SPI Command IU CDB clarification

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Tue Sep 5 15:31:27 PDT 2000


* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*

The op code will be in byte 4. All of the CDB bytes are intended to be in
the same order as FC packets and parallel SCSI bytes in existing
implementations.

I'm not sure what your MSB/LSB confusion point is. Perhaps it is because
SCSI interprets these as Most Significant Bit and Least Significant Bit,
respectively, instead of Byte. Most significant bits are only valid within
a particular field or parameter and has no meaning across multiple fields.





"Day, Brian" <bday at lsil.com>@t10.org on 09/05/2000 04:08:57 PM

Sent by:  owner-t10 at t10.org


To:   "'t10 at t10.org'" <t10 at t10.org>
cc:

Subject:  SPI Command IU CDB clarification


* From the T10 Reflector (t10 at t10.org), posted by:
* "Day, Brian" <bday at lsil.com>
*

I've had another engineer interpret the CDB field differently than I had in
the SPI command IU CDB field.  The MSB/LSB notation was a little confusing.

The CDB field is defined at bytes 4 through 19 in the Command IU
(referencing Table 35 in SPI-3).  I've always thought the Operation Code
for
that CDB would be located byte 4, which would be the first byte of the CDB
to get transferred across the bus.  However, my colleague interpreted it to
be byte 19 because of the LSB notation.

As a specific example, if an initiator was sending a 10-byte WRITE command,
does the 0x2A come out on byte 4, or byte 19.

Can someone please clarify....

Brian Day
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