Hi folks!
I dunno if anyone's thought of this before, but over Xmas I came up with a
nifty way of using the break button safely. With a program sitting over
the ROM in section A, I was using the following code to return basic:
ORG 62h
back OUT (251),A ; Ensure XMEM bit is disabled
OUT (250),A ; Page ROM into section A.
nmi LD A,31
JR back
Now, this works fine, but the stream of nmis that gets sent by the button
usually fills up the nmi handler stack, which is nicely placed above the
page allocation table, thus corrupting it and making lots of nasty things
happen later on.
So, I decided to alter the code to pause for a bit before returning to
basic, and junking any return addresses generated by subsequent nmis,
avoiding any stack overflow:
ORG 62h
back OUT (251),A
OUT (250),A
nmi POP HL ; junk return address
LD BC,1000h
loop DJNZ loop
DEC C
JR NZ,loop
LD A,31
JR back
Hope this helps someone.
\\///
(o o)
+----------------ooO-(_)-Ooo----------------+
| Steve Taylor [EMAIL PROTECTED] |
| Pembroke College |
| Cambridge CB2 1RF |
+-------------------------------------------+
