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[jmcgrath at qntm.com]

        Reply to:    


--------------------------------------
Date: 4/30/94 6:29 AM
To: Jim McGrath
From: ljlamers at aol.com@smtpgw
X-Mailer: America Online Mailer

4/30/94

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
clear.

jpm - I agree

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.

jpm - I agree - level 1 devices need not know about the level 2 world

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

I believe the answer is yes to insure backward
compatibility.

jpm - I agree

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
condition.

jpm - I agree

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.

jpm - the concept of a savable ID is orthongonal to SCAM -
we can discuss it as a regular SCSI work item.  The key is that
any savable ID must work as the defualt ID works, not the soft 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.

jpm - I agree

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.

jpm - no opinion

Regards,

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

jpm - boy, going to adaptec has made Larry more agreeable!