OSOTCACH - INTERNAL AND EXTERNAL CACHE PROCESSOR INFORMATION
11/27/95

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          Internal and External Cache Processor Information
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Please Read Entire Document for Full Explanation of Procedures
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DESCRIPTION

Enabling cache (either internal or external) results in system lockups 
or traps. The traps can be, but are not limited to, TRAP0002, TRAP000D, 
TRAP000E, and SYS3175.

RESOLUTION

Disable the cache.

This is a hardware issue. If the information in this document does not 
solve the problem, the hardware vendor must address it.

Following are some reasons why the problem occurs.

Internal Cache
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The i486 and Pentium have cache built into the processor. This cache is 
rarely involved in any problems, but if disabling this cache does 
eliminate the symptoms, then one of two issues exist. Either a timing 
issue exists on the system board (which might or might not be able to 
be solved) or in the BIOS setup, or the processor is defective.

External Cache
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An external cache is static RAM (SRAM) that buffers memory accesses 
between the processor and RAM. This cache is more likely to be the 
cause of a failure. The issues listed give some idea of what to check.

Failing SRAM (Cache) Chips
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This might be the problem even if the cache worked in DOS. Because DOS 
has no memory protection, an invalid memory access because of a cache 
failure does not appear. In addition, OS/2 accesses memory that is not 
reported more often than DOS because of its multitasking environment. 
OS/2 also accesses at least 16MB of RAM under normal use; DOS accesses 
only a fraction of this.

Failing Cache Controller
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(See APAR PJ15584 for an example.)

Improperly Configured BIOS
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Check the RAM wait states and make sure they are set correctly. If 
there is no available documentation, set them to the highest value. If 
this solves the problem, decrease the value until the optimal value is 
found.

SRAM Chips Too Slow for Processor
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The system-board manufacturer has the specifications on this.

Example of Cache Failure
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* A system with 8MB of RAM and 256KB of SRAM worked fine. When 8MB of 
  RAM was added, for a total of 16MB, a trap occurred. The problem was
  that on the system board, the cache was designed so that if only 8MB
  of RAM was available, only the first 128KB of cache was accessed.
  When the RAM was upgraded, a defective SRAM chip in the upper 128KB
  of the cache caused the trap.

* After internal cache was enabled, a system trap occurred. Diagnostic
  tests of the processor ran fine. The solution was to buy a new system
  board and use the current processor. The most likely cause is a
  timing issue on the system, and that might have been resolved with
  BIOS setup.

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