Hello Keith,
This question is regarding your Chibisound described at
https://www.chibiakumas.com/z80/platform2.php
for the MSX 1 you describe loading the mixer register,which is register 7,
with the value --NNNTTT.
Don't you need to set bit 7 to 1 and bit 6 to 0 when setting
the mixer register (register 7) in the AY sound chip on an MSX 1?-
otherwise it may damage an MSX computer or make the joystick malfunction.
In other words the wrong register value in the mixer register
can cause a short circuit in an MSX and so damage the
computer.
In other words the binary register value should be 10NNNTTT and not
--NNNTTT.
For an example reference the problem is mentioned here
https://www.msx.org/forum/msx-talk/emul ... in-openmsx
But you don't mention it.
This register mixer problem is specific to MSX as far as I am aware.
I think this is the first example I have seen of 8 bit computer software
that has the possibility of damaging the hardware (usually writing buggy
software does not damage the hardware)