Re: 680x0 clr instruction

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Article #51581

#51581

From: Mike Park
Date: Wed, 05 May 1993 14:57

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derway@cco.caltech.edu (D. Erway) writes:

>The original 68000 clr instruction would do a read before write. This lead to
>headaches in device driver code, where reading an address does something. Does
>anyone know if the latter members of this family continue to do this, or if
>they gave up the stupid useless bus cycle? I am specifically interested in
>68030.

The same problem still exists in the 68030.  My suggestion to you
is to clear variables by assigning from a zero variable. ie:

static int zero = 0;
int* csr = 0xfff;   /* special hardware register address */

*csr = zero;  	    /* forces write; don't use *csr = 0; */

-- 
Mike Park            mikep@dragoman.com          (NeXT Mail OK)

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From: mikep@hack.dragoman.com (Mike Park)
Newsgroups: gnu.gcc.help
Subject: Re: 680x0 clr instruction
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Date: 5 May 93 14:57:56 GMT
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