No UART output from Printf()

[RodWatt]

Hi,

I am using an nRF52840 Dongle with an external debugger and an external UART, provided by a USB to UART adapter, its an FTDI board.

I have modified my overlay file, as below to enable the UART which is connected to the FTDI adapter..

&uart0 {
  compatible = "nordic,nrf-uarte";
  current-speed = <115200>;
  status = "okay";
  tx-pin = <29>;
  rx-pin = <31>;
};

I am using the standard Hello_World sample.

#include <zephyr.h>
#include <sys/printk.h>

void main(void)
{
	printk("Hello World! %s\n", CONFIG_BOARD);
}

This did not provide any output. 

I enable the shell in the prj.conf as below.

CONFIG_SHELL=y

This provides an output to the terminal, allowing data to be sent and received.

but Im still not seeing the "Hello World output from printk.

Rod

PS I am able to build and flash blinky so am confident with my tool chain and flashing is working as expected.

[Martin Lesund]

Hi Rod,

I think the issue is that you have not enabled flow control.

Please enable that in prj.conf.

[RodWatt]

Hi Martin,

I don't think thats it. I have used this before without flow control to save on the pin count.

Rod

[Martin Lesund]

I do not think that you should need to enable "shell" when running this sample.
Printk will print out on the CONSOLE which is default enabled when running on the Dongle. 

So the only thing you should do is to run the sample unmodified with .overlay file to change the UART pins

[RodWatt]

Hi Martin,

Initially I did not have the shell enabled and was just running the Hello World sample as normal. I only enabled the shell command to prove that I have set up the UART correctly and that the adapter was working. 

Rod

[Martin Lesund]

Hi Rod,
Do you see any difference in behavior if you use:

 compatible = "nordic,nrf-uart"; 

[RodWatt]

Hi Martin,

Unfortunately I have managed to brick it, so I cant try it. I have opened a separate ticket here

https://devzone.nordicsemi.com/f/nordic-q-a/64921/nrf52840-dongle-bricked-after-programming

Rod

[RodWatt]

Hi Martin,

No, it doesn't seem to make any difference.

My overlay file is as follows

&uart0 {
//  compatible = "nordic,nrf-uarte";
  compatible = "nordic,nrf-uart"; 
  status = "okay";  
  current-speed = <115200>;
  tx-pin = <29>;
  rx-pin = <31>;
//  rts-pin = <22>;
//  cts-pin = <17>;
};

and my prj.conf file is

CONFIG_STDOUT_CONSOLE=y
CONFIG_SHELL=y

I see this

with CONFIG_SHELL=y not set, its a black screen

[RodWatt]

Hi Martin,

I got this working by adding the following line to the prj.conf f.le.

CONFIG_UART_CONSOLE=y

Im now seeing the printf() as expected.

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