User's Guide

Chapter 3 Emulated DLT7000 SCSI Commands
Overview of Command and Status Processing
110 Quantum DX-Series Software Interface Guide
to the initiator as current pointers. There is only one set of current
pointers in the initiator at one time. The current pointers point to the next
command, data, or status byte to be transferred between the initiator's
memory and the drive. The saved and current pointers reside in the
initiator.
The saved command pointer always points to the start of the Command
Descriptor Block for the I/O process. The saved status pointer always
points to the start of the status area of the I/O process. The saved data
pointer always points to the start of the data area until the drive sends a
SAVE DATA POINTER message for the I/O process back to the initiator.
In response to the SAVE DATA POINTER message, the initiator stores the
value of the current data pointer into the saved data pointer for that I/O
process. The drive can restore the current pointer from the saved pointer
value for the active I/O process by sending a
RESTORE POINTERS
message to the initiator. The initiator then copies the set of saved pointers
into the set of current pointers. Whenever a drive disconnects from the
SCSI Bus, only the set of saved pointers is retained in the initiator. The set
of current pointers is restored from the set of saved pointers when the I/
O process is reconnected.
Reset Sequence 3
The DX-Series system supports the SCSI-2 soft reset option. When a SCSI
bus reset occurs, the library clears the SCSI bus as described in the SCSI-2
Specification.
Table 71 Command
Descriptor Block
Fields
Bit/Byte 7 6 5 4 3 2 1 0
0
1
2-3
4
5
Operation Code (07h)
Logical Unit Number
(MSB)
Logical Block Address
(LBA)
Logical Block Address
(LBA)(LSB)
Transfer Length, Parameter List Length, or Allocation Length
Control