I'm lost... :-/
I think you didn’t read my post in the way I intended, which caused a mental tangent that multiplied confusion and misdirection by a 100 fold 
.
As I said, block writes to registers 04H, 18H and 19H, and mask out bits 0-1 and 3-5 of register 08H. That’s all there is to it.
else if(*g_VGM_Pointer == 0x5C) // Y8950, write value dd to register aa
{
u8 reg = g_VGM_Pointer[1];
u8 value = g_VGM_Pointer[2];
if (reg != 0x04 && reg != 0x18 && reg != 0x19)
{
if (reg == 0x08)
value = value & 0xC4; // 0b11000100
MSXAudio_SetRegister(reg, value);
}
g_VGM_Pointer += 2;
}
You don’t want to let VGMs just write to any register without restrictions. What if it enables some interrupt that isn’t handled, it would lock up the machine.
In this particular case the issue was caused by register 18H & 19H.
Look into the Yamaha Y8950 manual for the function of registers 18H & 19H. You will see they control four GPIO pins on the Y8950. In the Philips, Toshiba and Panasonic sound modules these GPIO pins are all hooked up to different functions. Therefore, you must not write a GPIO value recorded on a Panasonic to a Philips (or vice versa), or undesirable stuff like muting the sound will happen.
Specifically, the function of GPIO3 is as follows:
- Philips NMS-1205: 0 = mute Y8950 sound output
- Panasonic FS-CA1: 1 = mute Y8950 sound output
- Toshiba HX-MU900: no function
The conflict is evident.
Out of extreme completeness, the other GPIO functions I know of are; on the Philips NMS-1205 GPIO0 controls whether the DAC is enabled (0 = muted), and on the Toshiba HX-MU900 GPIO0 and GPIO1 allow reading the “multi-sensor” keys of Toshiba’s HX-MU901 external keyboard. But generally, you should just leave these GPIO signals alone since detecting which of these modules is present would be difficult.
Anyway let’s move back to the other thread, because this has nothing to do with detection.