Date   : Mon, 18 Jul 1994 03:17:04 +0100
From   : jfid@... (James Fidell)
Subject: Re: benchmarks

Chris Rae wrote:

> On Sun, 17 Jul 1994, James Fidell wrote:
> > It strikes me that we would probably find a set of benchmarks useful
> > for profiling emulators, for comparing them with each other and for
> > comparing them with the real thing.
> 
> I'm not sure that I'm right in this but hang on a tick - aren't you the 
> only one who's got one working James?  ;-)

I was under the impression that there were a couple which were at
least as far advanced as mine, but I may have got the wrong end of
the stick, of course...

> On a similar note - how much more than just the 6502 instruction set do I 
> have to emulate to get BBC BASIC running? I'm going to jump for joy when 
> I finally see the ">" I've missed for so long but I'd like to have a 
> rough idea of when it's going to happen!

It depends somewhat on how you're emulating the keyboard etc., but you
probably need to get some of the system VIA done, bits of the CRTC and
video ULA and ignore the reset of memory-mapped IO.  If you want to
see the prompt, you're obviously going to have to implement some
sort of screen IO too.

You'll also need to deal with the paged ROM select switch.

The way I started was to trap all reads and writes to memory-mapped
IO, just implementing those that the OS accesses.

[ As an afterthought, the reason you need some sort of keyboard emulation
is because the OS scans the keyboard for pressed keys (eg, shift and ctrl)
and also the power-up option DIP switches.  If you get these wrong, weird
things can start happening when you're implementation is otherwise OK.

James.

-- 
 "Yield to temptation --             |
  it may not pass your way again"    |     jfid@...        
                                     |
        - Lazarus Long               |              James Fidell