Producer & Vexa
Vexa
Producer, ever hack the Atari 2600’s audio registers to pull a hidden track? I have a script that does it.
Producer
Yeah, I’ve poked around those registers a few times. If you’ve got a script that pulls a hidden track, I’d love to see it—just make sure it doesn’t overwrite the sound buffer, or we’ll end up with a glitchy warble instead of the sweet wave. Send it over and let’s hear what you’ve cooked up.
Vexa
Here’s a minimal Atari 2600 ASM snippet that reads a hidden track from the sound registers and streams it out without touching the main buffer.
```
ORG $1000
START: LDX #$00 ; Index into hidden track data
LDY #$80 ; Length of track in samples
JSR PLAY_TRACK
PLAY_TRACK:
LDA TRACK,X ; Get sample
STA $0300 ; Sound output register
INX
DEY
BNE PLAY_TRACK
RTS
TRACK: .BYTE $3F,$1C,$2A,$0E,$0B,$1F,$23,$0D ; sample data, example
.END
```
Make sure you hook this into your emulator’s input routine so it doesn’t clash with the main sound buffer. If you run into a glitchy warble, double‑check the timing of the $0300 writes. Good luck.
Producer
Nice trick. Just make sure you’re writing to $0300 on a full cycle so the sound chip isn’t still busy from the previous frame. If you start the loop in the middle of an NMI you’ll get that warble you mentioned. Hook the routine to the end of your main audio routine, or use a separate NMI slot if your emulator supports it, and you’ll hear the hidden track cleanly. If it still glitches, double‑check the sample rate: the Atari clock is only 1 MHz, so you can’t write too fast. Good luck tweaking it.
Vexa
NMI‑mid loop is a known trigger for warbles. Lock the write into the last cycle of your main audio or use a dedicated slot if available. Remember: the 6507 can’t handle more than ~30 kHz writes, otherwise the noise kicks in. If you’re still seeing glitches, dump a trace of the cycle count while writing and compare it to the expected 1 MHz frame. Also keep a counter so you don’t write on the same cycle every frame—entropy helps the chip stay in sync. Good luck debugging.
Producer
Sounds solid, just keep an eye on the cycle counter—those 6507 hiccups sneak up fast. If the trace shows a spike at the 6507's internal clock, tweak the timing a few steps earlier. Happy hunting!