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Q119853: INFO: PC Hangs While Running a Communications Application

Article: Q119853
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 06-APR-2000

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
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SUMMARY
=======

This article provides information about a problem that has appeared on recently
manufactured IBM PCs and PC compatibles. Many of these machines incorporate the
Peripheral Component Interface (PCI) bus, giving the impression that the problem
may be somehow related to this bus. The problem, however, can occur on machines
with other bus architectures. An obvious symptom of this problem is that when a
comm port is opened and closed a couple of times, the machine hangs, forcing the
user to reboot the PC.

MORE INFORMATION
================

There is a problem with a Super I/O chip (SMC '665) that many OEMs used to
provide serial ports on their latest generation (typically PCI-bus-based) PCs.
This problem can (and has) shown up on PCs that do not have a PCI bus. Having
the bad chip is all that is needed to cause this problem.

The problem is that if you reset the first in, first out algorithm (FIFO) by
clearing and then enabling it when the port is initializing, and there is
already a character in the receive FIFO, the comm driver gets an indication that
a new character has been received. The driver, of course, tries to get this
character. Unfortunately, the driver keeps finding that a new character is
available even if no more characters have been received. In this case, you can
do nothing short of a cold reboot to get rid of this indication. Any workaround
should, therefore, avoid this situation altogether.

A workaround involving a driver is to disable the FIFO, read a character, then
reenable it. A workaround if you do not have access to a driver is to disable
the FIFO feature of the 16550 UART. You can accomplish this by editing (adding
the entry if it does not exist) the COMxFIFO key (x = 1, 2, etc. for COM1, COM2,
etc.) of the [386Enh] section in the SYSTEM.INI file. For example, the FIFO for
COM2 can be disabled with the following entry:

  [386Enh]
  COMXFIFO=0

NOTE: Disabling a comm port's FIFO reduces its data throughput.

The COMM.DRV communications driver shipped with Windows version 3.x and
SERIAL.386 shipped with Microsoft Windows For Workgroups version 3.11 do not
offer a workaround for this problem. Users of Windows for Workgroups version
3.11, however, can download an upgrade to SERIAL.386; this upgrade works around
the problem. Users of Windows version 3.x have to obtain a third-party
communications driver that implements a workaround (or explicitly disables the
FIFO) to solve the problem.

REFERENCES
==========


There is a fix available for this issue from Intel. See the following Web site:

  http://www.intercast.com/support/motherboards/desktop/archive/PremierePCIed/serial.htm

The third-party contact information included in this article is provided to help
you find the technical support you need. This contact information is subject to
change without notice. Microsoft in no way guarantees the accuracy of this
third-party contact information.

Additional query words: 3.00 3.10 WfW 3.11 COM freeze OpenComm CloseComm hung frozen

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Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1
Issue type        : kbinfo

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