Unable to see uart logging from nRF51822 with ST-Link v2 and openOCD

[GlenPickle]

I'm attempting to modify some open source software for an nRF51822 chip found here: https://github.com/reversebias/mitosis

In this code there are some debugging lines that use uart to print some things out. The lines that I am referring to are in this file: https://github.com/reversebias/mitosis/blob/master/mitosis-receiver-basic/main.c and they look like this:

            // debugging help, for printing keystates to a serial console
            /*
            for (uint8_t i = 0; i < 10; i++)
            {
                app_uart_put(data_buffer[i]);
            }
            printf(BYTE_TO_BINARY_PATTERN " " \
                   BYTE_TO_BINARY_PATTERN " " \
                   BYTE_TO_BINARY_PATTERN " " \
                   BYTE_TO_BINARY_PATTERN " " \
                   BYTE_TO_BINARY_PATTERN " " \
                   BYTE_TO_BINARY_PATTERN " " \
                   BYTE_TO_BINARY_PATTERN " " \
                   BYTE_TO_BINARY_PATTERN " " \
                   BYTE_TO_BINARY_PATTERN " " \
                   BYTE_TO_BINARY_PATTERN "\r\n", \
                   BYTE_TO_BINARY(data_buffer[0]), \
                   BYTE_TO_BINARY(data_buffer[1]), \
                   BYTE_TO_BINARY(data_buffer[2]), \
                   BYTE_TO_BINARY(data_buffer[3]), \
                   BYTE_TO_BINARY(data_buffer[4]), \
                   BYTE_TO_BINARY(data_buffer[5]), \
                   BYTE_TO_BINARY(data_buffer[6]), \
                   BYTE_TO_BINARY(data_buffer[7]), \
                   BYTE_TO_BINARY(data_buffer[8]), \
                   BYTE_TO_BINARY(data_buffer[9]));   
            nrf_delay_us(100);
            */

When I uncomment this code to try to read the keystates that are being logged, nothing appears in my console, but I've noticed that the firmware runs much more slowly.

When I do this, I'm connecting an ST-Link v2 to the 3.3V, GND, SWDIO and SWDCLK pins of the NRF51822. I am using openOCD to open a debugging session, which allows me to flash the firmware to the nRF51822. I have no problem getting a debug session with OpenOCD or flashing the firmware. When I ground the GPIOs that should trigger the debug logs however,  I don't see anything in the openOCD session.

Am I looking in the right place for these log statements?

Other details: I'm on Ubuntu 18.04 and using the nordic SDK11.

[Edvin]

Hello,

You can't see UART messages via openOCD. I suspect what you are looking for is RTT logging. Please check out this blog post.

Alternatively you can use a UART terminal (Putty or Termite) to watch the UART log.

I assume you aren't using an nRF51 DK, since you are using ST-Link? 

BR,

Edvin

[GlenPickle]

Thank you for the response! I have done some research into the RTT logging, but unless I'm understanding something incorrectly it seems I might need to buy some new debugging tools (like a JLink) to use that. 

I will experiment with trying to open a UART Terminal, thanks!

I am not using an NRF51 DK, I have the core nRF51822 module SMD soldered to my PCB.

[Edvin]

Ok. I see. What do you connect to SWDIO and SWDCLK to program your nRF51? 

UART should work either way, but note that you need something to translate from UART to "Simulated UART"(USB), so that you can use a terminal like Termite or Putty.

[GlenPickle]

Sorry for the delay. To connect to the SWDIO and SWDCLK to program the nRF51 I use an ST-Link v2. I'll look into some way to translate UART to USB so that I can open a putty session. A J link would be able to do that if I bought one right?

[Edvin]

Well. I am not sure, actually. The SEGGER chip does this.

A JLink will be able to use RTT logging. 

If you want an easy way to see UART logging, you can check out some of the devices from the pictures when googling "Uart USB cable".

But with a JLink, you should be able to see the RTT log using RTT Viewer. See this guide from my previous reply to see how to set it up.

[GlenPickle]

I never did end up figuring out how to read print statements, but I found a different solution. I only wanted to print things in order to debug the program, and gdb ended up being the best way to do that. OpenOCD automatically starts a gdb session when you use it, which allowed me to make progress in my project.