Seagate Ultra 320 - Manual (Page 54)

40 Parallel SCSI Interface Product Manual, Rev. A )
If the responding negotiation message contains values the originating port does not support, the originating
port shall respond with a MESSAGE REJECT message.
2.12.2 When to negotiate
Each port shall maintain a negotiation required flag for each other port. A port shall set its negotiation required
flags to true for all other ports after a reset event. A port shall set its negotiation required flag to true for a given
port after an error occurs while transmitting a responding negotiation message to that port.
A SCSI initiator port shall set its negotiation required flag to true for a SCSI target port after an unexpected
COMMAND phase occurs when selecting without using attention condition (i.e., when selecting a SCSI target
port with information units enabled).
A logical unit reset has no effect on negotiation required flags or on transfer agreements.
After a reset event a port shall set its transfer agreements for all other ports to the default transfer agreement
(see Table 13).
A SCSI initiator port shall originate negotiation before sending a command to a SCSI target port whenever its
negotiation required flag is true for that SCSI target port. A SCSI target port shall originate negotiation before
accepting a command from a SCSI initiator port whenever its negotiation required flag is true for that SCSI ini-
tiator port. After successful negotiation or reaching the default transfer agreement, the negotiation required flag
shall be set to false.
A port may originate negotiation even if its negotiation required flag is false (e.g., to change the settings, as
part of integrity checking procedures, or, for a SCSI initiator port, after a SCSI target port has originated negoti-
ation). Negotiation should not be originated after every selection and reselection as this may impact perfor-
mance.
Note. SCSI target ports may have had their support for originating negotiation after power on disabled to
support illegal SCSI initiator device software. If a SCSI initiator port sends a command to a SCSI target
device that has been powered on (e.g., after a hot plug) that results in a unit attention condition, the
SCSI initiator port determines that negotiation is required and originates negotiation before the next
command. However, if the command is INQUIRY, REPORT LUNS, or REQUEST SENSE, a unit atten-
tion condition is not created. An invalid data phase may occur if the SCSI target port does not originate
negotiation. If the SCSI initiator port always originates negotiation before sending those commands,
the data phase runs correctly. When information units are disabled, a SCSI initiator port may originate
negotiation with its currently negotiated settings before each INQUIRY, REPORT LUNS, or REQUEST
SENSE command to avoid this problem. When information units are enabled, the selection without
attention results in an unexpected COMMAND phase that notifies the SCSI initiator port that negotia-
tion before each INQUIRY, REPORT LUNS, or REQUEST SENSE command is not needed.
2.12.3 Negotiable fields
Table 11 lists the fields that may be negotiated and the effects of successful negotiation on those fields by each
of the different negotiation messages. Ports shall implement a given message if they implement fields that are
negotiable with that message.
Table 11: Negotiable fields and effects of successful negotiation
Field name
Negotiation message pair
PPR WDTR SDTR
Transfer Period Factor
Negotiated
(valid values: 08h-FFh)
No requirement Negotiated
(valid values: 0Ah-FFh)
REQ/ACK Offset
Negotiated Sets to 00h Negotiated
Transfer Width Exponent Negotiated
(valid values: 00h-01h)
Negotiated
(valid values: 00h-01h)
Unchanged