Scsi Command Status - Spectra Logic Spectra 10000 User Manual

10kdev_.book Page 40 Friday, March 12, 1999 9:44 AM
Transfer Length, Parameter List Length or Allocation Length (Varies, See Specific Command)
The transfer length specifies the amount of data to be transferred by the command. The
parameter list length is used to specify the number of bytes sent during the Data Out
phase. This field is typically used in command descriptor blocks for parameters that are
sent to a target. A parameter length of 0 indicates that no data will be transferred. This
condition is not considered an error.
Control Byte (Varies, See Specific Command) The control field is the last byte of every
CDB. The control field is defined below.
Bit
Byte
05 or
09 or
11
Vendor-Unique Field - (Bits 7-6) The vendor-unique fields, if used, are defined for each
specific command. The user does not need to support the Vendor-Unique definitions to
obtain specified performance.
Flag - (Bit 1) The flag bit specifies which message the target returns to the initiator if the
link bit is 1 and the command completes without error. The library does not support
linked commands and returns a Check Condition if this bit is set. This bit must be set to
0.
Link - (Bit 0) The link bit is used to continue the I/O process across multiple commands.
The library does not support linked commands and returns a Check Condition if this bit
is set. This bit must be set to 0.

SCSI Command Status

The library sends one status byte, during the Status phase, to the initiator after
completing each command. The following events can cause the command to be
terminated without entering the Status phase:
•
an Abort message
•
a Bus Device Reset message
•
a hard reset condition
•
an unexpected disconnect
The Status phase normally occurs at the end of each command. In some cases, however,
it may occur prior to transferring the command descriptor block.
Chapter 3
7 6 5 4
Vendor Reserved
Unique
3 2 1 0
Flag Link