Hah. Actually, the Plus keyboard is even wonkier. If a /(forward slash), *(asterisk), or +(plus) key is pressed on the Plus keyboard's keypad, the Plus keyboard inserts a shift down event into the stream. So, if you press any of those keys, the computer issues Inquiry, the keyboard responds with 0x71 (shift key down), then another Inquiry, then 0x79 (keypad event), then the computer issues an Instant command, the keyboard responds with the proper key code.
This is from Guide to the Macintosh Family Hardware.
But when I implement this, the OS believes the shift key is still held down, which is kind of intuitive unless MacOS is doing extra state tracking.
I'm guessing the keyboard is doing internal checking to see if either shift key is already held down, and if not, also inject a shift up event after the keypad response. It needs to handle the case of pressing shift keypad forward slash, and not inadvertently "release" the held down shift key.
So, I think the adapter needs to keep track of the ps2 keyboard's shift key state, and try to emulate what the Plus keyboard does here.
Super wonky that it's just those three keys, and they chose to inject shift key events.
This is from Guide to the Macintosh Family Hardware.
But when I implement this, the OS believes the shift key is still held down, which is kind of intuitive unless MacOS is doing extra state tracking.
I'm guessing the keyboard is doing internal checking to see if either shift key is already held down, and if not, also inject a shift up event after the keypad response. It needs to handle the case of pressing shift keypad forward slash, and not inadvertently "release" the held down shift key.
So, I think the adapter needs to keep track of the ps2 keyboard's shift key state, and try to emulate what the Plus keyboard does here.
Super wonky that it's just those three keys, and they chose to inject shift key events.