Oh cool, so its more than /just/ graphics code, theres a whole load of stuff that they would need to implement?

I can see why they would want that to be their own - make the pi 100% open - but sounds like a mammoth task! (especially if its only 1 guy doing it?)

> need to implement

I think "need" implies too much. Because, for example, for 100% headless applications the open+free version is already viable. (But in practice everyone wants to debug using the HDMI from time to time, mostly because almost noone has NTSC lying around.)

Also, without looking at the docs of the VPU, I'd guess that most of the blob functionality is needed for advanced vector stuff and whatnot (so it's only needed if you want to implement OpenGL/EGL/WebGL).

Oh so if it’s just for ssh then you can boot without the raspi-firmware part?

Are there images without it?

No, you can't boot into ARM code without it. ARM part is disabled power-on, VPU is a general purpose processor really. Basically, on start-up it loads its start.elf (i.e. boot application compiled for its instruction set) from boot-media, initializes some hardware, then loads ARM boot image into common memory, then starts ARM. It also exposes some low-level hardware interface via syscall-type "mailbox" interface.

It looks like, per https://github.com/librerpi/lk-overlay#what-features-work , yes you can boot to Linux on a Pi 2 with composite video and ... it doesn't use the word headless anywhere, but I'd be very surprised if you can't just omit video outputs completely.

EDIT: Actually, reading more carefully it looks like there might be more than one blob and it's not 100% clear to me which this replaces, so now I'm less sure that you can boot without any proprietary blobs. I'm not sure that you can't, but I can't tell.

There’s also the serial console one could use

An annoying side effect is that the (closed) "core OS" that the Pi runs on, ThreadX, is owned since 2019 by... Microsoft !

https://en.wikipedia.org/wiki/ThreadX

https://ownyourbits.com/2019/02/02/whats-wrong-with-the-rasp...

Note that the above is specific for the Pi 3 - the Pi 4, for instance, doesn't have the issue of a ridiculously undersized power connector (2.5W minimum standard for up to 13 W demand !!)

Yeah, it's more than just graphics.

Here's an interesting blogpost that kinda explains the multiple boot stages: https://www.furkantokac.com/rpi3-fast-boot-less-than-2-secon...