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Dr. Jay
Account closed
Registered: Jan 2003
Posts: 32 |
PAL/NTSC detect
Just wanted to share a quick routine that detects PAL/NTSC WITHOUT using interrupts or latches.
;pal/NTSC detect - 0 = PAL, non-zero = NTSC
palntsc
sei ; disable interrupts
wait
lda $d012
bne wait ; wait for rasterline 0 or 256
wait1
lda $d011 ; Is rasterbeam in the area
bpl wait1 ; 0-255? if yes, wait
wait2
ldy #$00
synch1 lda $d012
cmp #$37 ; top PAL rasterline
bne synch1
lda $d012 ; if next is 0, then PAL
synch2 cmp $d012
beq synch2
lda $d012
cli ; enable interrupts
rts ; return
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TNT
Account closed
Registered: Oct 2004
Posts: 189 |
WTF happened to my post above? Well, tlr pointed out the need for extra check.
Can anyone find something wrong with this approach:
.w ldx $d012
cpx $d012
beq *-3
lda $d012
bne .w
inx
beq .w
cpx #20
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tlr
Registered: Sep 2003
Posts: 1787 |
Quote: WTF happened to my post above? Well, tlr pointed out the need for extra check.
Can anyone find something wrong with this approach:
.w ldx $d012
cpx $d012
beq *-3
lda $d012
bne .w
inx
beq .w
cpx #20
Nice approach using just $d012 to avoid the race condition!
I think that will work. |
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j0x
Registered: Mar 2004
Posts: 215 |
l1 lda $d012
l2 cmp $d012
beq l2
bmi l1
cmp #$20
bcc ntsc
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tlr
Registered: Sep 2003
Posts: 1787 |
Quote:
l1 lda $d012
l2 cmp $d012
beq l2
bmi l1
cmp #$20
bcc ntsc
12 bytes. Very impressive!
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Devia
Registered: Oct 2004
Posts: 401 |
Quote:
l1 lda $d012
l2 cmp $d012
beq l2
bmi l1
cmp #$20
bcc ntsc
That's brilliant.
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Frantic
Registered: Mar 2003
Posts: 1647 |
I put it on codebase:
http://codebase64.org/doku.php?id=base:detect_pal_ntsc
I also wonder... does Ninja's older routine have any benefits over and above this short 12 byte routine? (Didn't have any time/energy to look into it myself now, sorry.) If not, I guess it could just as well be removed.
//FTC |
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Devia
Registered: Oct 2004
Posts: 401 |
You still need to catch NMI and disable IRQ for it to be completely reliable - and the 12 bytes is without the bcc in the end, which may be obsolete depending on how you implement it.
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Ninja
Registered: Jan 2002
Posts: 411 |
Frantic:
Technically, my routine does not have an advantage. From an educational point of view, it has (it was supplement code to an article after all) :) If you don't know the topic, then it surely helps to read my routine first, before you use the other (probably with disabling interrupts there, too). |
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Frantic
Registered: Mar 2003
Posts: 1647 |
Okok... Thanks for the information. In fact, I added the whole article to the page, since I guess it might add something of value to someone out there. (Just tell me if you mind...) |
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Kickback
Registered: Apr 2004
Posts: 97 |
Actually this helps me BIGTIME. Because I always thought that the PAL/NTSC register was the way to go.
Thanks guys for the information, helps me with NTSc/PAL intros ;-)
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