Date : Mon, 18 Mar 1996 13:48:00 +0000 (GMT)
From : Tom Seddon <T.W.Seddon@...>
Subject: My emulator -- small problems
I'm currently working on my emulator's filing system, but I'm still
tinkering with the hardware emulation now and again. I've got some
problems, and I'd be really grateful for any help.
1. The BREAK key
Sometimes this doesn't work. The screen clears and there are a couple of
blobs, but you have to press BREAK to start again. Does the Break key work
OK all the time in Xbeeb/MacBeebEm? (I've never used these two) To their
respective authors: how do you handle the break key? I just do a
SEI:JMP(&FFFC), without resetting the hardware (since the reset routine
will do this for me). Is this wrong?
2. D57D
There is a bit of code at D57D (or something like that -- maybe D75D?)
that reads:
D57D: BCS D57D
Occasionally my emulator gets stuck here (eg in Planetoid, and sometimes
when pressing keys). Obviously I'm doing something wrong... but what? I
remember there was once a book which gave a commented disassembly of OS
1.20 -- does anyone have this book? If so, what does the code at this
location do? I'll try putting NOPs there tonight, but I'd quite like to
know what this routine does before doing anything nasty to it!
3. Auto-booting ROMs
The interface to the filing system in my emulator is through a ROM which
calls illegal opcodes. I've tried to get it auto-booting when (1) no keys
are pressed on BREAK or (2) 'D' is pressed on BREAK. As recommended in
the 'Advanced Disk User Guide' I check location &ED for the internal
keycode for 'D', or just zero (indicating that no key is pressed).
However this doesn't work -- what is going on? OSBYTE &81 doesn't work
either... nor does accessing &EC. I'm pretty sure the hardware side of
things is OK -- almost everything I've tried has worked fine -- and I've
no idea what the problem is here.
Any help gratefully received. Of course I'll probably take one look at
the source tonight and fix all three problems instantly... :-)
(For those that are interested: barring any major mishaps, my emulator
will probably be released mid-April, when I get back to university.)
--Tom
| ** Tom Seddon ** E-mail: T.W.Seddon@...
- . - www: http://www.ncl.ac.uk/~n5013784/
/|\
//|\\ If you help a friend in need, he's sure to remember you...
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