SCAM Questions

ljlamers at ljlamers at
Sat Apr 30 06:01:09 PDT 1994


TO:  X3T10 Membership
FR:  Larry Lamers
RE:  Comments on SCAM
DATE:     April 14, 1994

During the process of incorporating SCAM into SPI some
questions have arisen.

1)   Should legacy, level 1, and level 2 host devices be
allowed on the same bus?

I think that this is highly desireable.  If not, then level
2 host devices will find limited application.  Currently Rev
5 of SCAM prohibits this, but the justification is not

2)   Is a level 1 device required to recognize dominant
master contention?

This one is debateable, but I believe the answer is no.  Rev
5 of SCAM did not specifically require this.

3)   Is a level 2 device required to have a current ID?

I believe the answer is yes to insure backward

4)   Should the soft ID be saved to the saved ID to become
the current ID following the a subsequent reset condition or
power-on condition?

The answer seems to be no - the soft ID is never remembered
by a device following a reset condition or a power-on

5)   Is someone going to propose a mode page to set the
current/saved ID?

Many disk drives already support a vendor unique mode page
to set the SCSI ID.  The new SCSI ID becomes the saved ID
following a reset condition or a power-on condition if the
save parameters bit is set.  The current ID is determined by
first checking the non-volatile storage.  If a saved ID
other than zero exists then the saved ID becomes the current
ID.  If the saved ID is zero then the default ID set by the
jumpers/switches becomes the current ID.

The hard ID is the current ID of the device following a
power-on condition.

The soft ID becomes the current ID if a SCAM protocol occurs
and assigns a soft ID to the device.  The soft ID shall not
become the saved ID.

6)   Can we get rid of the abhorent terminology and used
SCSI terminology.

A SCAM master is really a SCAM initiator.  A SCAM slave is
really a SCAM target.

7)   Are all SCAM host adapters required to put out the bus
master contention code?

This has been a real debate - the document is ambiguous - or
rather seems to state both sides of the case - that a host
adapter at level one does not need to do bus master
contention but that all scam masters should do it.  There is
a potential interoperability problem here.


Lawrence J. Lamers
Adaptec                    TEL: 408-945-8600 ext 3214
691 Milpitas Bvld          FAX: 408-957-7193
Milpitas, CA   95035       EMAIL: LJLAMERS at ADAPTEC.COM

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