How to configure Zephyr for RTT logging with nRF5340?

[Jaewook]

So far, since UART has been working well, now, we are switching from UART to RTT to remove UART port connection from our PCB design. 

However, the output to RTT is working well but nRF53 couldn't receive any characters over RTT.

Is there any way to enable RTT input to receive characters through RTT

The prj.conf setup:

# Enable RTT to replace UART
CONFIG_STDOUT_CONSOLE=y
CONFIG_UART_CONSOLE=n
CONFIG_USE_SEGGER_RTT=y
CONFIG_SHELL_BACKEND_RTT=y

The output from the device (nRF53400) was properly print out in RTT View as shown below.

< Capture of RTT Viewer >

 

The environment : 

• Development board PCA10095 – nRF5340
• Segger J-Link – JTAG debugger.
• Host RTT software - J-Link RTT Viewer V7.20a
• OS - Linux Ubuntu-18
• Zephyr V2.5.0

The references I referred :

Links

devzone.nordicsemi.com/.../how-to-setup-zephyr-for-rtt-logging-with-nrf9160

devzone.nordicsemi.com/.../can-i-use-rtt-instead-of-uart-for-a-console-on-nrf5340

Thanks,

Jae

[Jaewook]

From my end, as I narrowed down this issue, I guess, it may be related with the blocking mode in z_shell_log_backend_enable function.

If I commented out the line (err = shell->iface->api->enable(shell->iface, true);) shown in the picture, the input to RTT was working well.   However, I am not sure about what the line means.  Does anyone know about this line or the blocking mode? Or, do you know any other proper way not to use blocking mode?  Please feel free to comment it.

Thanks,

Jae

[Jaewook]

To properly disable the CONFIG_LOG_IMMEDIATE, I found that you may set CONFIG_LOG_MODE_IMMEDIATE=n to disable.  Since the LOG mode should be related to system performance, so you may need to carefully decide it whether it can be disabled or not.   Still, I am not sure why this mode (CONFIG_LOG_IMMEDIATE) disables the input to RTT as disabling the timer of the input polling function.  

https://docs.zephyrproject.org/latest/reference/kconfig/CONFIG_LOG_MODE_IMMEDIATE.html#cmdoption-arg-CONFIG_LOG_MODE_IMMEDIATE

Thanks.

[Susheel Nuguru]

Hi Bae,

I took the fresh BLE peripheral_lbs example and changed the below configs 

CONFIG_LOG_MINIMAL=n
CONFIG_RTT_CONSOLE=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_LONG_BACKEND_UART=n

And i can see the logs on RTT as below on nRF53

[Jaewook]

Thank you for the testing!.   Yes, the output to RTT was not the issue to me either.

You may want to check the input to RTT to see if working.  If not working, you may check CONFIG_LOG_MODE_IMMEDIATE to see if disabled.

Now, with CONFIG_LOG_MODE_IMMEDIATE=n, both the output and the input worked well.

The only curiosity is why CONFIG_LOG_MODE_IMMEDIATE=y set the blocking mode to disable RTT input polling feature. So, regardless of performance concern, RTT input was not functional anymore with CONFIG_LOG_MODE_IMMEDIATE=y.

Thanks,

Jae