Pi-based BBC Micro Co-Processor | Hacker News Reader

Pi-based BBC Micro Co-Processor

stardot.org.uk

83 pointsmmastrac10 comments

For background, in case anyone doesn't know (huh, I was just discussing this here last week)...

The BBC Micro Tube interface is a fast interface which allows a second, quite different computer to use the BBC Micro as an I/O processor. Acorn made several: the most popular was a 3MHz 6502, but there was also a Z80 model which ran CP/M, a NS32016 with 1MB RAM which ran a custom OS, the famous ARM1, etc.

The second processor communicates with the BBC Micro via RPC, and can make any system call. The BBC Micro provides graphics, filesystems (including hierarchical disk and network filesystems), printer, keyboard, etc, all in a completely portable fashion. (The BBC Micro operating system was really rather good.) This keeps load on the second processor down. No I/O interrupts, no need for drivers, no real need for an OS if you don't want one; the 6502 second processor had a 2kB ROM and everything else in the address space was user RAM.

It looks like what this is doing is bit-banging the BBC Micro Tube interface and emulating a 6502 in software, so it's pretending to be a classic 6502 second processor (rather faster than the original!).

Here's a different project:

http://www.stardot.org.uk/forums/viewtopic.php?f=44&t=8852

It's an FPGA-based second processor module which (if I read it correctly) can be programmed with a soft core to be a 6502, 68000, 6809, Z80, 32016 or PDP11 second processor. Some crazy person seems to have even ported BBC Basic to the PDP11...

...also, hey, look: you can buy a new ARM7 coprocessor!

http://www.sprow.co.uk/bbc/armcopro.htm

It runs a minimal RISC OS workalike, just enough to run BBC Basic V. All this for a mere £88!

The project's wiki might actually be a better link: https://github.com/hoglet67/PiTubeDirect/wiki

Okay, but what's the purpose of this? Is it merely proof of concept work? Are there software that could utilize a 100 MHz BBC Micro? Or is just something incredibly cool for BBC Micro fans?

Something cool for BBC Micro fans.

The Pi is being used to emulate a co-processor communicates via an interface available on the BBC Micro called "Tube". For more info: https://en.wikipedia.org/wiki/Tube_(BBC_Micro)

Well... I think that the 'beeb' was hands down the best machine ever to learn how to program on.

It would be nice to see a re-vamped version of it and the 'pi' has all the bits and pieces. Hopefully this is the prelude to something along those lines that no longer needs a bbc micro as an io front-end. (Though, it would seem that doing that right out of the gate would be simpler than to use the original bbc so probably this is to satisfy an itch.)

It's an excellent piece of work, and you could probably use similar techniques to create addons for other 8-bit systems, but overall it's probably not super-interesting for non-BBC Micro fans ;)

BBC games tend not to work with a coprocessor - but a lot of business/serious software probably would (not much use these days of course...), and you can always use it for programming.

I've got a 16MHz 6502 coprocessor for my BBC and it works well. The coprocessor system is quite well designed, so the coprocessor has basically nothing to do but run BASIC or whatever, and the main 2MHz CPU only gets used for I/O. I/O-heavy stuff can be a little bit quicker sometimes; calculations and stuff run about as much more quickly as you'd expect from the clock rate. (In fact, they're a little bit quicker than that - because the coprocessor doesn't have to handle I/O, timers, keyboard scanning, etc., all of which can bog down the main CPU a little.)

My dad has a second processor in his loft, along with every other BBC (but not the Master Compact) and Acorns after that, plus no Electron (who would have one of them??)

Happy days spent using those things. Running Elite with a second processor did hidden line removal!!

We have/had an Electron, why wouldn't someone have one? (Not arguing, just curious.)

Only because of the perceived poor value of it in comparison to Beebs on the market at the same time, I thought?

Was there a difference in the BASIC implementations or am I imagining that?

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