Carte Blanche and Apples other than 2e

[Alex Freed <alex_news@mirrow.com>]

It came to my attention that the image selection from a keyboard doesn't 
always work right on a 2GS. I also know that it doesn't work on a 2+. 
This is not exactly a "bug" - rather the implementation is model specific.

To get the keyboard input CB monitors the Apple bus as it appears on the 
slot connector. If it detects a read from $C000 and the high bit of the 
data is set it is taken as a keyboard pressed event. Now it gets a bit 
technical. The signals available on the bus are Q3 and PH0 among others. 
In most cases the data is valid on a falling edge of the Q3 signal 
during PH0 high phase of the system clock. This is fine for latching the 
keyboard access on a 2+. Unfortunately the 2e uses a different design 
and the keyboad data becomes valid later than that. It also stays valid 
longer and can be latched on a falling edge of the ph0 itself. Since the 
vast majority of the A2s are of the 2e variety I chose to use the 2e 
timing in the default design.
If the 2+ timing is preferred it is a single Verilog line change. 
Unfortunately a fix that would work for *both* is not quite as simple. 
Not terribly hard either - just make a state machine running off the 50 
MHz system clock to latch the data somewhere at the right moment that 
works for both 2+ and 2e. Chances are it will also work for the GS.

I will probably do it eventually (if nobody does it before I do) but it 
is  not a first priority.

As for the VGA for GS the current design will support the standard video 
modes but not GS specific ones and not even the double-hires. Can be 
done but not the top priority either.

-Alex.