Data field size of intermediate data groups

Bill Galloway BillG at breatech.com
Wed Mar 3 11:49:12 PST 1999


* From the T10 Reflector (t10 at symbios.com), posted by:
* "Bill Galloway" <BillG at breatech.com>
*
Bob,

I do not look forward to supporting this either but I think we have to.  Any
device that does not have a multiple of four block size could get into trouble.
I could imagine a tape drive that wants/needs to do a CRC every block. If the
block size was not a multiple of four then they would violate your rule.  Also
not all disk are formatted for 512 bytes, I know of some that are formatted for
514. This disk could get into trouble with intermediate CRCs as well.

Bill Galloway
BREA Technologies, Inc.
P: (281) 530-3063
F: (281) 988-0358
BillG at breatech.com

-----Original Message-----
From: owner-t10 at Symbios.COM [mailto:owner-t10 at Symbios.COM]On Behalf Of
Robert Frey
Sent: Wednesday, March 03, 1999 1:34 PM
To: t10 at Symbios.COM
Subject: Data field size of intermediate data groups


* From the T10 Reflector (t10 at symbios.com), posted by:
* bobf at advansys.com (Robert Frey)
*
There seems to be a simplifying restriction, which may be common
practice, about the size of data fields in intermedidate data groups,
i.e. data groups that do not end a DT DATA IN or DT DATA OUT phase.
If the data fields in such intermediate data groups all are required
to have modulo 4 size, at least some implementations would benefit
|from reduced logic cost and improved performance. In other words only
the last data group in a DT PHASE would ever contain a (0 or 2 byte)
pad field.

Can any reasons be put forth for why such a requirement on the data
field size of intermediate data groups is undesirable? If not I will
write a proposal for future consideration.

SPI-3 Rev. 2:
> 8.2.2.3 Data group format
>
> Each DT DATA IN phase and DT DATA OUT phase contains one or more data groups.
> A data group consists of a data field followd by a pad field, and then
> followed by a CRC field. The number of bytes transferred within a data
> group shall always be even and a multiple of four.

Bob Frey
bobf at advansys.com
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