Locate Record Extended
Description:
The location and number of records to process and the operation to
perform are specified in the Locate Record Extended command parameters. See
page 3-3 for how the Locate Record Extended command makes an operational
domain. See “Locate Record Extended Operations” on page 4-34 for the specific
Locate Record Extended operation.
The Locate Record Extended command resets orientation in the control unit when
the command is received. Execution of this command establishes the orientation
state specified by the operation byte parameter before any data is transferred to or
from the logical volume.
Upon completion of the Locate Record domain, orientation is reset in the control
unit unless otherwise specified for the specific Locate Record Extended operation.
Chaining and Restrictions:
Unit check status with the sense data containing
command reject with format 0, message 2 occurs if:
This command is in the domain of a Locate Record or a Locate Record
Extended.
A Define Extent or Read IPL command does not precede this command in the
same channel program.
The control unit requests a variable number of parameter bytes from the channel,
consisting of fixed parameters (20 bytes) for all operation codes, and extended
parameters (variable length) for specified extended operation codes. The fixed
parameters specify the location and number of records or tracks to be processed,
the operation to be performed, and if an extended operation is specified, the
number of extended parameter bytes required. The extended parameters contain
additional control information for those extended operations requiring them.
The subsystem initially requests 20 bytes of parameters from the channel; if the
channel sends fewer than 20 bytes, the command is rejected with unit check status.
The sense data contains command reject with format 0, message 3.
Following verification of the data in the initial parameters, the subsystem requests
additional parameter bytes if the Operation Code in byte 0 is X
'
3F
'
, the Extended
Operation byte 17 specifies an Extended Operation that requires additional bytes,
and the Extended Parameter Length bytes 18–19 specify a length consistent with
the Extended Operation in byte 17. The number of additional bytes required by the
Extended Operation and specified in bytes 18–19 are requested from the channel;
if the channel sends fewer than the requested number of bytes, the command is
rejected with unit check status. The sense data contains command reject with
format 0, message 3.
The control unit verifies the parameters and reserved fields in their order in
Table 4-11 on page 4-28, except it checks byte 0, bits 2 through 7 and byte 17
first. If the control unit detects an exception condition in more than one parameter
in Table 4-11 on page 4-28, it reports only the first exception detected.
Hex Code
Data Address
Count
4B
The main storage location of the first parameter byte.
20,
21 or
22
Chapter 4. Command Descriptions
4-27
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