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1996-10-30
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OSHTTRP2 - MEMORY PROBLEMS UNDER OS/2
02/07/96
=======================================================================
Memory Problems under OS/2--All OS/2 Releases
=======================================================================
Please Read Entire Document for Full Explanation of Procedures
--------------------------------------------------------------
DESCRIPTION
Under OS/2, memory problems can cause a TRAP0002 or other TRAP error
messages. These traps and their associated register information can
vary, and usually occur intermittently.
A TRAP0002 message indicates that the operating system detected a
hardware memory-parity error on the system board or on an expansion
adapter.
Memory problems also can result in the following symptoms:
* Other intermittent lockups, traps, or IPEs
* Intermittent application errors
* "Snow" or similar on-screen noise corruption.
RESOLUTION
The common sources of these problems are:
* Mismatched memory, such as single in-line memory modules (SIMMs) of
differing speeds or from different manufacturers. This is the most
likely cause if you recently added RAM to the system, or if the
system is a "home-grown" or no-name clone assembled from various
parts. SIMMs of different classes (such as 1- by 3-bit and 1- by
9-bit SIMMs) should never be mixed. Also, 1- by 9-bit SIMMs are more
reliable than 1- by 3-bit SIMMs.
* Slow memories: Some 486 and higher systems require 60-ns or 70-ns RAM
chips.
* Cache problems and other memory parity errors.
Solutions include:
* Removing defective SIMMs
* Replacing SIMMs
* Reseating a PCMCIA DRAM card
* Disabling shadow RAM
* Disabling "hidden refresh" and "fast decode enable" if your system
has an AMI BIOS
* Tuning wait states
* Disabling cache during installation
* Turning turbo switch off
OS/2 is a 32-bit operating system that handles data in 32-bit words,
and some systems with timing problems might encounter problems with
OS/2. DOS and other operating systems do not stress a system's memory
the way OS/2 does. For example, DOS uses 1 MB of low memory, while OS/2
is loaded into high memory that has never before been stressed by an
operating system. DOS is a single-task operating system, while OS/2 is
multitasking, which also stresses the memory in an OS/2 environment.
TRAP0002 errors almost always are memory-related, and other traps can
be too. Traps that occur intermittently or during heavy memory use,
such as the simultaneous use of multiple Windows applications, are
resolved by removing or replacing RAM.
On IBM hardware, possible causes of a TRAP0002 error include:
* 110 error: System-board memory-parity error
* 111 error: Memory-expansion adapter parity error
* 112 error: Watchdog timer error (could be hardware or software)
* 113 error: DMA arbitration error (could be hardware or software)
The most common type of TRAP0002 error is caused by memory, but also
can be caused by a system board, a Micro Channel adapter failure,
timing problems, and other hardware errors, particularly those
associated with ISA bus-mastering adapters. A TRAP0002 error is rarely
caused by software errors, because software usually does not access
the processor's nonmaskable interrupt (NMI) line. The NMI line is set
when the system detects a memory parity error. A TRAP0002 error occurs
only when the NMI line is set.
When any trap occurs, especially a TRAP0002:
* Check the failing system for mismatched SIMMs from different
manufacturers or different classes.
* Make sure all RAM is of the same model and speed.
* Contact the suppliers of the RAM chips or the memory adapter to have
these components tested.
When a memory-expansion adapter is used, make sure the SIMMs on the
card are from the same manufacturer and are the same speed as those on
the motherboard. If a problem is traced to an expansion adapter, check
with the system's manufacturer to find out if the adapter is
recommended for your system. Because memory-parity errors are caused by
timing-related problems, try placing the adapter in another slot to
reduce the distance between the adapter and the processor, and to
reduce memory access time.
Make sure the memory wait states are matched to the speed of the
processor bus. Some systems automatically tune these wait states;
others let you change these settings, and still others require memory
of a certain rated speed or higher. A 486DX2/66 system has a 66-MHz
internal bus, but its external (processor) bus, which connects to the
memory and other system components, runs at 33 MHz. This system can
operate with zero wait states only if it is equipped with 60-ns, or
faster, RAM. If the system has 70-ns or 80-ns RAM, it must be set up
for one wait state. The processor speed relates to wait states as
follows:
Memory Speed Required
Processor Clock Period for 0 Wait State
--------- ------------ ---------------------
486DX/25 40 ns 80 ns
486DX/33 30 ns 60 ns
486DX/50 20 ns 40 ns
Because the SIMM is precharged on one clock cycle and accessed on the
next, its speed rating is twice the period of the fastest clock rate
it can accommodate. If the clock period is less than half the SIMM's
rated speed, wait states must be introduced.
______________________________________________________________________
IBM disclaims all warranties, whether express or implied, including
without limitation, warranties of fitness and merchantability with
respect to the information in this document. By furnishing this
document, IBM grants no licenses to any related patents or copyrights.
Copyright (c) 1994, 1996 IBM Corporation. Any trademarks and product
or brand names referenced in this document are the property of their
respective owners. Consult your product manuals for complete trademark
information.