Read Track - IBM Multiprise 3000 Reference Manual

Read Track

Description: The Read Track command transfers multiple records to the channel.
This command is primarily for dump/restore utility programs. It sends all records
from a logical volume track without first having to determine the number of records
on the track and their formats. After reading the last record on the track, a pseudo
count area of 8 bytes with a value of X'FF' transfers to the channel. If channel
data transfer truncates because of an exhausted byte count or an exception
condition, no pseudo count area transfers to show the end of the track in the host
processor storage.
The byte count value should be at least as large as the maximum size record that
can be written on the track, plus the length of the R0 count and data areas, plus 8
bytes for the pseudo count area.
Chaining and Restrictions: Unit check status with the sense data containing
command reject with format 0, message 2 occurs if this command is:
The first Read Track command in a Locate Record or Locate Record Extended
domain is oriented to the first count area (including R0) following the orientation
established by the Locate Record command. The control unit sends each count,
key, and data area on the track until end-of-track. If the orientation is to home
address and there is no record zero, the command is terminated with unit check
status. The sense data includes No Record Found.
If end-of-track is detected before a count area other than R0 is found, only a
pseudo count area of 8 bytes of X'FF' transfers and the control unit does not
report an exception condition.
The following Read Track commands in a Locate Record or Locate Record
Extended domain cause the control unit to:
If no record zero is on the next track, the command is terminated with unit check
status. The sense data includes No Record Found.
Within the domain of a Read Trackset operation, the 'next' track is the track
corresponding to the next '1' bit in the Extended Parameter bit map. Within the
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Internal Disk Subsystem Reference Guide
Hex Code Data Address
DE The main storage location for the
first count area.
Not in a Locate Record domain that specified Read Tracks (0C) operation
code, or a Locate Record Extended domain that specified Read Tracks (0C) or
Extended Operation code of Read Trackset (0E).
Not immediately preceded by a Locate Record, Locate Record Extended, or
another Read Track command.
Advance to the next track
Be oriented to home address
Send each count, key, and data area (including R0) on the track until
end-of-track. (See "Operations in the Domain of a Locate Record or Locate
Record Extended" on page 4-2.)
Count
At least as large as the maximum
size record, plus R0 length, plus 8
bytes.