User's Guide
Page 50 DDS-4 SCSI Interface Manual, Rev. B
LOG SELECT (4Ch)
The LOG SELECT and LOG SENSE commands are used in conjunction with each
other. These commands allow the host to obtain and control statistical information
about cartridge usage and error rates. This information consists of counts related to
particular events that occur. Count thresholds can be established which
automatically generate log exception conditions.
The LOG SELECT command is used to preset counts of pages 2 and 3 to a specific
value or to reset the counts if the maximum count is reached. The log sense data is
also reset by a SCSI Bus Reset or a Bus Device Reset with the exception of the
page 30 and 31 data. That data cannot be reset by the initiator.
Counts of pages 2 and 3 can be read by the LOG SENSE command before a reset
and then restored after the reset by issuing the LOG SELECT command.
The log select data is transferred to the drive by specifying the log select page or
pages to initialize. Multiple pages can be affected by a single log select CDB.
However, the LOG SENSE command can only request one page at a time.
The log select parameter data is transferred to the drive to initialize page data. The
parameter data is organized using structures called log parameters. A log parameter
is made up of a parameter header that contains a parameter code that identifies the
log parameter to be initialized.
The drive determines the pages used by reading log sense page 0. Any request to
initialize an unused log page causes a Check Condition. The request sense data is
set to Illegal Request, Invalid Field in the CDB.
The log parameter codes within each log page used by the drive are determined by
reading each particular log sense page. Any attempt to specify an unused
parameter causes a Check Condition. The sense data is set to Illegal Request,
Invalid Field in the parameter list.
LOG SELECT Command Descriptor Block
The following table shows the layout of the CDB.
Byte
Bits
7 6 5 4 3 2 1 0
0 0 1 0 0 1 1 0 0
1 0 0 0 0 0 0 PCR 0
2 PC 0 0 0 0 0 0
3 0 0 0 0 0 0 0 0
4 0 0 0 0 0 0 0 0
5 0 0 0 0 0 0 0 0
6 0 0 0 0 0 0 0 0
7 MSB—Parameter List Length
8 Parameter List Length—LSB
9 vendor unique* 0 0 0 0 Flag Link
* This vendor-unique field is reserved and must be set to zero.