Datasheet

Data Buffer Management
3-4 C141-C008
(2) Write operation
After data transferred from the INIT are stored temporarily in the data buffer, they
are written to the disk media. The basic write operation procedure is as shown
below.
1) When the IDD receives a command, it transfers the XFER_RDY flame to
INIT. Later it stores data transferred from the INIT to the data buffer (data
pre-fetch). At this time, the IDD locates the position of the data block on the
disk media specified by the command in parallel.
When storing of all the size of data specified in the XFER_RDY flame in the
data buffer is completed, the IDD performs Loop CLOSE processing.
2) When locating of the target data block on the disk media is completed, the
IDD writes the data in the data buffer to the disk media. If the target data
block location operation is completed during the data pre-fetch processing in
1), writing of data to the disk media is performed in parallel with the data
pre-fetch to the data buffer.
3) If the data transfer rate of the INIT (FC interface) is lower than the data transfer
rate of the disk drive, since the data pre-fetch of data that are to be written to that
data block is not completed, it may not be possible to write the data continuously
to the disk (data underrun). In this case, the IDD waits one disk revolution while
continuing to pre-fetch data from the INIT, then repositions the block that caused
the data underrun and continues the writing of data to the disk.
4) If all the blocks of data specified in the command have not yet been
transferred from the INIT, as writing of data to the disk media progresses, at
the point when the empty space in the data buffer reaches the amount
specified in the buffer empty ratio in the MODE SELECT parameter, the
IDD performs Loop OPEN processing and begins transferring the succeeding
data (data pre-fetch) after it transfers the XFER_RDY frame.
Writing of data to the disk media is performed in parallel and data transfer
with the INIT continues until the empty space in the data buffer is full or
until transfer of all the data specified in the command is completed. From
then on, the XFER_RDY data receiving are repeated until transfer of all the
blocks of data specified in the command is completed.
5) When writing of all the specified data is completed, the IDD reports the
status and terminates the command.