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SCSI PACKETS
7-12
7
Some SCSI controllers return a "check" status on the first command sent to
them after power-up or reset. The SCSI firmware retries the command if the
controller returns "unit attention" request sense information and if you put a
number that was one or greater into the retry field in the attach packet.
Otherwise, the request-sense data is returned to you. You can then retry the
command.
The first table below shows the details of an attach/detach packet for disk. The
second table shows the details of a attach packet for streaming tape. A third
table details the 384-byte ($180-byte) work area specified in the attach packet
and used for all subsequent commands. The work area is normally not
examined by you except when the "additional status" bit is set (refer to the
packet status codes in Chapter 3). On most operations involving data transfer
(except scatter/gather) in which DMA is used, the "sector number in error",
"transfer address", and "command error word" can be used to assist error
handling.
New Packet
Even Byte \
Odd Byte \
FC B8 74 30
+$00 Controller LUN Device LUN
+$02 Status Byte 0 Status Byte 1 (Note 1)
+$04 0 0 Step Rate
+$06 0 0 Number of Heads
+$08 Number of Cylinders
+$0A Precompensation Cylinder
+$0C Logical Sectors per Track
+$0E 0000
+$10 SCSI Disk Attributes
+$12 Controller Type Drive Type
+$14 0 0 Function Code (78)
+$16 Interrupt Level Vector Number
+$18 Status Byte 2 Status Byte 3 (Note 1)
+$1A 0 0 Retry Count
+$1C Physical Bytes per Block