make: verify before flash

[kaspar030]

Contribution description

Some flashers (jlink) check if the flash contents already matches the to-be-written binary and if yes, skip re-programming. That saves time and flash cycles.

This PR adds make infrastructure to support that with other flashers, too.
Basically it works by, instead of doing $flash $flash_args, it does $flash_verify || $flash $flash_args.
If no FLASH_VERIFY is provided, false is used thus flashing is done as before.

Another commit implements this for edbg.

Testing procedure

With an edbg supported board, try make all; make flash-only; make flash-only and observe that the first flashing actually programs the device, the second skips programming.

Also test non-edbg boards (which don't yet supply "FLASH_VERIFY").

Issues/PRs references

none

[cladmi]

I like the idea, but I would define it empty by default and add the handling if defined.
Seeing false || ./openocd.sh firmware feels out of place.

Also, both variables need to be documented.

[jcarrano]

One observation: this works only if the flasher only flashes and nothing more. If the flasher also resets, then the reset has to be added as an additional step that is always performed.

[cladmi]

I tested, and with edbg it does not break incremental flashing like done in makefiles/boot/riotboot.mk. The file currently does not use flash-recipe but I updated it to test.

@jcarrano On edbg it resets the board on the check.

Both these case should be documented as requirements.

Another solution is to allow overwriting flash-recipe and currently overwrite it for edbg only.
I think would just need to replace the current recipe name by default-flash-recipe and do flash-recipe ?= default-flash-recipe. And then in edbg.inc.mk do flash-recipe = edbg-flash-recipe that defines the new behavior.

[maribu]

I fixed a typo in the PR description. (false || flash should is used when no verification command is present, not true || flash)

[jcarrano]

@jcarrano On edbg it resets the board on the check.

I don't think that's a problem. I'd even say it's better: after FLASH the board is reset, so having it reset after verify is consistent.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you want me to ignore this issue, please mark it with the "State: don't stale" label. Thank you for your contributions.

[maribu]

ACK. I'd love to see this merged. In a previous post @cladmi already confirmed that it works, so testing is already done.

I agree that more documentation would be nice. But honestly, this would require some dedicated section in Doxygen for the build system to add this to. This is however currently missing. (I think that such a section would be helpful to keep the use of the build system more consisted, as people will have some place to look at when trying to figure out how to add something to the build system. But that is out of scope of this PR anyway.)

[aabadie]

more documentation would be nice

@maribu, I think @cladmi suggestion was to add some documentation of the new variable in vars.inc.mk.

[kaspar030]

Closing in favor of #12301. Indeed @cladmi's suggestion is nicer (more localized).