Define Extent
Description:
The Define Extent command parameters define limits on operations
that follow, provide a blocksize value, and specify cache controls for the channel
program. This command resets orientation in the control unit.
Chaining and Restrictions:
Unit check status with the sense data containing
command reject with format 0, message 2 occurs if:
A Define Extent command is in the domain of a Locate Record or Locate
Record Extended command.
A Define Extent command is preceded in the same channel program by a
Define Extent or Set File Mask command.
If the addressed logical volume is a 3390 and a Define Extent command is
preceded in the same channel program by a Read IPL command.
The control unit requests 16 bytes of parameters from the channel. If the channel
sends fewer than 16 bytes, the command is rejected with unit check status. The
sense data contains command reject with format 0, message 3.
The Internal Disk verifies the parameters and reserved fields in their order in
Table 4-4, except it checks byte 1, bits 0 and 1 first. If an exception condition
exists in more than one parameter, only the first exception is reported.
Ending Status:
The control unit presents channel end and device end status after
it verifies the parameters.
Hex Code
Data Address
Count
63
The main storage location of the first parameter byte.
16
Define Extent Parameters
Table 4-4 shows the parameters of the Define Extent command.
Table
4-4. Define Extent Command Parameters
Byte
Parameter
0
Mask byte
1
Global Attributes
2–3
Blocksize in bytes
4–6
Reserved, must be zeros.
7
Global Attributes Extended
8–11
Beginning of Extent Address
12–15
End of extent address
Mask Byte – Byte 0
The mask byte replaces the file mask that can be used to inhibit or control certain
channel program operations. Byte 0 has the format shown in Table 4-5 on
page 4-9.
4-8
Internal Disk Subsystem Reference Guide
Summary of Contents for Multiprise 3000
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