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Path: utzoo!watmath!clyde!burl!ulysses!mhuxl!houxm!hogpc!houxt!ijk
From: ijk@houxt.UUCP
Newsgroups: net.micro.pc
Subject: LOW LEVEL I/O PROBLEM - FIRST READ IS GARBAGE, NEXT ARE ONE BEHIND.
Message-ID: <407@houxt.UUCP>
Date: Sun, 20-May-84 09:22:04 EDT
Article-I.D.: houxt.407
Posted: Sun May 20 09:22:04 1984
Date-Received: Tue, 22-May-84 07:13:38 EDT
Organization: ATT Information Systems, Holmdel NJ
Lines: 33

I've been playing around with interfacing with the ROM BIOS and DOS
function calls.  (I'm using standard assembler to do the low-level
work, with interfaces provided to 'C", per standard conventions).
When I try to interface to the Async device, I run into a weird problem
when I put my modem into analog loopback:
	-----------------------------------------
	/* the code looks like this */
	int i,inp;

	for (i=0; i<= 255; i++) {

		writecom(i);	/* send out char over port */
		inp = readcom();	/* read char back in */

		if ( i != inp)
			printf("i = %x, inp = %x\n");
		}
	/* writecom and readcom can either be DOS func 3 & 4 or
	 * calls to the ROM BIOS; no difference
	 */
	-------------------------------------------

The first char read is ALWAYS GARBAGE - from then on, I'm one char 
BEHIND (i.e., when i = 1, inp = 0, etc.).  It would appear at
first glance that a 1 char buffer is somehow inserted into the system,
but if I do a read first, I just hang, waiting for a char.

What's going on????  If anyones interested, I'll send them actual
assembler code as well.

Thanx in advance.
Ihor Kinal
houti!ijk