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From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.amiga.programmer
Subject: Re:   Short Hello World
Message-ID: <21736@cbmvax.commodore.com>
Date: 20 May 91 06:28:46 GMT
References: <1804@tardis.Tymnet.COM> <1991May7.001146.1830@cinnet.com> <dillon.7447@overload.Berkeley.CA.US> <1991May10.103117.4270@cs.umu.se> <1991May11.072139.781@starnet.uucp> <dillon.7621@overload.Berkeley.CA.US> <1991May13.220559.11706@visix.com> <my
Organization: Commodore, West Chester, PA
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kes.2644@amiga0.SF-Bay.ORG>
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In article <mykes.2644@amiga0.SF-Bay.ORG> mykes@amiga0.SF-Bay.ORG (Mike Schwartz) writes:
>In article <1991May13.220559.11706@visix.com> brett@visix.com (Brett Bourbin) writes:
>>Doesn't this also introduce problems with the custom chips, since you can
>>say something like "clear the COPPER 1 STROBE" with the CLR.W cop1xxx(AX)
>>command.  This would read the register before writing the zero.  I am not
>>sure about the COPPER STROBE, but I know some write-only registers get
>>very picky when you try to read them.

>I've tested clr.w on the copper strobes and it works.  

	Empirical programming, Mike!  Just because it works on your machine
doesn't mean it'll work on the machine someone down the street just bought,
let alone on the next generation of graphics chips.  When you read a write-
only register on a chip without a R/W line, it will latch a random value
from the bus.  This value may change from machine to machine, model to model,
or chip-rev to chip-rev.

	Stick to the guidelines - don't use clr on write-only registers.

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.commodore.com  BIX: rjesup  
Disclaimer: Nothing I say is anything other than my personal opinion.
Thus spake the Master Ninjei: "To program a million-line operating system
is easy, to change a man's temperament is more difficult."
(From "The Zen of Programming")  ;-)