#545 Limit MSX-AUDIO I/O access

[Laurens Holst]

Currently, the limits on accessing the I/O of the MSX-AUDIO are not emulated.

The limitations are described in Table 2-2 on page 10 of the application manual:

http://map.grauw.nl/resources/sound/yamaha_y8950.pdf

Address write: 12 cycles
Data write: 12 or 84 cycles

These are quite specific numbers, but probably some further testing is required to confirm them, as well as the behaviour when access is too fast.

[Laurens Holst]

After a test with cycle-accurate timing on turboR, I have established that the required wait after an address write is exactly 11 MSX-AUDIO clock cycles.