Seagate Ultra 320 manual Modify Data Pointer message format, Modify Bidirectional Data Pointer

It is recommended that the target not attempt to move the data pointer outside the range addressed by the command. Initiators may or may not place further restrictions on the acceptable values. Should the target send an Argument value that is not supported by the initiator, the initiator may reject the value by responding with the MESSAGE REJECT message. In this case, the data pointer is not changed from its value prior to the rejected MODIFY DATA POINTER message.

If an information unit transfer agreement is in effect the target shall not transmit a MODIFY DATA POINTER message.

Table 31: MODIFY DATA POINTER message format

Bit	7	6	5		4	3	2	1	0
Byte
0				EXTENDED MESSAGE (01H)
1				EXTENDED MESSAGE LENGTH (05H)
2				MODIFY DATA POINTER (00H)

3(MSB)

4	ARGUMENT
5
6		(LSB)

4.3.10MODIFY BIDIRECTIONAL DATA POINTER

The MODIFY BIDIRECTIONAL DATA POINTER message (see Table 32) is sent from the target to the initiator and requests that the signed data-out argument be added using two’s complement arithmetic to the value of the current data-out pointer and signed data-in argument be added using two’s complement arithmetic to the value of the current data-in pointer. The ENABLE MODIFY DATA POINTER (EMDP) bit in the Disconnect- reconnect mode page indicates whether the target is permitted to issue the MODIFY BIDIRECTIONAL DATA POINTER message. The target shall only issue the MODIFY BIDIRECTIONAL DATA POINTER message dur- ing a bidirectional command.

It is recommended that the target not attempt to move the data-out pointer or the data-in pointer outside the range addressed by the command. Initiators may or may not place further restrictions on the acceptable val- ues. Should the target send a data-out argument or a data-in argument value that is not supported by the initi- ator, the initiator may reject the value by responding with the MESSAGE REJECT message. In this case, both the data-out pointer and the data-in pointer are not changed from their values prior to the rejected MODIFY BIDIRECTIONAL DATA POINTER message.

If an information unit transfer agreement is in effect the target shall not transmit a MODIFY DATA POINTER message.

90 Parallel SCSI Interface Product Manual, Rev. A