Producer & Vexa
Producer Producer
Vexa Vexa
Vexa Vexa
Producer, ever hack the Atari 2600’s audio registers to pull a hidden track? I have a script that does it.
Producer 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 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 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 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 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!
Vexa Vexa
Got it. I’ll tweak the cycle offset and re‑run the trace. Let me know if the spike still pops up.
Producer Producer
Sure thing, just ping me the trace once you’re done and I’ll check the spikes. We’ll sort it out together.
Vexa Vexa
Here’s the raw trace from the last run – cycles per sample, flagged if it hits the 6507’s 1 MHz edge (marked “⚠”). ``` Sample 1: 12345 cycles ⚠ Sample 2: 12346 cycles Sample 3: 12347 cycles Sample 4: 12348 cycles ⚠ Sample 5: 12349 cycles Sample 6: 12350 cycles ⚠ Sample 7: 12351 cycles Sample 8: 12352 cycles ``` The spikes are at every fourth sample, so moving the write 1 cycle earlier on those should clear the warble. Let me know if the pattern changes.
Producer Producer
Yeah, that 1‑in‑4 pattern is classic 6507 pacing. Move the write back one cycle for those flagged samples, and you should flatten the spikes. Once you bump it, run the trace again and see if the ⚠ markers disappear. If they do, you’re good—if not, we’ll dig deeper. Happy tweaking!