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Unused ROM Anywhere?

Posted: Fri Apr 01, 2022 12:36 pm
by chysn
I know all (or most) of the nooks and crannies in RAM where I can put little machine language routines.

Are there any such "empty" places in ROM? Something that is never used, where ROM hackers can put something short? I don't much care if it's KERNAL or BASIC. I haven't seen anything promising in the disassembly, but I figured I might not recognize such a thing.

Re: Unused ROM Anywhere?

Posted: Fri Apr 01, 2022 12:50 pm
by tlr
Commonly enhanced kernals would strip out RS-232 routines and/or tape routines to allow space for added code.

Re: Unused ROM Anywhere?

Posted: Fri Apr 01, 2022 1:22 pm
by srowe
There's some empty patch space in both BASIC and the KERNAL
  • $DF52 - 40 bytes
  • $E47C - 37 bytes
  • $E4DA - 38 bytes
  • $FF85 - 5 bytes
  • $FFF6 - 4 bytes

Re: Unused ROM Anywhere?

Posted: Fri Apr 01, 2022 1:25 pm
by chysn
tlr wrote: Fri Apr 01, 2022 12:50 pm Commonly enhanced kernals would strip out RS-232 routines and/or tape routines to allow space for added code.
Thanks! It crossed my mind that RS-232 might be a good candidate for general uselessness.
srowe wrote: Fri Apr 01, 2022 1:22 pm There's some empty patch space in both BASIC and the KERNAL
Thanks! It doesn't seem like much, but a few dozen bytes here and there might be useful.

Re: Unused ROM Anywhere?

Posted: Fri Apr 01, 2022 2:15 pm
by Mike
srowe wrote:There's some empty patch space in both BASIC and the KERNAL
  • $DF52 - 40 bytes
  • [...]
This space already contains my patch for the bugged multiplication routine in the BASIC interpreter. :mrgreen: