Date   : Sun, 14 Feb 2010 11:37:39 GMT
From   : jgh@... (jgh@...)
Subject: Subject: Re: 'BASIC 512K'

Rick Murray wrote:
> I wonder if the co-pro was a side effect of Acorn looking for a
> worthwhile RISC chip for their new range of processors?

It was. Acorn were looking for something to step from 8-bit 6502s
to a suitable 32-bit CPU. They approached Intel to see if they
could license the 80x86 core, but Intel were only interested in
selling physical chips.

The 32016 gave Acorn the experience that showed that short, fast
instructions and fast interupt response was what was important.
Some 32016 instructions are 12 bytes long, BBC BASIC on an 8MHz
32016 barely manages to perform as well as BBC BASIC on a 2MHz
6502.

The beauty of the Tube system was that it takes a very small bit of
hardware and firmware to throw together a system that lets you
experiment with a new CPU without having to build an entire system
- the system is already there in the host processor. Typically, you
only need about 1K of client code, a Tube ULA and a couple of glue
chips.

> > My PDP-11 emulator is written in BBC BASIC and runs BBC BASIC quite
> > nippily on the ARM-7 CoPro.
> 
> Pure BASIC, or with assembler?

Pure BASIC, with a snippet of assembler for background escape
checking. See http://mdfs.net/pdp11 Being in BASIC means it runs on
any platform - fairly zips along on a fast Windows machine ;)

I've started putting together an ARM version now the BASIC version
has allowed me to flatten the bugs in the implementation.

-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
The most perfect world is an imperfect world as the imperfections
give people a reason to strive to change it.