ChipMusic.org - NES APU Fades

Re: NES APU Fades

2018-12-03T23:15:55Z

You're exactly right though, that's what he needs to do :]
Look at this link and also this one, you can just

jsr wait_nmi

before each lda / sta pair you do to get up and running, though it's a bit ugly. But hey, it's a start!
Each VBL wait is approx. 1/60 s.

Re: NES APU Fades

2018-12-03T05:35:32Z

Orgia Mode wrote:

Ugh, interrupts are such a headache for me, but if anyone can help it is nitro. I will be keeping an eye on the progress of this.

It's not me in this case. I haven't coded for the NES at all, so I can only give general advice. GB is my console. I'd recommend asking for help in the NESdev forums or wait for one of the NES gurus to come around.

Re: NES APU Fades

2018-12-03T05:01:28Z

Ugh, interrupts are such a headache for me, but if anyone can help it is nitro. I will be keeping an eye on the progress of this.

Re: NES APU Fades

2018-12-03T04:19:22Z

All the writes happen within microseconds of each other, and only the last (or should I say current) write is in effect. You would need to write a sequencer which writes a new value (for example) every frame in the NMI interrupt handler. So you would need to store a variable somewhere, and maybe a list of volume values in ROM that you would be reading one by one and writing to $4000.

NES APU Fades

2018-12-03T03:23:34Z

Hello Everyone! I'm back with another NES sound related question.
Having scrapped getting sound from the NES via a .nsf file, I have been trying to hard-code some little ditties into the chip in assembly.
My current process is this: I am making separate sub-routines for each note/note length and then calling them in an order, to form a sort of song.
Right now, my code for the note D, with a fade out looks like this:

D3:
;pitch D3
lda #%11111001
sta $4002
lda #%10000010
sta $4003

;volume & pulse width
;fade out
;F-D-B-9-7-5-3-2-1-0
lda #%00111111
sta $4000
sta $4000
sta $4000
sta $4000
sta $4000
sta $4000
lda #%00111101
sta $4000
lda #%00111011
sta $4000
lda #%00111001
sta $4000
lda #%00110111
sta $4000
lda #%00110101
sta $4000
lda #%00110011
sta $4000
lda #%00110010
sta $4000
lda #%00110001
sta $4000

RTS

and to an extent, this works! the NES generating a D3 pitch. HOWEVER: the fade is not working as expected. What I expect to happen is for the note to hold at maximum volume for a moment, before going down in volume. what happens in actuality, is that the APU only seems to be reading (from what i can hear) the last write to $4000, meaning that i have a steady tone at volume 1, rather than a tone that decreases in volume. If anyone can help me troubleshoot this, that would be very helpful.

Note: I understand that the length can be changed via the highest 5 bits written to $4003, but I still would like to experiment with this method and get it to work.