Backup and restore monitor zero page usage

[stefan-b-jakobsson]

Hi,

This takes a backup of zero page addresses used by the monitor and restores them on exit, partly solving issue #111.

It works fine if you exit the monitor with the .X command. It will not work if you reset the computer. I'm not sure this is a good idea - or good enough an implementation. Marking it as draft.

[mooinglemur]

I think this approach is fine.

[stefan-b-jakobsson]

OK, I have to verify that it actually works as advertised.

[mooinglemur]

@stefan-b-jakobsson

Giving this some further thought, perhaps we should instead just switch to using BASIC ZP

We can steal exactly 11 bytes from $D4-$DE, the first two of which are poker/linnum, used for several things including address parsing, and the other 9 tempst are for 3 temporary pointers to strings when doing BASIC string evaluation.

For the remaining single ZP address we need, we can reuse forpnt at $E5, and if we need one more, we can steal $E6 as well. I think we will need it as I want to allow setting the rom/ram banks separately rather than having one variable for both.

What do you think?

[stefan-b-jakobsson]

At first glance, it sounds great. As far as I remember it uses 12 bytes from the zero page.

[mooinglemur]

Superseded by #173