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Q77246: System Clock Speeds Up When Using Task Swapper

Article: Q77246
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:5.0,5.0a,6.0
Operating System(s): 
Keyword(s): 
Last Modified: 03-DEC-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft MS-DOS operating system versions 5.0, 5.0a, 6.0 
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SYMPTOMS
========

Your system's time and date increment at an unusually fast rate when Task
Swapper is used. Your real-time clock is not affected, and rebooting the system
sets the time and date back to their correct values.

CAUSE
=====

The Task Swapper in MS-DOS Shell can cause the system clock to speed up on
systems where the speaker port (61H) is not properly initialized to an "off"
state.

WORKAROUND
==========

Task Swapper has code to manage programs that reprogram the timer. This code is
dependent upon the value returned by the speaker port (61H). In particular, the
lower two bits of this port (bits 0 and 1) control the speaker. When the
computer is first turned on, both of these bits should be cleared (zeroed) to
indicate the speaker is off. If your computer's hardware does not properly
initialize the speaker port, you can use the MS-DOS Debug utility to create a
program that will. Follow the instructions below to create SPKROFF.COM.

1. At the command prompt, start Debug by typing the following command and
  pressing ENTER:

  " debug " (without the quotation marks)

2. Enter the Debug commands as outlined below:

  Debug          Command
  Prompts        to Enter        Comments
  -------        --------        --------

  -              a 100            Assemble beginning at CS:0100
  nnnn:0100      in ax,61         Read port 61H into AX register
  nnnn:0102      and al,fc        Clear bits 0 and 1 - leave rest alone
  nnnn:0104      out 61,al        Write new value to port 61H
  nnnn:0106      int 20           Call DOS int 20H - terminate program
  nnnn:0108      <ENTER>          Press ENTER to end assemble process
  -              n spkroff.com    Name file SPKROFF.COM
  -              rcx              Replace CX register
  CX 0000
  :              0008             Place 0008 into CX register
  -              w                Write file
  Writing 00008 bytes
  -              q                Quit DEBUG

Each time you reboot your computer you should execute SPKROFF.COM before starting
Shell. It may work best to execute SPKROFF.COM from your AUTOEXEC.BAT file. If
you load Shell from AUTOEXEC.BAT, be sure to place the line that executes
SPKROFF.COM before the line that executes Shell.

Additional query words: 5.00 5.00a 6.00 dosshell task switcher DOSHELL

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Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS600 kbMSDOS500 kbMSDOS500a
Version           : MS-DOS:5.0,5.0a,6.0

=============================================================================

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