Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!amdahl!ems!pwcs!elric!billk
From: billk@elric.UUCP (William A. Karns)
Newsgroups: comp.sys.ibm.pc
Subject: Com port vs. floppy drive
Keywords: DMA Interference?
Message-ID: <574@elric.UUCP>
Date: 9 Sep 88 14:52:38 GMT
Organization: Unisys Inc.,  Eagan, MN, USA, 55121
Lines: 27

We've been experiencing a problem around here with a mysterious interaction
between serial ports and the floppy drive.  This problem seems to be confined
to Unisys PC/microITs equipped with 2 serial ports, 1 floppy drive and 1
hard drive (which is not to say that changing the value on one of these
parameters alleviates the problem :-).  We generally run MSDOS 3.2 around here,
but I wouldn't swear the problem is confined to this version.

The problem is this:

After an unknown sequence of events involving access of the serial port (#1 or
#2 or both), the floppy drive is rendered inaccessible, i.e., it can be neither
read or written.  One curious phenomenon occurs:  if a file is written to the
hard disk from Framework II, the floppy drive is then available.  This does NOT
occur if a file is written to the hard disk using other programs we have tried
(BRIEF, edlin, . . .)

We've speculated that DMA is involved, and spent a small amount of time writing
a small 'c' program to check the status of the floppy controller, and then
reset it, but our efforts have been to no avail.  The BIOS system call to check
the status indicates the drive is ready when it is obviously not!

Any assistance would be mucho appreciatedo.

-- 
Bill Karns                      "Marriage is a means, not an end."
UNISYS CSD Technology Transfer 
(612-681-6075)
billk@elric.UUCP            ..!uunet!rosevax!elric!billk