
SCSI Functional Description
2-23
2.2.5 Designing an Ultra3 SCSI System
Software modifications are needed to take advantage of the Ultra3 speed
in the SYM53C1010. Since Ultra3 SCSI is based on existing SCSI
standards, it can use existing drivers if they are able to negotiate for
Ultra3 synchronous transfer rates. Also, the target device must be able
to communicate at Ultra3 speed. The SYM53C1010 uses Domain
Validation to determine whether or not the system is capable of Ultra3
SCSI before activating DT clocking. Refer to
Section 2.2.5.1, “Ultra160
SCSI Features,”
for more information on DT clocking.
LVD SCSI fulfills the hardware requirements for Ultra3 SCSI transfer
rates, increased cable lengths, and additional devices on the bus. All
devices on the bus must have LVD SCSI capabilities to guarantee Ultra3
SCSI transfer rates. For additional information on Ultra3 SCSI, refer to
the SCSI Parallel Interface-3 (SPI-3) working document that is available
on the world wide web at the T10 Home Page, http://www.t10.org. Also,
check the SCSI Trade Association web site at http://www.scsita.org/.
Chapter 6, “Specifications”
contains Ultra3 SCSI timing information. In
addition to the guidelines in the draft standard, make the following
software adjustments to accommodate Ultra3 SCSI transfers.
2.2.5.1 Ultra160 SCSI Features
Domain Validation –
A procedure where a host queries a device to
determine its ability to communicate at the negotiated Ultra3 data rate.
In software, the following steps are performed to ensure the selected
device can successfully transfer data at the negotiated speed.
Step 1.
Select a device.
Step 2.
Issue Inquiry command.
Step 3.
Issue Parallel Protocol Request (PPR) message.
Step 4.
Issue Write Buffer command.
Step 5.
Issue Read Buffer command.
Step 6.
Examine the data pattern to ensure validity.
If the commands complete successfully with no CRC errors, bus hangs,
or data pattern errors, then the negotiated speed is valid.