21 read (6) command, Read (6) command – Seagate Fibre Channel Interface User Manual
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Fibre Channel Interface Manual, Rev. D
12.21
Read (6) command
The Read (6) command requests the disc drive to transfer data to the initiator.
Field definitions (listed alphabetically)
Control
See Control Bytes in Section 11.2.1.6.
Logical Block Address
The logical block at which the read operation will begin.
Transfer Length
The number of contiguous logical blocks of data to be transferred. Any number other than 0 indicates the number of logical
blocks that are transferred.
0
Transfer 256 logical blocks.
The data value most recently written in the addressed logical block is returned.
Read data transfers with the initiator do not begin until at least one full sector of data is available in the disc
drive data buffer. For multiple sector reads, the transfer of data continues until the number of blocks specified
in byte 4 of the CDB has been read and transferred or until an unrecoverable error is detected.
Data transfer could stop if the option to stop on recovered error is selected.
The initiator closes the loop after sending one or more commands. For a Read (6) command, the disc drive
arbitrates depending on the value of the Buffer Full Ratio Set in Page 2 of the Mode Select Data (see Section
12.11). After data transfer has been initiated with an initiator, the disc drive does not close the loop unless the
buffer is empty or the transfer length is exhausted.
The initiator must accept all data presented to the initiator after sending this command until the disc drive
sends Completion Status. (The disc drive may close the loop and re-arbitrate depending on the availability of
data in the buffer while executing this command and the initiator may prematurely terminate this command by
creating the Reset condition or by sending an Abort, Clear Queue, Target Reset, or Selective Reset).
Sense Data is valid after this command is executed and Completion Status is sent. If the Address Valid bit in
the Sense Data is true (1), the Sense Data Logical Block Address (Information bytes) points to the last logical
block accessed by the disc drive. If the Address Valid bit in the Sense Data is false (0), the Sense Data Logical
Block Address bytes are not valid.
Table 171: Read (6) command (08h)
Bit
Byte
7
6
5
4
3
2
1
0
0
0
0
0
0
1
0
0
0
1
0
0
0
(MSB)
Reserved
Logical Block Address
2
3
(LSB)
4
Transfer Length
5
Control
08h
Table
number