User`s manual

SIOP Firmware Structures

B-8 Single Board Computers SCSI Software UserÕs Manual

Bit 6 -- LINK

initiator mode

If set, command in the CDB has the link bit set. The link field in the command

structure must point to the next command structure to be used. This bit must

be set for linked commands so the Firmware does not flag a linked command

operation as a protocol violation.

Bit 4 -- S/G

initiator mode

If set, scatter/gather is used for data transfers. The user must supply a

scatter/gather list. The pointer to the scatter/gather list is in the Data Pointer

field of the command structure. The scatter/gather list must be aligned to a

four-byte boundary.

Bit 3 -- D_PH

initiator mode

If set, the command contained in the CDB causes a data phase. For example,

test unit ready does not have a data phase associated with it; this bit should be

cleared. A read command has a data phase associated with it; this bit should

be set. A format unit command may or may not have a data phase associated

with it. The bit should be set if a defect list is to be included in the command.

If no defect list or defect list header is to be sent then this bit should be cleared.

Bit 2 -- R/W

initiator mode

If set, data direction is in to the initiator (read). If clear, data direction is out

from the initiator (write). This bit is ignored if the D_PH bit is not set.

Bit 1 -- ASYNC

initiator mode

If set, the Firmware initiates negotiations for asynchronous data transfers.

Normally, this bit is only set to place the SCSI device in a state that is

compatible with the state of the Firmware after a call to the initialization

module. If a synchronous data transfer rate has not been established then the

user should clear this bit to avoid unnecessary negotiations.