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Paulko64
Registered: Jul 2010
Posts: 24 |
How to correctly use KERNAL routines from a cartridge?
Hi there,
The last couple of days I've been struggling heavily to get the Kernal SCNKEY routine to work correctly when called from a cartridge build. I think I maybe missed something crucial in the memory init or something, but I can't figure out what I'm doing wrong. Perhaps somebody here can help me.
My cartridge starts with:
.word launcher
.word launcher
.byte $c3 ;c
.byte $c2 ;b
.byte $cd ;m
.byte $38 ;8
.byte $30 ;0
launcher sei
cld
ldx #$ff
txs
jsr $ff84 ;init I/O
ldx #$17
lda #$00
lp1 sta $d400,x ;clear SID registers
dex
bpl lp1
tay ;(A still contains zero)
lp2 sta $0002,y
sta $0200,y
sta $0300,y ;clear a bunch of low-memory locations
iny
bne lp2
tax
ldy #$a0
jsr $fd8c ;init system constants (without the ram-test)
jsr $ff8a ;restore kernal vectors
jsr $ff81 ;init screen editor
cli
ldx #$fb
txs
Then I copy all my code to RAM, disable the cartridge, and start my game from RAM. The above is enough to get my game running. However, when I try to access the kernal with the following part, it does not register any keys pressed:
lda #%00110110 ;enable kernal
sta $01
jsr SCNKEY ;read keyboard
lda #%00110101 ;disable kernal
sta $01
It should put the current key pressed in $0277, but there is nothing there. When starting the SAME build from the prompt, i.e. without copying first from cartridge it works correctly!
I already checked that all relevant ZP and $02XX adresses are set correctly. So I'm kind of lost here, maybe someone has some ideas?
Thanks,
Paul |
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Pex Mahoney Tufvesson
Registered: Sep 2003
Posts: 54 |
Your slideshow is awesome, simply awesome! Congratulations on a world's first in 2013! This is one for the history books! :-D
---
Have a noise night!
http://mahoney.c64.org |
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tlr
Registered: Sep 2003
Posts: 1814 |
Hehe, thanks! :)
I'm sure something more radical could be done with similar techniques. |
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Zyron
Registered: Jan 2002
Posts: 2381 |
So much new amazing things still happening in the world of c64 coding it's insane! |
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Mr. SID
Registered: Jan 2003
Posts: 425 |
Awesome idea! |
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tlr
Registered: Sep 2003
Posts: 1814 |
@mahoney: Perhaps you should try to define your original rules a bit more stringenly?
It would be fun to try to do something more flexible. :)
Your original rules aren't too bad as is actually. Executing BASIC code is actually implicitly disallowed via the code execution restriction because it relies on executing CHRGET/CHRGOT at $0073 in zp.
The main thing that is unclear is what piece of RAM you may modify.
You could say $0000-$0400 but that is a bit harsh restriction on e.g screen mem.
You could say that ROM, e.g $ffd2, may modify RAM outside $0000-$0400 but that is kind of pointless because all code executed is ROM code.
How about allowing read/write to all RAM?
If the $0000-$0400 RAM write restriction is to be kept, can the initial LOAD still load any amount of RAM? |
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