Improve support for Phasor's Echo+ mode

[tomcw]

Since I can't read the AY regs, then I don't even know the AY writes are working! EDIT: I can read the Echo+ AY regs (and this is now implemented in mb-audit).

NB. the Echo+ has a single 6522 and 2x AY's.

• try to play a tone on the AY channels
• try to read AY regs using different four MSB bits...

From Wikipedia:

Although there are only 16 registers, the four MSB bits of the 8-bit bus must be set to the factory default '0000' value when selecting a register. Incorrectly setting the MSB bits causes the chip to ignore the register change. General Instruments did take orders for customized MSB bits (factory set to other than '0000'). The chips made with customize-set MSB register bits allow the same processor to control more than one AY chip on the same bus (e.g. Mockingboard sound card for Apple or TurboSound for ZX Spectrum). There are many new-old-stock (NOS) chips on the secondary market with MSB bits factory set to a non-'0000' value. The non-0000 value can cause significant developmental troubles for designers and repair technicians. Software must be written to identify the correct value of the MSB bits on any given chip. Also, software must be changed or hardware added to allow these factory set MSB chips to be used in place of the default '0000' chips.

[tomcw]

From Wikipedia:

I fixed this, as it was wrong: The Mockingboard sound card for Apple II doesn't use customize-set MSB register bits. https://en.wikipedia.org/wiki/General_Instrument_AY-3-8910

[tomcw]

Also added these extra tests: 3b35651377c4a4a4acd460f561df5d64d656770b 180795e1811e3ac6f5b8afdcfc890daa9ed1ce0b 32b937a3a61b9f04632c6a26ce6d43c39ad99ad3

[tomcw]

Some observations about Phasor Echo+ mode: NB. This is from Phasor-native mode, and then using TAB to cycle (via "Software Selection") to Echo+ mode.

• TestAYTones: Echo+ outputs each AY channel to both left & right speakers (dual mono).
  • Specifically it outputs the right channel to the left one (but not left to right - see below: the press 'Q' case)
• TestAYTones: from Phasor-native mode, press '1' (ie. left speaker, 1st AY), then cycling through the 3 modes: for Echo+ -> MB, there's no noticeable increase in volume (output from same left speaker). NB. In Echo+ there's output on the right speaker too.
• TestAYTones: from Phasor-native mode, press '4' (ie. right speaker, 1st AY), then cycling through the 3 modes: for Echo+ -> MB, there's an increase in volume (output from same right speaker)
  • From MB mode, press '4' won't silence the right speaker (it just decreases the volume)
  • Then cycling back to Phasor mode, there's silence; then silence when cycling on to Echo+ and MB modes!
• TestAYTones: from Phasor-native mode, press 'Q' (ie. left speaker, 2nd AY), then cycling to Echo+ & MB, the tone can still be heard. NB. In Echo+ there no output on the right speaker.
• TestAYTones: from Phasor-native mode, press 'R' (ie. right speaker, 2nd AY), then cycling to Echo+ & MB, there's just silence.
• NB. In Echo+ mode, then 6522-A (physically mapped to $Cn00) isn't accessible. So (from MB or Phasor mode) using it to generate a periodic TIMER1 interrupt, and then switching to Echo+ mode means that you can't clear the interrupt, unless you switch our of Echo+ mode.

[tomcw]

Support Echo+ AY detection: 74a2a67d2c2c633965e505ee4ccdc80ef6e5a372

[tomcw]

Phasor DIP SW1=OPEN(Hardware mode selection), SW2=OPEN(Echo+)

mb-audit v1.3, TestAYTones:

Any key '1','2',...'6' outputs a tone to both speakers (and as more tones are enabled, then the volume increases).

[tomcw]

Remaining to do:

• [ ] Investigate whether the 2 AYs' latch addresses can be set independently and write to different AY regs + add tests.
• [ ] TestAYTones: improve UI - eg. display "PH"/"E+"/"MB" in a better location on the screen.
• [ ] For a real Echo+, then support detecting the TMS5220, and display it on the screen's "Speech" row.