17 May
2000
17 May
'00
7:04 p.m.
On May 17, 13:06, Vintage Computer GAWD! wrote:
into
On Wed, 17 May 2000, Pete Turnbull wrote:
> Yes, probably :-) Since you wouldn't need much code, and nothing on a
> standard Apple uses interrupts, you could go one further and make it a
> time-sliced system instead of a cooperative one, with a very simple
circuit
> (not much more than a 555 timer, though you might
want it on a card
with a
PROM to hold
the code).
I considered this. An easier way to do this is to copy the BASIC ROM RAM in the upper 16K bank of memory and then modify
the interpreter to
switch after the execution of each BASIC program line.
Depends on whether you prefer hardware to software, I guess :-) Modifying
BASIC in a language card also has the advantage that it only tries to
switch when it's actually executing BASIC (rather than some DOS routine or
something you've BRUN) but I suspect that after-every-line is too often --
you'd spend a lot of time (proportionately speaking) context switching.
And it would be irregular; a multi-statement line encompassing a loop will
take much longer than a simple statement.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York