Path: utzoo!attcan!uunet!lll-winken!ames!oliveb!apple!claris!wombat
From: wombat@claris.com (Scott Lindsey)
Newsgroups: comp.sys.apple
Subject: Re: Border color
Message-ID: <9104@claris.com>
Date: 19 Mar 89 03:02:34 GMT
References: <8903181756.AA05520@crash.cts.com>
Organization: Claris Corporation, Mountain View CA
Lines: 41

From article <8903181756.AA05520@crash.cts.com>, by mdavis@pro-sol.cts.com (Morgan Davis):
> Dan Bornstein describes the method by which one changes the border color
> register on the IIGS.  You have to be careful with the upper nibble in this
> register because it is used by the Real Time Clock (RTC).  However, Dan's
> example showed 16-bit memory access being made to the $E0Cxxx area.  Is it not
> unsafe to do this?  When you fetch 16 bits from a location here you could
> possibly be hitting a softswitch.  I think it might be better to drop into
> 8-bit accumulator mode when working in the peripheral RAM area.

As a general rule, probably so.  However, in this case, there is no soft-
switch at 0xE0C035 or in the high nibble, so it _is_ safe.

To add my macros to the fray, these two are used in tandem to set the border
on entry to a section of code and restore it on exit.  Admittedly, these are
not the most efficient pieces of code, but they're fairly clear and only for
debugging anyway.

#define SETBORDER(color)	asm{	lda >0xE0C034	\
					and #0xF	\
					pha		\
					lda >0xE0C034	\
					and #0xFFF0	\
					ora #color	\
					sta >0xE0C034	\
				}
								
								
/* Reset border back to what SETBORDER saved */
#define RESETBORDER()		asm{	lda >0xE0C034	\
					and #0xFFF0	\
					ora 1,s		\
					sta >0xE0C034	\
					pla		\
				}


-- 
Scott Lindsey     |"Cold and misty morning. I heard a warning borne in the air
Claris Corp.      |    About an age of power when no one had an hour to spare"
ames!claris!wombat| DISCLAIMER: These are not the opinions of Claris, Apple,
wombat@claris.com |    StyleWare, the author, or anyone else living or dead.