Prefetch Command (34H); Prevent/Allow Medium Removal Command (1Eh) - Seagate SCSI Interface Product Manual

SCSI Interface Product Manual, Rev. J
5.17

Prefetch command (34h)

The Prefetch command (Table 118) requests that the drive read and transfer the specified logical blocks to the
drive's cache memory. No data shall be transferred to the initiator.
Table 118: Prefetch command (34h)
Bit 7
Byte
0 Operation Code (34h)
1 Logical Unit Number
2 (MSB)
3
4
5
6 Reserved
7 (MSB)
8
9 Control [4]
Notes.
[1] An Immediate (Immed) bit of one indicates that status shall be returned as soon as the command descrip-
tor block has been validated. An Immed bit of zero indicates that status shall be returned after the opera-
tion is complete.
[2] A Relative Address (RelAdr) bit of one indicates that the logical block address field is a two's complement
displacement. This negative or positive displacement is to be added to the logical block address last
accessed on the logical unit to form the logical block address for this command. This feature is only avail-
able when linking commands. The feature requires that a previous command in the linked group have
accessed a block of data on the logical unit.
A RelAdr bit of zero indicates that the logical block address field specifies the first logical block of the
range of logical blocks to be operated on by this command.
[3] The Transfer Length field specifies the number of contiguous logical blocks of data that shall be trans-
ferred to the drive's cache memory. A transfer length of zero indicates that the contiguous logical blocks
up to and including the last logical block of the logical unit shall be transferred to the drive's cache mem-
ory. Any other value indicates the number of logical blocks that shall be transferred. The drive may elect to
not transfer logical blocks that already are contained in the cache memory.
If the Immed bit is zero and the specified logical blocks were successfully transferred to the cache mem-
ory, the drive shall return Condition Met status. If the Link bit (see paragraph 4.2.6) is one, the drive shall
return Intermediate-Condition Met status.
If Immed is one, and the unlocked cache memory has sufficient capacity to accept all of the specified log-
ical blocks, the drive shall return Condition Met status. If the Link bit (see paragraph 4.2.6) is one, the drive
shall return Intermediate-Condition Met status.
If Immed is one, and the unlocked cache memory does not have sufficient capacity to accept all of the
specified logical blocks, the drive shall return Good status. The drive shall transfer to cache memory as
many logical blocks as will fit. If the Link bit (see paragraph 4.2.6) is one, the drive shall return Intermedi-
ate status.
[4] See "Control byte," paragraph 4.2.6.
5.18

Prevent/Allow Medium Removal command (1Eh)

Not implemented by the drive. If received, the drive terminates with Check Condition status and sets an Illegal
Request sense key.
6 5
Logical Block Address [2]
Transfer Length [3]
4 3
Reserved
2 1
Immed [1] RelAdr [2]
(LSB)
(LSB)
161
0