From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-help-return-9846-listarch-gcc-help=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 8343 invoked by alias); 17 Aug 2002 09:33:32 -0000
Mailing-List: contact gcc-help-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Archive: <http://gcc.gnu.org/ml/gcc-help/>
List-Post: <mailto:gcc-help@gcc.gnu.org>
List-Help: <mailto:gcc-help-help@gcc.gnu.org>
Sender: gcc-help-owner@gcc.gnu.org
Received: (qmail 8336 invoked from network); 17 Aug 2002 09:33:30 -0000
Received: from unknown (HELO independence.universe) (80.134.117.74)
  by sources.redhat.com with SMTP; 17 Aug 2002 09:33:30 -0000
Received: by independence.universe (Postfix, from userid 1000)
	id 0285513B84; Sat, 17 Aug 2002 09:33:37 +0200 (CEST)
Date: Sat, 17 Aug 2002 02:33:00 -0000
To: gcc-help@gcc.gnu.org
Subject: Bitfield packing 
Message-ID: <20020817073337.GA816@fericom.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.3.28i
From: eddy@fericom.net
X-SW-Source: 2002-08/txt/msg00144.txt.bz2

Hi, 

I am using gcc for a microcontroller application. I want to use
bitfields to describe the processor registers, 
similar to this: 

typedef union {
	IO_BYTE byte; 
	struct {
		IO_BYTE P30 :1; 
		IO_BYTE P31 :1; 
		IO_BYTE P32 :1; 
		IO_BYTE P33 :1; 
		IO_BYTE P34 :1; 
		IO_BYTE P35 :1; 
		IO_BYTE P36 :1; 
		IO_BYTE P37 :1; 
	} bit; 
} PDR2;

How does gcc handle bitfields like thisone? Above I have defined 8 bits,
are they distributed on several bytes with some optimization levels?

How do I setup gcc, so that it will always assign the bits 1:1 (no
packing/optimization)?

Thanks


Eddy Ilg