Ref: 11030067
Title: Zenith ZDS 248 Concurrent PC Server and Maxess
date: 12/5/89

Copyright 3Com Corporation, 1991.  All rights reserved.

On a concurrent PC server, Maxess gateway software was loaded using
LOADGW.  After a few minutes, the server hung and displayed the message
"Internal stack overflow."

3Com engineers recreated the problem with the following equipment:

Zenith ZDS 248 (286 PC)
ROM BIOS chip  444-423-7 (rev. 7)
Zenith DOS 3.3
3+ 1.3.1
3C503 adapter
Maxess 1.3.0


Adding NOSTACK to the AUTOEXEC.BAT file did not solve the problem.
(NOSTACK disables the BIOS swap from the user stack memory area of the
application to the internal stack memory area).  Likewise, adding the
line STACKS=N,S to the CONFIG.SYS file did not solve the problem.
(STACKS=N,S overrides the default stack resources n=9 and s=128.
N is the number of stack frames, and S is the stack frame size in bytes.
DOS allocates one stack frame from the available pool each time a
hardware interrupt occurs.)

To solve the problem, the engineers added the MAXTIMER.SYS device
driver to the CONFIG.SYS file.  MAXTIMER.SYS fixes a problem in
certain ROM BIOS implementations where pending interrupts are lost
because the BIOS routine does not check the status of the interrupt
controller before issuing an END OF INTERRUPT command.  The problem
is known to occur on IBM XTs and on pre-1987 ATs.

Note:  MAXTIMER.SYS (found on the Utilities diskette) must be the
FIRST device driver loaded.  If MAXTIMER.SYS is not installed and
the ROM BIOS date indicates that the interrupt problem may exist, a
warning message will be displayed when MMS loads.  For more
information about MAXTIMER.SYS, see a description of it in the
Maxess README file.

