build time with west for zephyr projects : how to re-build without the 'build setup' phase eg when just recompiling C files

[BrianW]

I'm building my zephyr project for nRF5340, using west.

However, each time I change my code and re-build to try it, my PC (which is pretty recent) takes around 40-50s just re-doing all the build config stuff, rebuilding the core zephyr bit etc before actually compiling the 1 or 2 C files I changed! This ends up being quite frustrating...

I already tell west the --pristine auto option, which does mean it only re-compiles the C I changed, but how can I get it to not redo all the build config stuff ( as generally I have no changes to CMakefiles, no changes to dts files etc)

thanks!

[dejans]

Hi,

Have you changed NCS version in the meantime or done any other change?

Is there a reason why you use --pristine instead of --pristine=auto as you did previously?

Best regards,
Dejan

[BrianW]

No changes to NCS versions. 

The main change is to using a specific board file that is in a 'local project' directory (hence I have to set BOARD_ROOT for the 'pristine' build)

As I said: 

BrianW said:

My 'incremental' build line is:

west build --build-dir cc1-med/build -S dev cc1-med --pristine=auto

but this now systematically rebuilds the makefiles/subimage.

Is there any known issue with using either snippets (-S) or a specific BOARD_ROOT for the pristine=auto option?

[dejans]

Hi,

What is the behavior when you use "west build" in following situations
1 using snippets without specific BOARD_ROOT
2. using specific BOARD_ROOT without snippets?

Best regards,
Dejan

[BrianW]

dejans said:

1 using snippets without specific BOARD_ROOT

build fails, as it can't find the board files for the board type "cc1medv1_nrf5340_cpuapp" (normal, they are n the specific BOARD_ROOT...)

dejans said:

2. using specific BOARD_ROOT without snippets?

Ok, this seems to correctly not rebuild everything...

I guess this means the incremental build system can't cope with snippets?

[dejans]

Hi,

If you look at the output of "west build --help" command, there is an explanation of "pristine builds" and the following statement "Setting --pristine=auto uses heuristics to guess if a pristine build may be necessary." I think what might be happening in your case is that heuristic's guess is wrong when using snippets which causes full rebuild. If you are not satisfied with how the heuristics behave, you could disable the heuristic by running "west config build.pristine never" as shown in the Tip of pristine builds. Additional information is available in the Configuration Options.

Best regards,
Dejan