Negotiation Question: Wide or not?

Kendall, Guy gkendall at lsil.com
Thu Aug 15 13:40:13 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Kendall, Guy" <gkendall at lsil.com>
*
After the following PPR negotiation sequence, should the agreed bus width be
8 or 16 bits?

Initiator PPR OUT:
01 - Extended Message
06 - Extended Message Length
04 - PPR
09 - Transfer Period Factor
00 - Reserved
04 - Offset
01 - Transfer Width = 16 bit bus
02 - DT_REQ = TRUE

Target PPR IN:
01 - Extended Message
06 - Extended Message Length
04 - PPR
09 - Transfer Period Factor
00 - Reserved
00 - Offset = 0 => Asynchronous
01 - Transfer Width = 16 bit bus
00 - All options FALSE

In SPI-3 revision 14 (available on www.t10.org), page 157, Table 56 has the
following text:

The Target's PPR Response column says: "protocol options equal to 0h and
transfer period factor equal to 9h". Next to it the Implied Agreement column
says "Eight-bit/asynchronous data transfer with PROTOCOL OPTIONS field set
to 0h". In SPI-3, "protocol options" is defined as IU_REQ, DT_REQ, and
QAS_REQ.

I think I remember also seeing this statement in earlier versions of SPI-4,
but I can't find it anywhere in the current version. Perhaps it was removed
as part of the negotiation re-write.

Since the target sends back a Transfer Width of 16-bits, it makes sense that
the agreement should be 16-bit. However, if you follow that statement from
SPI-3, the agreement should be 8-bit.

Does anyone know what was meant by that statement in SPI-3? Was it correct?
Should the device really go to NARROW? Is this still true in SPI-4? If so,
can you direct me to where in the specification this situation is addressed?

Thanks,
Guy Kendall


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