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+--- Thread: 4000 vs 4001 (/showthread.php?tid=5493)
4000 vs 4001 - KanedaFr - 07-04-2025
While looking for information about sound on NGP, I read two different explanations about the use of ports 0x4000 and 0x4001.
4000 is the noise channel setup port
4001 is tone channel 1 to 3 setup port
vs
4000 is the right channel setup port (noise, 1 to 3)
4001 is the left channel setup port (noise, 1 to 3)
Which one is correct? the last one, to allow stereo ?
RE: 4000 vs 4001 - KanedaFr - 07-17-2025
Is there any available doc about the sound part ?
The more I dig, the more I found it's not like explained.
For exemple, I found on the BIOS (0x3384) that you CAN directly write to the PSG registers from the CPU.
It's not mandatory to use a Z80 subcode to do so....
Of course, it's slower and wastes ticks but I found nothing about it for now
RE: 4000 vs 4001 - sodthor - 07-17-2025
Most sound dev/discovery by mic_ and his vgm player: http://jiggawatt.org/badc0de/console.htm (and related threads in this forum)
Maybe he can help you
and lately by winteriscoming: https://github.com/winteriscomingpinball/vgmlib-ngpc
Most docs available here: https://devrs.com/ngp/files/ and its famous folder
My own experiments (20 years ago?): https://github.com/sodthor/ngpcdev in columns (playing ym tunes) or modplay
I'll check if I've got more docs in my old HDs...
btw, do you have a full bios source or do you debug it with an emu ?
RE: 4000 vs 4001 - sodthor - 07-17-2025
don't know if mame code may help, but I think you already have it
https://github.com/mamedev/mame/blob/master/src/devices/sound/t6w28.cpp
RE: 4000 vs 4001 - KanedaFr - 07-18-2025
I'm disassembling the ngpc bios using Ghidra and the ngpc loader
Thanks to this, I also found and extracted its own sound driver...which I'm also disassembling in parallel.
I browsed several open source emulators for informations but it's not explained how it works exactly.
For exemple, you have to activate a mode to direct access the t6w28 from the cpu.
the several sound drivers (like yours) don't use z80 irq nor nmi.
Btw, Your PSGLib is perfect for my current needs , thanks!
I only need to understand how this all works before blindly use it.
RE: 4000 vs 4001 - sodthor - 07-18-2025
I also sent you a PM with some links via this forum.
RE: 4000 vs 4001 - KanedaFr - 07-19-2025
Edit :
It's documented on neopop
Even the direct Access to DAC.
RE: 4000 vs 4001 - KanedaFr - 07-20-2025
About the initial question, the K1SoundSimul has the answer : left and right.
Of course, the stereo is only available on the headphone.
The bios use the 2 ports for tune but only One for noise.