Open SCSI Integrator's Manual for NonStop S-Series Servers

Open SCSI Integrator’s Manual for NonStop Servers—422988-002
7-1
7
The SCSI SAC
The SCSI ServerNet addressable controller (SAC) is part of the PMF CRU, the IOMF
CRU, and the SCSI Plug-In Card (PIC) on the 6760 ServerNet/DA. The SCSI SACs
control the SCSI buses for the SCSI ports on these NonStop S-series CRUs.
This section describes the SCSI SACs on PMF CRUs, IOMF CRUs, and S-PICs on the
6760 ServerNet/DAs. It includes the following topics:
•
SCSI-2 Protocol Features Supported on page 7-1
•
SCSI SAC Bus-Phase Sequences on page 7-2
•
SCSI-2 Messages Supported on page 7-7
•
SCSI SAC Data-Transfer Modes on page 7-10
SCSI-2 Protocol Features Supported
With the exception of certain features and options listed in this subsection, the SCSI
SAC supports the SCSI-2 ANSI X3.131 - 1994 standard. All SCSI SAC bus-timing
characteristics (with the exception of fast SCSI, which is not supported) comply with the
SCSI-2 specification’s recommended values.
The SCSI SAC operates in a multiple-initiator and multiple-target SCSI bus
configuration with the SCSI SAC acting only as an initiator. Up to two SCSI SACs
(assigned SCSI IDs 6 and 7) are allowed on the SCSI bus. Either of these can operate as
an initiator. The SCSI SAC never operates in target mode.
SCSI-2 Features and Options Not Supported
The following SCSI-2 protocol features and options are not supported by the SCSI SAC:
•
Linked commands
•
Queued I/O
•
Asynchronous event notification (AEN)
The SCSI SAC does not check the SCSI command descriptor block (CDB). If the link
bit or flag bit is set in the control field of the CDB, SCSI operation might be
unpredictable.
SCSI-2 Messages
The SCSI SAC supports a subset of the SCSI-2 message system: the mandatory
messages plus certain optional messages are implemented. See SCSI-2 Messages
Supported on page 7-7.
Note. The SCSI SAC does not support SCSI-1 devices.