Re: A86: Down-left fix

To: assembly-86@lists.ticalc.org
Subject: Re: A86: Down-left fix
From: ComAsYuAre@aol.com
Date: Sun, 6 Jun 1999 08:20:13 EDT
Delivered-To: assembly-86-outgoing@towerguard.unix.edu.sollentuna.se
Delivered-To: assembly-86@lists.ticalc.org
Reply-To: assembly-86@lists.ticalc.org


is there any way to put this patch into a tsr so that the bug is totally 
gone?  or is it going to mess with the on key or something?


In a message dated 6/6/99 4:27:13 AM Eastern Daylight Time, david@acz.org 
writes:

> 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.