Mockingboard emulation should support 'inactive' function like real h/w

[tomcw]

Bug reported by Grouik on the French Touch page, in the comments.

Btw, we can also win a few cycles by cheating a little as AppleWin does not require sending an "inactive function" to AY8910 after each operation (unlike a real Mockingboad).

For the Mockingboard’s "bug", I noticed that at the time of my first tests with one MB. I do not remember what version of AppleWin I used (I apologize in advance if it has already been corrected or if I was just a bug with my PC or others. I did not do more tests since).

So, to set a value for one of the registers, systematically we must use this sequence of instructions (one way or another):

LDA #01 ; register #
STA $C401,Y ; ORA1 (data)
LDA #$07 ; Set fct « Set PSG Reg # »
STA $C400,Y ; ORB1 (fct)
LDA #$04 ; Set fct « Inactive »
STA $C400,Y ; ORB1 (fct)

LDA #$xx ; value to set
STA $C401,Y ; ORA1 (data)
LDA #$06 ; Set fct « Write DATA »
STA $C400,Y ; ORB1 (fct)
LDA #$04 ; Set fct « Inactive »
STA $C400,Y ; ORB1 (fct)

(sorry, you already know that…)

This is the working method for real APPLE II (and AppleWin).

But with AppleWin, we can just use:

LDA #01 ; register #
STA $C401,Y ; ORA1 (data)
LDA #$07 ; Set fct « Set PSG Reg # »
STA $C400,Y ; ORB1 (fct)

LDA #$xx ; value to set
STA $C401,Y ; ORA1 (data)
LDA #$06 ; Set fct « Write DATA »
STA $C400,Y ; ORB1 (fct)

without sending the "inactive function" after each other fct.
Working with AppleWin but no sound at all with a real MB.

This is not really a problem because all programs using a Mockingboard use the right method!

[tomcw]

Fixed in 74ac2a4.
Tests: AppleWin/AppleWin-Test@23a2cbb