4000 vs 4001

[KanedaFr]

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 ?

[KanedaFr]

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

[sodthor]

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 ?

[sodthor]

don't know if mame code may help, but I think you already have it
https://github.com/mamedev/mame/blob/mas.../t6w28.cpp

[KanedaFr]

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.

[sodthor]

I also sent you a PM with some links via this forum.

[KanedaFr]

Edit :
It's documented on neopop
Even the direct Access to DAC.

[KanedaFr]

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.