Inside geoWrite – 5: Copy Protection
https://www.pagetable.com/?p=1449
#retrocomputing #commodore64 #c64 #geos
@pagetable Nice article. Thanks for this series.
I might have found a typo in this one by the way. In the article, you have a code snippet that says "bra showErrorAndExit". Isn't this meant to be "bne"?
@loke It's a "bra" in the original code. "bra" is a 65c02 instruction that does not exist on the 6502, but the GEOS headers come with a macro for "bra".
Here's the weird thing about it though: It resolves into
clv
bvc
So it's a relative jump, but it takes up 3 bytes and uses 5 cycles. A jmp would be 3 bytes and 3 cycles. All of GEOS and its apps is full of clv/bvc. :(
@pagetable @loke Please modify the macro so I can sleep at night.
@modrobert @loke The GEOS KERNAL defines the macro (and also uses it). You can change it in my reverse-engineered source: https://github.com/mist64/geos/blob/master/inc/geosmac.inc :)
@pagetable @loke JMP