Compaq AlphaServer ES45 Service Manual page 148

NOTE: If memtest is used to test large sections of memory, testing may take a
while to complete. If you issue a Ctrl/C or kill PID in the middle of
testing, memtest may not abort right away. For speed reasons, a check
for a Ctrl/C or kill is done outside of any test loops. If this is not
satisfactory, you can run concurrent memtest processes in the
background with shorter lengths within the target range.
Memtest Test 1 — Graycode Test
Memtest Test 1 uses a graycode algorithm to test a specified section of memory.
The graycode algorithm used is: data = (x>>1)^x, where x is an incrementing
value.
Three passes are made of the memory under test.
•
The first pass writes alternating graycode inverse graycode to each four
longwords. This causes many data bits to toggle between each 16-byte write.
For example graycode patterns for a 32 byte block would be:
Graycode(0) 00000000 Graycode(1) 00000001 Graycode(2) 00000003
Graycode(3) 00000002 Inverse Graycode(4) FFFFFFF9 Inverse Graycode(5)
FFFFFFF8 Inverse Graycode(6) FFFFFFFA Inverse Graycode(7)
FFFFFFFB
•
The second pass reads each location, verifies the data, and writes the
inverse of the data, one longword at a time. This causes all data bits to be
written as a one and zero.
•
The third pass reads and verifies each location.
You can specify the -f (fast) option so that the explicit data verify sections of the
second and third loops are not performed. This does not catch address shorts
but stresses memory with a higher throughput. The ECC/EDC logic can be used
to detect failures.
4-46 ES45 Service Guide