Access to UART with DMA under example "freertos_coap_server" SDK nRF52840-DK

[alex]

Good day!
Tell me how you can configure access to UART with DMA in the example freertos_coap_server for receiving and transmitting arbitrary messages. Also, please clarify what maximum write read buffer is available in DMA for UART?

Thank's

[Hung Bui]

Hi Alexander, 

As long as you don't use UART in blocking mode, but in interrupt mode it should work fine with the freertos_coap_server. We provided the app_uart_fifo library that you can use. Please have a look at the peripheral\uart example in the SDK as the reference. 
The maximum read/write buffer with DMA is defined by the MAXCNT register and it's upto 65kB. In the code it's defined by UART_RX_BUF_SIZE and UART_TX_BUF_SIZE

[alex]

Can you show how you can combine the "peripheral\uart example" you specified with "freertos_coap_server"

[Hung Bui]

Hi Alexander, 

Which issue do you have ? 
You would need to add all the drivers and libraries as showed in the uart example into the freertos example. In addition please add the configuration to sdk_config.h as showed in the example. 

One notice is that OpenThread is compiled with UART0 reserved for CLI (command line interface). If you are using nRF52840 you can use the UART1 instead. If you want to use UART0 for your application, you would need to recompile OpenThread. 

[alex]

Hung Bui said:

In addition please add the configuration to sdk_config.h as showed in the example. 

Need to add all the definitions from this file?

[alex]

How to recompile the OpenThread?

[Hung Bui]

You are right, you need to add the configuration definition from the sdk_config.h 

You can re-build the open thread library here: https://openthread.io/guides/build

But it would take some time to install the toolchain and build environment. If you just want to test UART, I would suggest to use UART1