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HTTRP2.FAX
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1995-01-16
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OSHTTRP2 - MEMORY PROBLEMS
10/20/94
================================================================
MEMORY PROBLEMS
================================================================
Please Read Entire Document for Full Explanation of Procedures
----------------------------------------------------------------
Under OS/2, memory problems can cause a TRAP0002 or other TRAP error
message. These traps and their associated register information may
vary, and usually occur intermittently. A trap 2 message
indicates that the operating system has detected a hardware memory
parity error on the system board or on an expansion card. Memory
problems may also result in the following symptoms:
- Other intermittent hangs, traps, or IPEs
- Intermittent application errors
- "Snow" or similar on-screen noise corruption.
The common sources of these problems include:
Mismatched memory, such as Single In-line Memory Modules (SIMMs)
of differing speeds or from different manufacturers. This is
most likely 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 1x3-bit SIMMs and
1x9-bit SIMMs) should never be mixed. Also, 1x9-bit SIMMs are
more reliable than 1x3-bit SIMMs.
Slow memories: Some 486 and higher systems require 60ns or 70ns
RAM chips.
Cache problems and other memory parity errors.
Solutions include:
- Remove defective SIMMs
- Replace SIMMs
- Re-seat PCMCIA DRAM card
- Disable shadow RAM
- If the user has an AMI BIOS, disable "hidden refresh" and
"fast decode enable"
- Tune wait states
- Disable cache during installation
- Turning turbo switch off
OS/2 2.x is a 32-bit operating system that handles data in 32-bit
words, and some systems with timing problems may encounter
problems with OS/2. DOS and other operating systems do not
stress a system's memory the way that OS/2 does. For example,
the DOS operating system uses 1M 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.
Trap 2 errors are almost always memory related. Other traps may
also be memory related. Traps that occur intermittently or
during heavy memory utilization, such as the simultaneous usage
of multiple Windows applications, are resolved by RAM removal
and/or replacement.
On IBM hardware, possible causes of a Trap 2 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 Trap 2 error is caused by memory, but may
also be caused by a system board, a Micro Channel adapter
failure, timing problems, and and other hardware errors,
particularly those associated with ISA bus-mastering adapters. A
Trap 2 is rarely caused by software errors because software
usually does access to the processor's NMI line. The NMI line is
set when the system detects a memory partiy error. A Trap 2
occurs only when the NMI line is set.
When any trap occurs, especially a Trap 2:
- Check the failing system for mismatched memory SIMMs from
different manufacturers or different classes.
- Ensure 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 card 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
card, check with the system's manufacturer to find out if the
card is a recommended model for your system. Since memory parity
errors are caused by timing related problems, try placing the
card in another slot to reduce the distance between the card 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 66MHz internal bus, but its external (processor)
bus, that connects to the memory and other system components,
runs at 33MHz. This system can operate with zero wait states
only if it is equipped with 60ns RAM or faster. If the system is
equipped with 70ns or 80ns RAM, then it must be set up for one
wait state. The processor speed relates to wait states as
follows:
Processor Clock Period Memory Speed Required for 0 WS
486DX/25 40ns 80ns
486DX/33 30ns 60ns
486DX/50 20ns 40ns
Because the SIMM is precharged on one clock cycle and accessed on
the next, its speed rating is two times the period of the fastest
clock rate it can accomodate. If the clock period is less than half
of the SIMMs rated speed, then wait states must be introduced.