How to debug configuration issues?

[Torsten Robitzki]

Hi,

I have a concrete example, where I have no clue, as to why a given configuration is not working. In general, I wonder, how one is supposed to debug / investigate such, quite time consuming issues.

I want to add RTT logging to a MCUBoot bootloader. Here is the configuration, that according to the available documentation (https://docs.nordicsemi.com/bundle/ncs-2.7.99-cs2/page/nrf/test_and_optimize/logging.html) should work:

CONFIG_LOG=y
CONFIG_LOG_BACKEND_RTT=y

This results in this warning:

warning: LOG_BACKEND_RTT (defined at subsys/logging/backends/Kconfig.rtt:4) was assigned the value
'y' but got the value 'n'. Check these unsatisfied dependencies: USE_SEGGER_RTT (=n),
(!LOG_MODE_MINIMAL) (=n). See
http://docs.zephyrproject.org/latest/kconfig.html#CONFIG_LOG_BACKEND_RTT and/or look up
LOG_BACKEND_RTT in the menuconfig/guiconfig interface. The Application Development Primer, Setting
Configuration Values, and Kconfig - Tips and Best Practices sections of the manual might be helpful
too.

I think, I understand that warning and applying it to my configuration yields this:

CONFIG_LOG=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_MODE_MINIMAL=n

But still, this results in a warning, that `LOG_BACKEND_RTT` got the value `n`, even though, `LOG_MODE_MINIMAL` is set to y.

warning: LOG_BACKEND_RTT (defined at subsys/logging/backends/Kconfig.rtt:4) was assigned the value
'y' but got the value 'n'. Check these unsatisfied dependencies: (!LOG_MODE_MINIMAL) (=n). See
http://docs.zephyrproject.org/latest/kconfig.html#CONFIG_LOG_BACKEND_RTT and/or look up
LOG_BACKEND_RTT in the menuconfig/guiconfig interface. The Application Development Primer, Setting
Configuration Values, and Kconfig - Tips and Best Practices sections of the manual might be helpful
too.

Beside the question, whether this should work or not, how should we debug such issues to find working configurations? Obvious starting point, is probably the mentioned definition of `LOG_BACKEND_RTT`:

config LOG_BACKEND_RTT
	bool "Segger J-Link RTT backend"
	depends on USE_SEGGER_RTT
	default y if !SHELL_BACKEND_RTT
	select SEGGER_RTT_CUSTOM_LOCKING
	select LOG_OUTPUT

I don't even see a dependency on `LOG_MODE_MINIMAL` in that code. Is it possible to somehow capture the call to the configuration parser and add some switches for more verbosity here? Are there other strategies to debug such issues?

(Version, nrf-connect v2.7.99-cs2, Target: nRF5340)

[Amanda Hsieh]

Hi, 

See the description of CONFIG_LOG_BACKEND_RTT:

You can set CONFIG_LOG_MODE_IMMEDIATE=y and it would also disable CONFIG_LOG_MODE_MINIMAL. 

Check out my colleague's unofficial sample mcuboot_smp_uart_feat_rtt. 

Regards,
Amanda H.

[Torsten Robitzki]

Hu Amanda,

thank you very much for your answer. According to the cited documentation, this should then work  (LOG_BACKEND_RTT get the value y), right? :

CONFIG_LOG=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_LOG_FRONTEND_ONLY=n
CONFIG_LOG_MODE_MINIMAL=n

But it still does not accept the value `y` (same message, as above). Adding `CONFIG_LOG_MODE_IMMEDIATE=y` does the trick, but where would I be able to pick up that information? How did you managed to find that adding `CONFIG_LOG_MODE_IMMEDIATE=y` would solve this configuration problem?

[Amanda Hsieh]

You can check the .config under build/mcuboot/zephyr to confirm the value of CONFIG_LOG_MODE_MINIMAL. I found CONFIG_LOG_MODE_MINIMAL=n doesn't take effect in the .config, and then try CONFIG_LOG_MODE_IMMEDIATE. 

[Torsten Robitzki]

So, you were just guessing? :-)

[Amanda Hsieh]

I see there are three modes in <choice LOG_MODE: Mode>, and  `CONFIG_LOG_MODE_IMMEDIATE=y` is used in my colleague's example. so it's worth to try.