bring back `px4-rc.params` file to set user defined params

[bastianhjaeger]

px4-rc.params file can be used to set/override parameters.

It was removed in https://github.com/PX4/PX4-Autopilot/pull/24600 and discussed to bring it back.

Test coverage

• Simulation testing :heavy_check_mark:

[dakejahl]

I think we need to do a little bit more, how does this make it into the ROMFS? @alexcekay added something similar recently https://github.com/PX4/PX4-Autopilot/pull/25449

[bastianhjaeger]

The way it worked before (and should still) is, that we ensure the file px4-rc.params is present in the context and then gets applied.

[alexcekay]

There are still things missing to fully bing this back.

• Please have a look at https://github.com/PX4/PX4-Autopilot/pull/24600/files#diff-2a4aa749b0ac200cb520539a8171ae5f8dc353e08be7edd519e945a7e6e7422a
• The file ROMFS/px4fmu_common/init.d-posix/px4-rc.params needs to be created again
• It needs to be added back to the ROMFS in ROMFS/px4fmu_common/init.d-posix/CMakeLists.txt

[bastianhjaeger]

Thx. Done.

[dakejahl]

So you want to edit the px4-rc.params file directly? Your comment in the code seems to indicate you want to use something in your PATH?

#user defined params for instances can be in PATH

With your latest commit you've added the file in-tree. If you want to have something in-tree then I would use the dynamic init system

CONFIG_BOARD_ADDITIONAL_INIT="rc.additional"

[dakejahl]

For hardware targets we also have config.txt and extras.txt. Maybe we want to bring this into SITL as well? We should try to simplify and minimize the configuration options https://docs.px4.io/main/en/concept/system_startup.html#customizing-the-system-startup

[bastianhjaeger]

So you want to edit the px4-rc.params file directly? Your comment in the code seems to indicate you want to use something in your PATH?

#user defined params for instances can be in PATH

With your latest commit you've added the file in-tree. If you want to have something in-tree then I would use the dynamic init system

CONFIG_BOARD_ADDITIONAL_INIT="rc.additional"

The way we used it so far was to add some path to "PATH" and put a file there called px4-rc.params, which then will be applied by the RCS file with

#user defined params for instances can be in PATH
. px4-rc.params

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[bastianhjaeger]

I see. https://github.com/PX4/PX4-Autopilot/blob/main/ROMFS/px4fmu_common/init.d-posix/rcS#L14

So it's a posix-only thing. It would be nice to do this in a more obvious and generalized way.

Not sure what you want to say?

[dakejahl]

I see. https://github.com/PX4/PX4-Autopilot/blob/main/ROMFS/px4fmu_common/init.d-posix/rcS#L14 So it's a posix-only thing. It would be nice to do this in a more obvious and generalized way.

Not sure what you want to say?

I am saying this is an empty file without clear purpose that gets put into the PATH in a non-obvious way that is specific to posix. Any reason why config.txt or extras.txt aren't suitable? We should try to minimize the number of configuration knobs. https://docs.px4.io/main/en/concept/system_startup#customizing-the-system-startup