User`s manual

SIOP Firmware Structures

B-4 Single Board Computers SCSI Software UserÕs Manual

Bit 30 -- TARGET

If the INTATR bit is not set and the TARGET bit is set then the Firmware

operates in target mode. This bit designates the information in the structure to

contain control information in regards to a target mode request as indicated by

either the T_EXEC or T_WAIT bit in this field. The T_EXEC and T_WAIT bits

are mutually exclusive. Other bits in the command control field are examined

and used as indicated by their target definitions.

Bit 29 -- CONFIG

The configuration control field has the lowest priority of the three mode

control bits which the Firmware examines. If the INTATR bit and the

TARGET bit are cleared and the CONFIG bit is set then the Firmware operates

in the configuration mode. This bit designates the information in the structure

to contain control information in regards to a configuration request. The other

config defined bits are mutually exclusive. Only one configuration mode

request may be executed per command entry call. If this is the only

configuration mode bit set in the command control field then no other

parameters within the command structure are examined and the command

request is handled as a NOP with GOOD status returned.

Bit 18 -- PAR

initiator mode

If set, parity is checked during data transfers. If a parity error is detected a

parity error status is returned but no indication of the byte(s) in error is

returned to the user.

Bit 17 -- FIRST

initiator mode

Setting this bit overrides the normal FIFO ordering of the device queue. The

Firmware places this siop_struc at the head of the device queue to ensure it is

the next command sent to the specified device.

This bit is important in situations where the user wishes to send an

uninterrupted sequence of command requests to a specific device. An

example of this would be a large read, where the number of blocks required

by the user exceeds the block capacity of a 10-byte CDB. The single read must

be broken into a sequence of separate but contiguous commands to the device.

The first read command sent to the Firmware would not set the FIRST bit set;

however, all subsequent command requests in this read sequence would have

this bit set.