Heike C. Zimmerer wrote: > Robert, > > my answer didn't make it to the avr-chat list for reasons I don't know and I > have no time to care about. > Here it is again, in direct email: > > -------- Original-Nachricht -------- > Delivered-To: h...@hczim.de > Return-Path: <li...@hczim.de> > Received: from localhost (localhost [127.0.0.1]) (uid 1000) by minni with > local; Fri, 08 May 2009 13:01:05 +0200 id 0061A00D.4A0410F1.00001EF1 > From: li...@hczim.de (Heike C. Zimmerer) > Newsgroups: lists.avr-chat > Subject: Re: [avr-chat] Mega644 bit test problem > References: <4a03fe30.6030...@engelking.de> > Date: Fri, 08 May 2009 13:01:03 +0200 > Organization: Mostly Harmless > User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux) > In-Reply-To: <4a03fe30.6030...@engelking.de> (Robert von Knobloch's message > of "Fri, 08 May 2009 11:41:04 +0200") > Cancel-Lock: sha1:pkIw4CMV/nyYeqt/h1Q2vNWhIwc= > Posted-To: lists.avr-chat > To: undisclosed-recipients: ; > > The following message is a courtesy copy of an article > that has been posted to lists.avr-chat as well. > > Robert von Knobloch <b...@engelking.de> writes: > > >> #define ASYNCCLK 0 >> [....] >> while ((ASYNCPIN & _BV(ASYNCCLK)) != 1) // Wait for clock >> high >> [...] >> > > >> This works fine. I want, however to use portb bits 1 & 3 for clock & >> data. I simply change to #define ASYNCCLK 1 >> and re-compile >> Now, nothing works and the code generated is much smaller (0xe5 bytes >> instead of 0x193 bytes for the working variant). >> > > If you change ASYNCCLK away from bit 0, the above while expression will > never yield true since you compare directly against the value of bit 0. > So the compiler is free to remove it entirely. The fault is the '1' on > the right side (instead of using the actual bit value or comparing > against 0). > > Heike > > > It is so obvious that I couldn't see it (usually I compare to '0'). Thanks a lot, Heike. Robert
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