User's Guide

Commands: Log Select (4Ch) Page 51
Command Descriptor Block Field Description
The following table defines the fields in the CDB.
Field
Name Bytes Bits Description
PCR bit 1 1 The Parameter Code Reset (PCR) bit is used to reset log parameters.
If the bit is set (1) and the parameter list length is set to 0, all
accumulated values are set to 0. All threshold values are set to the
defaults.
Pages 0, 30, and 31 are not reset with this bit. When the PCR bit is set,
the PC bits in the CDB are ignored.
A PCR bit of 0 does not cause the parameters to be reset.
PC bits 2 6-7 The Page Control bits select one of four possible types of log
information. The settings of these bits are shown in a subsequent table.
Parameter
List Length
7-8 The Parameter List Length field specifies the length (in bytes) of the
parameter list to be transferred during the Data Out phase. A 0 length
indicates that no parameter data is to be transferred to the target.
Errors Detected in the Command Descriptor Block
The following conditions constitute errors that may be detected by the drive in
relation to the CDB. These errors cause a Check Condition. The request sense data
is set to Illegal Request, Invalid Field in the CDB.
• If the PCR bit is set and the parameter list length is not 0.
• A parameter list length that would cause a parameter within a valid page to be
truncated or otherwise incompletely initialized.
• The settings of the PC bits select the default threshold or default accumulated
values and the parameter list length is nonzero.
Use of the PC Bits
The Page Control bits (byte 2, bits 6-7) define the type of parameter values that are
to be sent to the drive. The following table lists the Page Control bit values for the
LOG SELECT CDB.
Bit 7 Bit 6 Type Requested Counts
0 0 0 Threshold values
0 1 1 Accumulated values
1 0 2 Default threshold values
1 1 3 Default accumulated values
USE OF DEFAULT VALUES TO SET CURRENT VALUES
The threshold values can be loaded with the default threshold values by setting the
PC bits to specify the default threshold values. The Parameter List Length must be
set to 0.
Likewise, the accumulated values can be loaded with the default accumulated
values by setting the PC bits to specify the default accumulated values. The
Parameter List Length must be set to 0.