Hi, I know it isn't liked to use MMC5 for homebrew, but for the past year I've been making my game in it.
I am having a really hard time understanding how this works. I am quite sure I set up the IRQ wrong,
and I am even moreso worried about how the PCM is even supposed to be fed.
Here is my code, please keep in mind all of this is guess work, I don't even know how an IRQ runs.
The code to initiate the IRQ is also in the Main game loop and not in VBlank.
The game plays the sample but it is very noisy. The only thing that plays right is the volume, Everything else is a mess.
Here is a link to both PCM and original sample.
The sample is an 8-bit unsigned wav PCM 1000bytes approx
https://drive.google.com/drive/folders/ ... drive_link
Frequency spectrum of original sample
![Image]()
NES Sample
![Image]()
Here I'm showing that it appears that I am not able to set up the IRQ and sample feed loop well as the sampling happens
at horrible intervals
![Image]()
The green dots (At left) are IRQ activations. The teal dots everywhere are PCM $5011 writes.
Often on the frame after there are absolutely no IRQ activations at all. (Likely just my code)
![Image]()
This isn't a case of I've tried everything, but rather that I have no idea if I'm doing anything right.
My questions are.
1. How am I ->actually<- supposed to do the IRQ? The wiki says this
MMC5's DAC is changed either by writing a value to $5011 (in write mode) or reading a value from $8000-BFFF (in read mode). If you try to assign a value of $00, the DAC is not changed; an IRQ is generated instead. This could be used to read stream 8-bit PCM from ROM and terminate at $00.
And then this Psuedocode, which I honestly don't know how to translate or use practically2. Is my sample type correct?
I choose a wav of 8-bit PCM unsigned, (I also cut out the header in it)
3. How do I set the IRQ? Do I initialize it in Vblank? How often do I initialize it?
If anyone can help me, thank you so much. I don't have access to the only game that uses this Shin 4 Nin Uchi Mahjong.
But I definitely know people here have run the PCM just fine.
I am having a really hard time understanding how this works. I am quite sure I set up the IRQ wrong,
and I am even moreso worried about how the PCM is even supposed to be fed.
Here is my code, please keep in mind all of this is guess work, I don't even know how an IRQ runs.
The code to initiate the IRQ is also in the Main game loop and not in VBlank.
Code:
IRQ: STA $0400 STX $0401 STY $0402AcknowledgeIRQ: LDA $5204 ;Acknowledge IRQ LDA #$80 STA $5010 ;PCM IRQ Enable LDX #$20Repeat16: LDA [SampleIndex], y ;Index STA $5011 ;PCM Write INC SampleIndex DEX BNE Repeat16 ;16 cycle loopIncSampleIndex: LDA SampleIndex ;Increment Highbyte after 256 BNE IRQ2 INC SampleIndex+1 LDA SampleIndex+1 ;Loop Highbyte at $B000 CMP #$B0 BNE IRQ2 LDA #$A5 ;Return to $A500 STA SampleIndex+1 JMP IRQ2 ;Here just to show IRQScanlinecode closerIRQScanline: .db $10,$20,$30,$40,$50,$60,$70,$80,$90,$B0,$D0,$EFIRQ2: INC IRQScanlineUpdate LDY IRQScanlineUpdate CPY #$0E ;Loop after index to 0E BNE IRQ3 LDA #$00 STA IRQScanlineUpdateIRQ3: LDA IRQScanline, y STA $5203 ;IRQ Counter LDA #$80 STA $5204 ;Enable IRQ flag LDA $0400 LDX $0401 LDY $0402 RTIHere is a link to both PCM and original sample.
The sample is an 8-bit unsigned wav PCM 1000bytes approx
https://drive.google.com/drive/folders/ ... drive_link
Frequency spectrum of original sample
NES Sample
Here I'm showing that it appears that I am not able to set up the IRQ and sample feed loop well as the sampling happens
at horrible intervals
The green dots (At left) are IRQ activations. The teal dots everywhere are PCM $5011 writes.
Often on the frame after there are absolutely no IRQ activations at all. (Likely just my code)
This isn't a case of I've tried everything, but rather that I have no idea if I'm doing anything right.
My questions are.
1. How am I ->actually<- supposed to do the IRQ? The wiki says this
MMC5's DAC is changed either by writing a value to $5011 (in write mode) or reading a value from $8000-BFFF (in read mode). If you try to assign a value of $00, the DAC is not changed; an IRQ is generated instead. This could be used to read stream 8-bit PCM from ROM and terminate at $00.
And then this Psuedocode, which I honestly don't know how to translate or use practically
Code:
(On DAC write) if(value=0) irqTrip=1 else irqTrip=0(On $5010 write) irqEnable=value.bit7(On $5010 read) value.bit7=(irqTrip AND irqEnable) irqTrip=0Cart IRQ line=(irqTrip AND irqEnable)I choose a wav of 8-bit PCM unsigned, (I also cut out the header in it)
3. How do I set the IRQ? Do I initialize it in Vblank? How often do I initialize it?
If anyone can help me, thank you so much. I don't have access to the only game that uses this Shin 4 Nin Uchi Mahjong.
But I definitely know people here have run the PCM just fine.
Statistics: Posted by YogiGame — Wed Feb 14, 2024 7:47 am — Replies 5 — Views 176