From: Nicolas Welte; address is valid for replies (Re:) only! (welte_spam_at_freenet.de)
Date: 2003-02-02 16:05:45
I kept having a minor problem with my 6502 FlashROM board which led to a
system crash sometimes, especially when resetting the machine or when using
Marko's c2nload utility if the Flashmode on my hardware was enabled.
Now I think I found the reason, the following code in the VIC20 (PAL) KERNAL ROM:
.C:fd62 B1 C3 LDA ($C3),Y
.C:fd64 91 C3 STA ($C3),Y
.C:fd66 99 14 03 STA $0314,Y
This copies some vectors from ROM to RAM, but why does it contain an STA
command back to ROM? I think I'm going to patch this out with two NOPs, and
then the problem should be gone. For some reason the FlashROM locks up the
system even if it did not receive the magic sequence to enable the
programming mode. The only way to fix the problem is to avoid writes to the
Flash chip it seems.
Can anyone think of problems that I could create when I patch this code
fragment?
I'd also love to hear about patched versions of the VIC20 ROMs. Were there
any, except maybe the localized versions?
Nicolas
PS: I wrote a nice flash program for the floppy drive version of my hardware.
Look here: http://people.freenet.de/x1541/hardware/flash64.html
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