A86: Down-left fix

To: <assembly-86@lists.ticalc.org>
Subject: A86: Down-left fix
From: "David Phillips" <david@acz.org>
Date: Sun, 6 Jun 1999 03:24:38 -0500
Delivered-To: assembly-86-outgoing@towerguard.unix.edu.sollentuna.se
Delivered-To: assembly-86@lists.ticalc.org
Reply-To: assembly-86@lists.ticalc.org

Aaron Curtis pointed out how to avoid the dreaded down-left bug yet still
use _get_key.  _get_key (from the acz include files) is equivalent to
_getky, but a heck of a lot faster, because it doesn't convert the scan
codes into OP2, just A.  Clem pointed that one out.

Down-left or other equivalent combos cause the hardware to trigger (or set
the interrupt mode?) an on interrupt instead of a timer interrupt.  This
causes the wrong interrupt to get refreshed/reset.  Bit 0 of port 3 will
have the current interrupt mode when read from inside an interrupt handler:

 reset -- timer
 set   -- on (or down-left)

So, if it's set, you don't want to call $01a1 (patched) in your interrupt
handler.  As he also pointed out, this info was on 86 Central the whole
time.  And, as I just checked, it's in the Sqrxz source code.  Being dumb, I
just never put two and two together and realized how to fix it.  Simple,
fixes down-left and allows you to have 8 directional movement in your
programs.

I attached my modified grayscale interrupt handler that fixes this bug.

--
David Phillips <david@acz.org>
http://www.acz.org/

gray.asm