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Posted: Thu Nov 18, 2010 11:55 am
by blargg
The code from the Wiki works fine for me (testing on a PAL NES at the moment). I do notice that your code plays a very quiet noise either way, maybe that's the problem.
Posted: Thu Nov 18, 2010 2:43 pm
by neilbaldwin
blargg wrote:The code from the Wiki works fine for me (testing on a PAL NES at the moment). I do notice that your code plays a very quiet noise either way, maybe that's the problem.
Odd. It plays full volume here. Definitely not a volume issue.
*shrugs* I'm baffled.
Posted: Thu Nov 18, 2010 4:54 pm
by blargg
Can you show the complete code that you're using? Maybe the error is elsewhere. I just verified it on an NTSC NES as well, with the code running at reset.
Posted: Thu Nov 18, 2010 5:08 pm
by neilbaldwin
Just stripped it all down to this;
Code: Select all
reset:
sei
ldx #$FF
txs
lda #$00
sta PPU0
sta PPU1
jsr init_APU
mainLoop:
jmp mainLoop
nmi: rti
irq: rti
init_APU:
lda #$00
sta $4015
ldx #$00
@a: lda @apu_regs,x
sta $4000,x
inx
cpx #$18
bne @a
lda #$0F
sta $4015
lda #%00111111
sta $400c
lda #$01
sta $400e
;sta $400f
rts
@apu_regs:
.BYTE $30,$08,$00,$00
.BYTE $30,$08,$00,$00
.BYTE $80,$00,$00,$00
.BYTE $30,$00,$00,$00
.BYTE $00,$00,$00,$00
.BYTE $00,$0F,$00,$40
Which produces no sound until you put the 'sta $400f' line back in.
Posted: Thu Nov 18, 2010 6:29 pm
by blargg
Here's the problem; your init_apu routine is different than the one on the wiki:
Code: Select all
init_apu:
lda #$00 ; should be $0F
sta $4015
I've added a note to the Wiki as to not altering the init routine in any way. Using the above was preventing the length counters from being loaded properly by the loop.
Posted: Fri Nov 19, 2010 1:48 am
by neilbaldwin
That's very odd.
I originally had the init routine from the wiki, verbatim, and I wasn't getting any noise output unless I wrote something to $400F at the time of writing the frequency register ($0E).
So then I added the lines to write $00 to $4015 before the loop and $0F after the loop, just clutching at straws really. It didn't seem to have any effect.
Now I've restored the init back to the wiki version, removed the extra write to $400f and it's now working.
*shrugs* Ghosts in the machine maybe....
Posted: Wed Nov 24, 2010 2:10 am
by MetalSlime
tokumaru wrote:
From what I've read so far, the
Nerdy Nights sound tutorial is pretty straightforward and tells exactly what you have to do to get things going without much trouble, along with simple register descriptions. Assuming it's accurate, I guess it's a really good intro to sound programming.
Thanks! I wrote those tutorials to help people learn how to program the APU. The tech docs are great but dense. A lot of new homebrewers were coming in and posting ROMs of their games in progress, but they were all silent. I had just figured the APU out so I wanted to help out.
BTW, if anyone wants to host or copy/paste the Nerdy Nights sound tutorials somewhere in the nesdev wiki, you have my blessing. The more accessible they are to nes homebrewers the better.