicsemi.com/f/nordic-q-a/45985/nrf_log-not-working-on-segger-embedded-studio/182742#182742