Date   : Fri, 26 Jan 1996 13:59:03 +0000 (GMT)
From   : Tom Seddon <T.W.Seddon@...>
Subject: Re: Would this work?

On Fri, 26 Jan 1996 jkb@... wrote:

> Steven Flintham wrote:
> 
> [...]
> >jump to the language entry point. Instead of making the emulation good
> >enough to run the BBC OS, I would trap all jumps to code above &BFFF
> >and implement the operating system routines required (e.g. OSWRCH,
> >OSFILE etc) in C. Would this be sufficient to get BASIC working
> >properly?
> 
> No. The OS is more than a collection of OSWRCH type calls. However
you don't
  ^^
!!!

I have written an emulator which worked in the way he described. It worked
fine! However it was on the Atari ST so it was rather slow (~40-50% BBC
speed). The way I did it (a very bad way really...) was to trap each
JSR/JMP, and if the address was >&FB00 I checked the address against a
table... (oh dear... it's all coming back now... this is really
embarrassing) and if the entry was in the table then it performed the
appropriate routine... it was very slow.  (The first version didn't check
the jump address to see if it was >&FB00, and wow! that was slooow!)

Anyway, you get the idea. It was REALLY bad, but it DID work. I 
eventually got as far as having a small selection of * commands and some 
OSFILE support (so loading and saving BASIC programs did work).

--Tom

     .                     ** Tom Seddon **                     .
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