efm32: add support for riotboot

[basilfx]

Contribution description

This PR adds support for riotboot for EFM32 and all boards.

RFC

There is still one part that needs discussion (and should move to a different PR). 8ea2d1d exposes a global define that can be used to skip certain parts of the bootloader, when building the bootloader.

I need that for several reasons:

• reducing the size of the bootloader (EFM32 cpu_init() does a lot more)
• skipping parts in cpu_init() that are not relevant during boot
  • configuring clock sources
    • example: I could have an updated firmware that uses another source/configuration
  • e.g. chip applying errata
    • example: there can be new (conflicting) EFM32 errata
  • configuring DC-DC parameters
    • example: I decide to update DC-DC parameters to make my board more efficient or stable
  • peripheral initialization

My goal is to boot as quick as possible to the actual firmware on the defaults, and then do proper initialization.

I don't know if there is a better way to detect if I'm building the firmware, and I am happy to adapt if there is a way.

Resolved by #12297.

Testing procedure

cd tests/riotboot && BOARD=ikea-tradfri make test should work (or other EFM32 board, e.g. SLTB001a).

Issues/PRs references

#8902 (comment)

[fjmolinas]

@cladmi might want to take a look at the BOOTLOADER define.

[aabadie]

Otherwise I confirm this is working on the Pearl Gecko board. Nice!

[basilfx]

@cladmi @aabadie I have rebased this PR.

@cladmi Do you have an opinion on this approach, or know a better way? Would like to have something like this merged.

[kaspar030]

8ea2d1d exposes a global define that can be used to skip certain parts of the bootloader, when building the bootloader.

I think that's alright. The bootloader cpu_init() just has to initialize what's needed in order to successfully execute the bootloader's kernel_init and jump to the actual image.

[kaspar030]

(bikeshadding) maybe call the define "RIOTBOOT"?

[fjmolinas]

I would keep the term BOOTLOADER or use RIOT_BOOTLOADER instead of RIOTBOOT. riotboot is associated with a module that any application can use so I think we should try and keep it [edit:semantically] separate from stuff only the bootloader needs.

[basilfx]

I don't care. I think that RIOT_BOOTLOADER reduces chances on a conflicting define.

I was planning to split this commit from this PR, so I'll change it over there!

[kaspar030]

Well, "RIOT_BOOTLOADER" is just an arbitrary but new name of RIOT's bootloader, "riotboot". Why a new name?

"BOOTLOADER" is quite general, but in this case, we only mean riotboot. Why imply that this means any more than riotboot?

For referencing whether the support code is available, "MODULE_RIOTBOOT" can already be used.

How can people not be of the opinion that "RIOTBOOT" is the right name for this define? 😉

[kaspar030]

I don't care. I think that RIOT_BOOTLOADER reduces chances on a conflicting define.

I do a little. Please keep BOOTLOADER over RIOT_BOOTLOADER if RIOTBOOT doesn't resonate.

[fjmolinas]

How can people not be of the opinion that "RIOTBOOT" is the right name for this define? wink

I would think something that isn't RIOTBOOT is better since this isn't necessarily a riotboot boot-loader issue, but for any bootloader, e.g: for a case where e.g. mcuboot or similar would be supported, I imagine this initialization would need to be skipped. But that could be changed if and when the need arises.

Well, "RIOT_BOOTLOADER" is just an arbitrary but new name of RIOT's bootloader, "riotboot". Why a new name?

Ok, you are right.

[basilfx]

I created #12297 to address the riotboot part. Will update this PR once that gets merged.

[basilfx]

Cherry-picked #12297 on top of this one so it can be tested. Will remove this if #12297 gets merged.

[basilfx]

I've update this PR now that #12297 got merged. I've also disabled most parts of board_init(). Especially on the sltb001a, this reduces the size by almost 2kiB.

Due to #12311, this doesn't work on the sltb001a directly, but it is not related to this PR. I've tested this on the stk3600, slstk3401a, slstk3402a and sltb001a (with changes).

[benpicco]

This is very straightforward.

Only adds definition for bootloader size and skips certain board init parts if RIOT is used as a bootloader.

[benpicco]

Another rebase is in order.

[basilfx]

Rebased.