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Re: bedrock platform

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Theo <theom+news@chiark.greenend.org.uk> wrote:
> Computer Nerd Kev <not@telling.you.invalid> wrote:
>> Ben Collver <bencollver@tilde.pink> wrote:
>> > On 2026-05-08, Computer Nerd Kev <not@telling.you.invalid> wrote:
>> >> FreeDOS itself relies on the PC BIOS for hardware interactions,
>> >> instead of having its own chipset-specific drivers. Even if DOS is
>> >> running in an emulator on top of an OS such as Linux which can use
>> >> its own specific hardware drivers (if those exist for the specific
>> >> chipset used, which often requires that the chip manufacturer wrote
>> >> the Linux driver themselves), you still need the BIOS to initialise
>> >> the hardware first and boot that OS. The BIOS is therefore an
>> >> "external resource" required by FreeDOS, and unless an open-source
>> >> replacement such as Coreboot has been installed, it's got the same
>> >> "copyright issues" the author is proposing to avoid.
>> > 
>> > You can install FreeDOS in DOSBox or qemu, which both provide BIOS.
>> > That's how HP ships FreeDOS on UEFI-only laptops.
>> 
>> And you could run an emulator for a Raspberry Pi just the same, yet
>> the author rules that platform out.
> 
> The problem is that such an emulator doesn't exist.
> 
> Many RPi 'emulators' are just emulating a generic Arm target that runs RPi
> userland, without running the RPi-specific kernel.  QEMU does have some RPi
> targets, on which you can run the correct kernel, but they just implement
> a few of the API calls made to the Pi's GPU firmware, only the few that are
> needed to boot Linux.  
> 
> None emulate the GPU itself, which means that software that tries to talk to
> the GPU hardware won't work.

I don't know why. The QEMU website says the RPi framebuffer is
supported, and the operation of writing to it is in the "mailbox"
documentation that's been released for the Videocore IV RPis, so
one shouldn't need to reverse-engineer the GPU hardware/firmware
for that any more than for emulating DOS software running on a PC
with a proprietary graphics card.

A quick search found this bare-metal Raspberry Pi 3 framebuffer
animation which claims to work in QEMU as well as on real hardware:

https://github.com/Naevier/VideoCore-FrameBuffer

>  Perhaps that isn't such a problem, if you have
> part of your driver stack able to run GPU ops on the CPU instead.

Like with the PC, the "GPU ops" only get complicated if the
software uses the acceleration features of the GPU. I guess DOSbox
is probably more capable than RPi emulators there, but since you
can choose to write software that just uses the unaccelerated
framebuffer on the RPi, I still don't see why the platform gets
ruled entirely out while PCs are considered valid options.

> But that is not the point of a 'bedrock platform' - it's fully hardware
> emulated so that software can run identically, it doesn't depend on
> switching bits of your software stack for others.

You're not likely to _fully_ emulate all the hardware on common PCs
either, but you can emulate enough of either PC or RPi to allow
writing software that will work in all real or emulated
environments.

I'm not sure if either hardware platform avoids the author's issue
with proprietary firmware when using real hardware though. Both
seem the same to me in that regard.

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bedrock platform Ben Collver <bencollver@tilde.pink> - 2026-05-08 13:38 +0000
  Re: bedrock platform Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-05-08 21:03 +0000
    Re: bedrock platform kludge@panix.com (Scott Dorsey) - 2026-05-09 09:36 -0400
      Re: bedrock platform Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-05-09 23:30 +0000
  Re: bedrock platform not@telling.you.invalid (Computer Nerd Kev) - 2026-05-09 09:42 +1000
    Re: bedrock platform Ben Collver <bencollver@tilde.pink> - 2026-05-09 13:29 +0000
      Re: bedrock platform not@telling.you.invalid (Computer Nerd Kev) - 2026-05-10 08:44 +1000
        Re: bedrock platform Theo <theom+news@chiark.greenend.org.uk> - 2026-05-10 12:58 +0100
          Re: bedrock platform not@telling.you.invalid (Computer Nerd Kev) - 2026-05-11 09:15 +1000
          Re: bedrock platform Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-05-11 00:22 +0000

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