Making a switchable ST-Link, Blackmagic and DAPLink device

[lbthomsen]

First of all - apologies for creating this issue, which isn't really an issue with Blackmagic probe, but you guys seems to be the only ones having sorted this out.

First of all - I am using my own hardware which is to all intents and purposes an ST-Link/V2-1 (the stm32f103cb version from Nucleo). ST-Link works flawlessly and can be updated.

When I am building blackmagic firmware as described here: https://stm32world.com/wiki/Black_Magic_Probe, flash with stlink-tool from your repo, that too work flawlessly.

On this page https://github.com/blackmagic-debug/blackmagic/blob/main/src/platforms/stlink/README.md it described that after a power on it will start in st-link bootloader mode and need stlink-tool to boot the blackmagic but that is NOT what I see. After flashing blackmagic of my own build - it will start up each and every time. I can force it into bootloader mode by running stlink-tool -p and then reflash st-link firmware. In short - it works exactly as it should (but not as described in your own documentation).

Now, this is where I might lose your interest but I have build daplink firmware which can be flashed with your stlink-tool and work with st-link bootloader. That one however, works exactly like you describe in above readme - it starts up in the bootloader and need stlink-tool to run every time it is powered on.

So, in short, I know that this is daplink related and you presumably couldn't care less, but it would appear that you have figured out the "trick" at some point and I would be grateful if someone (whoever made this work) could help out with some pointers.

Please ask for any extra info you want. I really would love a device could be switched between all 3 without having to hook up an external debug probe to do so.

[lbthomsen]

The DAPLink behavior is described here: https://github-wiki-see.page/m/ziutek/DAPLink/wiki/DAPLink-on-STLINK

[dragonmux]

On this page https://github.com/blackmagic-debug/blackmagic/blob/main/src/platforms/stlink/README.md it described that after a power on it will start in st-link bootloader mode and need stlink-tool to boot the blackmagic but that is NOT what I see. After flashing blackmagic of my own build - it will start up each and every time. I can force it into bootloader mode by running stlink-tool -p and then reflash st-link firmware. In short - it works exactly as it should (but not as described in your own documentation).

This would be because that documentation reflects the behaviour of the ST-Link v2 itself, the bootloader and firmware variant found in the v2-1 on the Nucleo boards boots directly to the BMD firmware as noted. The docs aren't wrong, just a touch incomplete about that. stlink-tool still works fine though and can be used to reload other firmware if, after you've applied power, you bump nRST once on the STM32F103 - their bootloader detects this and doesn't boot the firmware but instead the bootloader when this is done after POR.

[lbthomsen]

This would be because that documentation reflects the behaviour of the ST-Link v2 itself, the bootloader and firmware variant found in the v2-1 on the Nucleo boards boots directly to the BMD firmware as noted.

Well, what I am trying to figure out is why, after power on, with everything else being the same, with BlackMagic firmware it boots straight into that (from st-link's standard bootloader) but with DAPLink it stays in the bootloader until stlink-tool is executed.

I would think that the st-link bootloader executes first and then decides to either stay in bootloader mode OR run the firmware on the specific address. So, the real question is, how is that decision made and I hope to find that out.