🚀 go-pugleaf

In article <11396@hydra.gatech.EDU>, ccastje@prism.gatech.EDU (John Adair) writes:
> How do programs read multiple keys pressed at the same time (not just
> Alt and 'X')?  Many multiple player games allow two players to share
> the keyboard.  Is there a way to get the 8042 to alternate scan codes
> between the two keys (i doubt it)?  Do I have to sit there and poll
> the keyboard port (0x60, I think), remembering that the first key has
> sent a 'make', but not a 'break', before the second key sends a 'make'?
> Is there a simpler way to do this?
> 
> Along the same lines, how do I discard the keypresses before (or as soon
> as) they reach the buffer, preferably without having to constantly 
> read in and discard characters?

For what it's worth:  In the interrupt list (some outdated version, you can
find the latest at SIMTEL20 PD1:<MSDOS.INFO>INTER###.ZIP) I find:

INT 15 - OS HOOK - KEYBOARD INTERCEPT (AT model 3x9,Xt2,XT286,CONV,PS)
	AH = 4Fh
	AL = scan code
	CF set
Return: CF set
	    AL = scan code
	CF clear
	    scan code should not be used
Note: Called by INT 9 handler to translate scan codes

In an older posting, Tom Almy (at the time <toam@tekgvs.labs.tek.com>) used
this interrupt to remap the AT keyboard's CapsLock to another Ctrl key.  It
works beautifully.

A solution to your problem would thus be to write your own interrupt handler
for int 15, which would simply check for the AH==4fh (leaving all other
functions to the original handler, of course), and then update a global
variable to reflect the ``key-pressed state'' according the the scan code,
and clear CF.  This way, nothing would even *get* to the keyboard buffer!
(For that matter, you couldn't even put the keyboard in Ctrl, let alone
Alt-Ctrl state, with means Ctrl-C and Ctrl-Alt-Del are trapped!).

Your main loop would simply read the global variable, and act accordingly (e.g.
`left-ctrl F': player A fires at B, *and* `right-ctrl J': player B fires at A
* Both player dead: Draw!   *** GAME OVER ***   Another duel? (y/n)? _ :-)
.. hm, better release int 15 before the `(y/n)?' ...

BTW: TC's User Guide gives an example of this kind of interrupt handling, for
which you don't need a single line of assembler.  Speaking of TC, your global
variable should be `volatile' (make shure the compiler won't skip even a single
``read'' of that variable!).

Hope this helps

Markus Fischer,    Dpt. of Anthropology, Geneva.