FrankenBeeb

for bbc micro/electron hardware, peripherals & programming issues (NOT emulators!)
crj
Posts: 315
Joined: Thu May 02, 2013 4:58 pm

FrankenBeeb

Postby crj » Thu Nov 30, 2017 7:17 pm

Has anyone ever tried replacing the CPU in a Beeb with an ARM, some RAM and some ROM?

I have in mind then running a strange hybrid OS which is basically RISC OS, but emulates 6502 code when required, using the Acorn MOS for some bits of IO, running languages and filesystems from sideways ROM (or emulated sideways ROMs), etc. It feels like it would be possible to borrow a lot of techniques from from Springboard, !65Host and !65Tube.

It would also be possible to assist with a smidgen of custom hardware. The first thing which occurs to me is a specialised memory controller which, as well as all the usual stuff, can:
  • Present a region of bytes in physical memory as a series of 64-bit words in virtual memory, each encoding something like ADR PC,next_instruction : ADD PC,r4,#___<<n, providing efficient dispatch for emulated 6502 instructions
  • Present BBC Micro screen memory re-ordered as VIDC screen memory

I'm sure this is a terrible idea in practice, a vast sink for time and effort, but it does intrigue me rather...

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fordp
Posts: 919
Joined: Sun Feb 12, 2012 9:08 pm
Location: Kent, England

Re: FrankenBeeb

Postby fordp » Thu Nov 30, 2017 7:37 pm

Does sound a bit weird but I had similar ideas of converting all of the 6502 code over to C compiled for an ARM, in particular to allow the PiCopro to really fly. The idea of running a 6502 emulator too is a good one. I must admit I have a queue of projects that I would rather work on first but one of them that I will keep quiet about could be useful for this project.
FordP (Simon Ellwood)
Time is an illusion. Lunchtime, doubly so!

crj
Posts: 315
Joined: Thu May 02, 2013 4:58 pm

Re: FrankenBeeb

Postby crj » Thu Nov 30, 2017 11:21 pm

Actually, combining an Amber core and a 6502 in an FPGA could be even more fun, especially if one exposed the 6502 as an ARM coprocessor so it was easy for the ARM to manipulate the 6502's registers. It would be hilarious to have instructions like "MR6 r5,X" cropping up. (-8

northernbob
Posts: 42
Joined: Fri Nov 24, 2017 6:49 am

Re: FrankenBeeb

Postby northernbob » Tue Dec 05, 2017 9:02 am

crj wrote:Actually, combining an Amber core and a 6502 in an FPGA could be even more fun, especially if one exposed the 6502 as an ARM coprocessor so it was easy for the ARM to manipulate the 6502's registers. It would be hilarious to have instructions like "MR6 r5,X" cropping up. (-8


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