On Thu, 06 Jul 2000, Albert Beevendorp wrote:
> > MAP.COM Which will crash the 1024 kB MSX turbo R ;-)
>
> Huh? How standard is it then (either MAP.COM or the MSX turbo R)?
MAP.COM is a dirty hack to make ill-behaving programs work on those DOS2
machines that are able to read the mapper ports.
What MAP.COM does is replacing the DOS2 routine that reads the copy of the
value of a mapper port from RAM with IN instructions. As a result of this,
programs that do OUTs directly to the mapper (and thus bypass the DOS2
memory routines) will work, but only if the IN returns the right value.
Some simple steps that make sure your program runs on all MSXes:
- Use DOS2 memory routines if they are present.
- If DOS2 memory routines are not present, make your own routines, which
store the values written to the mapper ports. When you need the current
value of a mapper port, don't do an IN, but read the stored value from RAM
instead.
Bye,
Maarten
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