
channel to make this determination, execution is terminated with status that
includes unit check (Command Reject, format 0, message 3, CCW byte count
less than required). If it is the pseudo count field then the track image transfer
is complete, the remainder of the track is erased.
2. Otherwise they are treated as the count area of a user data record, see “Write
Count, Key, and Data” on page 4-86. Unlike a Write Count, Key, and Data,
execution is terminated with status that includes unit check (Command Reject,
format 0, message 3, CCW byte count less than required) on this command if
the channel does not provide enough bytes to fully write the record.
3. Once all of the bytes for the record have been processed, execution returns to
the first step (check for a pseudo count field).
When the control unit detects an invalid or incomplete track image condition, the
results of the write operation on the track will be unpredictable. If this is not the first
track image in the domain, the track images transferred by the preceding Write Full
Track commands will be written on the device.
The second and subsequent Write Full Track commands in a Locate Record
domain attempt to advance to the track that corresponds to the next ‘1’ bit in the
Extended Parameter bit map, orient to Home Address, transfer the track image,
and write the track image on the device.
Channel End and Device End status is presented when data transfer from the
channel is complete. If this is the last Write Full Track command in the domain this
status will be delayed until the update has been committed.
If the control unit determines that there is insufficient space on the track to write the
complete track image, the operation is terminated with status that includes unit
check (Invalid Track Format). The residual count in the CSW will not necessarily
indicate the amount by which the length of the track image exceeded the available
space on the track.
At the completion of command execution, the control unit is oriented to the data
area of the last record written on the track.
Programming Note:
The byte count of the Write Full Track CCW must contain a value that is
equal to sixteen bytes for Record Zero, plus the number of actual bytes to
be formatted as user data records, plus eight bytes for the pseudo count
area.
If only Record Zero is to be updated on a track, the track image must
consist of the Record Zero count and data areas, followed by a pseudo
count field. After the R0 is updated the remainder of the track will be
erased.
The pseudo count field is not written on the track. Its purpose is to indicate
that a complete track image is transferred from the host to the subsystem.
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