
Pi-based BBC Micro Co-Processor - mmastrac
http://stardot.org.uk/forums/viewtopic.php?f=3&t=11325
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david-given
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](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...

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

[http://www.sprow.co.uk/bbc/armcopro.htm](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!

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mmastrac
The project's wiki might actually be a better link:
[https://github.com/hoglet67/PiTubeDirect/wiki](https://github.com/hoglet67/PiTubeDirect/wiki)

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krige
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?

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jacquesm
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.)

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72deluxe
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!!

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

~~~
72deluxe
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?

