logging data through the second UART (DMA) on nrf52840

[Eyal_Gal]

Hi.
In nrf52840 is it possible to use in NRF_LOG the second UART (DMA based) ? 

I know i can define the TX pin in the SDK_CONFIG but can the NRF_LOG_BACKEND_UART work with UARTE1 ?

[Jørgen Holmefjord]

Hi,

The UART instance used by the logger is hardcoded in the source (components\libraries\log\src\nrf_log_backend_uart.c:48 in SDK 17.1.0). If you want to use the second UART instance, you need to modify this line to:

nrf_drv_uart_t m_uart = NRF_DRV_UART_INSTANCE(1);

Note that the logger backend uses the UART driver configuration, so you need to enable the second UART instance in your sdk_config.h file:

// <e> UART1_ENABLED - Enable UART1 instance
//==========================================================
#ifndef UART1_ENABLED
#define UART1_ENABLED 1
#endif

Best regards,
Jørgen

[Eyal_Gal]

Thanks! But i looked in the code , doesn't it rely on the interrupts ? as far as i know it's based on DMA and from what i recall works differently than interrupt based UART, for input AND output (like you need to define the output buffer).

[Jørgen Holmefjord]

Hi,

Both UART and UARTE peripherals are using interrupt, the main difference is that UARTE peripherals uses EasyDMA to get/put data from/to buffers in RAM without CPU, while with the UART peripheral the CPU needs to provide/get the data to/from the peripheral for each byte.

NRF_LOG library uses the nrf_drv_uart driver, which will handle the differences between the peripheral types for you. The driver is configured to use UARTE for instance 0 used by the logger in most examples.

Best regards,
Jørgen

[Eyal_Gal]

thanks for the detailed explenation.! will try it out!