Ciprico Rimfire 3880 - Manual (Page 94)

21020285 D User’s Guide
Chapter 5 Initiator Mode Pass-through Commands
Page 5 - 10 Initiator Pass-through Parameter Block Format
IAD Inhibit Automatic Disconnect - If you enable SCSI disconnect
privilege with the DIS bit of the General Options Board-control command (Bit
0 of Select Flags field), disconnects will automatically be tried for any
command. Use the IAD bit to disable SCSI device disconnect/reconnect
privilege for the current command. This can be important for performance
reasons.
0
⇒
Determine disconnect from the DIS bit of General Options command.
1
⇒
Ignore DIS bit, inhibit the disconnect privilege.
JSM Just Send Message - Use this bit to change the Initiator Pass-through
Command Parameter Block to a Pass-through Message Parameter Block. In
this Message mode, the adapter selects a device and only sends a message. This
provides a measure of error recovery at the host level.
0
⇒
Pass-through command operation as usual.
1
⇒
Use the Pass-through Message Parameter Block format.
This message-only format is illustrated on page 5 - 11, following the description
of the Pass-through command structure.
VME Memory Address
When the SCSI operation involves a data transfer, this field contains the
beginning address for the transfer. Note: transfers must be word-aligned.
If the SCSI command you are issuing does not require a data transfer, the
adapter ignores this field and the Address Modifier field.
Transfer Count
This field determines the number of bytes that will be transferred to or from
host memory. For some SCSI commands this is an indeterminate number. In
that case, there are two ways to use this field:
1. You can place a value in the field to represent the maximum number of
bytes the adapter may transfer. Then, if the target attempts to transfer
more data than this, the adapter will discontinue the operation and
return a Status Block.
2. Alternately, you could place a zero value in this field. This causes the
adapter to continue to accept data transfer requests from the target until
command is complete.
SCSI Command Descriptor Block
These 12 bytes of the Initiator Pass-through Parameter Block are reserved for
the actual SCSI command that will be passed to the drive. Except for the first
byte, which contains the command opcode, each SCSI command uses the bytes
for a different purpose; see a SCSI specification or vendor-supplied peripheral
documentation for details about the commands and fields.
SCSI commands may be 6, 10, or 12 bytes in length. Any of the 12 bytes
reserved for the SCSI command that are unused are ignored. The SCSI
command block is passed to the SCSI device exactly as presented. The RF3880
adapter doesn’t alter any of the fields you set up.