Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!purdue!umd5!uvaarpa!babbage!mac3n
From: mac3n@babbage.acc.virginia.edu (Alex Colvin)
Newsgroups: comp.sys.ibm.pc
Subject: Re: interrupt handling -- more obscure details
Summary: intrflag()
Message-ID: <309@babbage.acc.virginia.edu>
Date: 16 May 88 14:45:51 GMT
References: <2045@optilink.UUCP> <539@siemens.UUCP> <2078@homxc.UUCP> <308@babbage.acc.virginia.edu>
Organization: University of Virginia
Lines: 27

Sorry about the spelling in that last note.

Also, what I really wanted to show is how to use such a test-and-set IFLAG
routine:

For example:

/* uninterupted read & clear long
 * good for counting interrupts, etc.
 * NOT safe against other processors
 */

long lreset(long *lp)
  { long l;             /* old value */
    int f;              /* saved IFLAG */
    f = intrflag(0);    /* inhibit */
    l = *lp; *lp = 0;   /* read & clear */
    intrflag(f);        /* restore flag */
    return l;
    }

This can be called with interrupts enabled or disabled.  It returns in the
same state.  In the meantime, it disables ("inhibits") for a while.

				-- INHIBIT SAVE,ON
				-- ...
				-- INHIBIT RESTORE