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Q151396: IBM PS/2 Computer Hangs When Start SNA Server SDLC Connection

Article: Q151396
Product(s): Microsoft SNA Server
Version(s): 2.0,2.1,2.11,2.11 SP1,3.5,3.51
Operating System(s): 
Keyword(s): 
Last Modified: 14-FEB-2002

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The information in this article applies to:

- Microsoft Windows NT Server versions 3.5, 3.51 
- Microsoft SNA Server, versions 2.0, 2.1, 2.11, 2.11 SP1, on platform(s):
   - the operating system: Microsoft Windows NT 
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SYMPTOMS
========

In certain instances, when you activate an SNA Server SDLC or X.25 connection on
an IBM PS/2 computer configured with an IBM MPA/A (or the Microgate equivalent),
the computer freezes and fails to respond to keyboard or mouse input.

CAUSE
=====

There are two problems which cause this problem to occur:

- The IBM PS/2 abios disk controller tries to allocate all available map
  registers for large data transfers. The standard SDLC device driver allocates
  2 when the SDLC connection is activated and never releases them. The disk
  controller hangs while waiting for the map registers. Slowly the whole system
  hangs as paging and disk access are stopped.


- The IBM PS/2 abios disk controller performs DMA data transfers at interrupt
  processor level. Microsoft Windows NT defines this as illegal (this may work
  on a single processor architecture, but in a multiprocessor environment it is
  dangerous, so Windows NT disallows it). The SDLC driver allocates a DMA
  resource, the disk controller generates an interrupt, and tries to acquire
  this DMA resource, and cannot, and never will be able to (the disk controller
  has just locked out the driver that owns it permanently). This causes the
  system to lock solid.

WORKAROUND
==========

Both problems are solved by applying the alternate Ibmsync.sys driver (intended
for PS/2 computers using the IBM MPA/A adapter or Microgate Microchannel
equivalent), described below. If the default Ibmsync.sys driver is used, the
first problem is solved through the support of a special DontUseMappedRegisters
registry setting for the IBMSYNC driver.

As documented in the SNA Server 2.11 Release Notes (Readme.wri), a special
version of the Ibmsync.sys driver supplied on the SNA Server 2.11 compact disc
can also be used to solve hang problems that may occur on IBM PS/2 computers. To
replace the existing driver, start the Windows NT Command Prompt and enter the
following commands:

    cd <snaroot>\system
    rename ibmsync.sys ibmsync.211
    copy <sna_cdrom>:\i386\system\hwsetup\ibmsdlc\ibmsync._sy  ibmsync.sys
    cd hwsetup\ibmsdlc
    rename ibmsync.sys ibmsync.211
    copy <sna_cdrom>:\i386\system\hwsetup\ibmsdlc\ibmsync._sy ibmsync.sys

NOTE: The Release Notes document the driver name as ibmsync._ys, though the
actual file name shipped on the SNA Server CD-ROM is ibmsync._sy.

Using the default Ibmsync.sys driver, the following registry setting causes the
driver to not request the use of mapped registers (though this version of the
driver does not correct the other hang problem observed with PS/2 computers).

WARNING: Using Registry Editor incorrectly can cause serious, system-wide
problems that may require you to reinstall Windows NT to correct them. Microsoft
cannot guarantee that any problems resulting from the use of Registry Editor can
be solved. Use this tool at your own risk.

Open Regedt32.exe and locate the following key in the system registry:

HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/IBMSYNC/Parameters

DontUseMapRegisters: REG_DWORD: 1

Once this option is configured, the SNA Server service must be restarted.

STATUS
======



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

If problems persist with the SDLC connection, a special traced version of
Ibmsync.sys is included on the SNA Server 2.11 compact disc that logs additional
failure conditions to the Windows NT system event log.

To apply the traced driver, start the Windows NT Command Prompt and enter the
following commands:

    cd <snaroot>\system
    rename ibmsync.sys ibmsync.211
    copy <sna_cdrom>:\i386\system\hwsetup\ibmsdlc\debug\ibmsync.sys
  ibmsync.sys

This special version of the driver logs internal driver errors when
sending/receiving information to/from the IBM SDLC/MPAA or Microgate adapter.
These new errors are logged in the Windows NT system event log as event 33 or
34.

Additional query words: 2.00 2.10 3.51 prodsna mg96 mg144 dsa usa

======================================================================
Keywords          :  
Technology        : kbWinNTsearch kbWinNTSsearch kbAudDeveloper kbSNAServSearch
Version           : :2.0,2.1,2.11,2.11 SP1,3.5,3.51
Issue type        : kbbug

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