I'd like to use CA65 to assemble a 6502 ROM that needs to run on its own, i.e. no other kernal available. I would like my program to start at $C000. But this means I'll also need to put $00 $C0 into the reset vector at $FFFC. Is there a way to have CA65 pad my program with zeroes between the end of the program and the reset vector?
i.e. what I'd like to do is write something like
.org $C000
reset: ;; Some code from here
NOP
irq: ;; more code
NOP
.org $FFFC
;; What do I put here for padding?!?!
.addr reset
.addr irq
and get a .prg file which can directly be used as a continuous ROM area from $C000 all the way to $FFFF.
I guess one thing I could do would be to write
.repeat 123
.byte 0
.endrepeat
but that would mean having to update that number every time I change my program.
Turns out the CC65 wiki has a page on .ORG that, while trying to dissuade me from doing this, also shows a neat solution using .res and some PC arithmetic:
.org $C000
reset: ;; Some code from here
NOP
irq: ;; more code
NOP
.res $FFFC-*
.org $FFFC
.addr reset
.addr irq