Command Block Definition; Command Control Block Format - Adaptec AHA-1740A Technical Reference Manual

adaptec
Careful host Target Mode software design is necessary to prevent ambiguity in the
notification process. If a CCB was just prepared but the MBO has not yet been
searched by the host adapter at the time the MBI entry is made to the host, the
host may choose to examine the MBI entry and not act on it, having already pro-
vided the needed CCB. The host should also examine the entire MBI space to be
sure that a previously supplied CCB which should have been able to service the no-
tification MBI entry was not already used for a previous operation that had been
posted by the host adapter but not yet serviced by the host. Proper care in host sys-
tem design will prevent these overlapping operations from becoming a problem.

Command Block Definition

The CCB specifies detailed information about a SCSI command. The format of a CCB
is shown below. Each of the fields is separately explained following the table.

Command Control Block Format

Byte Description
0 Command Control Block
Operation Code
1 Address and Direction Control
2 SCSI Command Length
3 Request Sense Allocation
Length/Disable Auto Sense
4-6 Data Length (Byte 4 most
significant)
5-20
Note
Value Meaning
00h SCSI Initiator command
01h Target Mode command
02h SCSI Initiator command with
Scatter/Gather
03h SCSI Initiator command,
residual data length returned
04h SCSI Initiator command with
Scatter/Gather, residual data
length returned
81h Bus Device Reset
Bits 7-5 CCB OP Code = 00, 02, 03, 04:
SCSI Target Id
CCB OP Code = 01: SCSI
Initiator Id
Bit 4 Outbound data transfer, length
is checked.
Bit 3 Inbound data transfer, length is
checked.
Bit 2-0 Logical Unit Number
AHA-1740A/1742A/1744