HP 7957A Hardware Manual page 75

4·32. Seek Test Without Position Verify
Service Information
7957 A/7958A
Process: Logical seeks are performed with head 0 selected. The target tracks are
0, 1, 2, 4, 8 ... max logical, 0, max logical, max logical - 1, max logical -2, max
logical -4, max logical -8 . .. O. Faults occur if the Disc Drive Assembly PCA-A 1
reports a seek fault or ESDI communication problems arise. No attempt is made
to read a header to verify that a seek actually occurred.
Fault Reporting:
P1
1
(Disc Drive Assembly PCA-A1)
P2 2 (CEC PCA-A2)
P3 77 Disc Drive Assembly PCA-A1 self test fai led
P7
=
fault
#
P8
status associated with fault
# in P7
P9
status associated with fault
#
in P7
4·33. Read Write ECC Test
Limitations: A sector may be found which can be read and written 10 times
without an error yet still contain a slight media defect.. The defect could cause
some inconsistency in the ECC test results.
Process: There are two phases to the Read/Write ECC test.. The first consists of
finding a sector which can be written and read 10 times without a data error.
This sector is then assumed to be free of major media defects and so it is used
for the second phase which is the ECC portion of the test.
The test begins with a physical seek to the outside-diameter (00) self-test
cylinder which is at physical cylinder O. Starting on head 0, up to 5 sectors are
tried in an attempt to find one which can be read and written 10 times without
an error. If five sectors are tried unsuccessfully self-test fault #67 is generated to
indicated that the Read/Write retry count was exhausted. If any other fault is
detected during the read/write test it will be reported. As soon as a fault occurs
testing stops.
When a sector is found that can be read and written without an error the ECC
test is performed. This consists of writing an uncorrectable data error on the
sector. The sector is read and an uncorrectable error must be detected. A
correctable error is written and it must be read back as a correctable error. The
corrected data is checked to make certain that the errors were accurately
corrected. The final step is to rewrite the sector with no error. An ECC test
failure results in fault #68.
The tests outlined in the preceding two paragraphs are repeated for each head at
the 00 self-test cylinder and again for each head on the inside diameter (ID)
self-test cylinder.
Each time a sector is read as part of the read/write test the data is compared
against that which was written. Any mismatch which was not detected by the
ECC is flagged as a fault #66. Fault #66 is a self-test data compare error. The
data is read into various locations in the buffer space in an attempt to guarantee
the integrity of the buffer RAM addressing and the DMA.
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