Negotiation Question: Wide or not?

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Fri Aug 16 07:05:49 PDT 2002


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

What SPI-3 says is: If the initiator asks for period = 9 and protocol
options = 0, this is an illegal combination. For an illegal combination
like this, the target is supposed to revert to asynchronous/ 8 bit wide.

The case you illustrate doesn't fit that situation. The initiator is
correctly asking for period = 9 and protocol options = 2 (DT_REQ set like
it has to be for this period).

I believe your case is caused becuase the target doesn't implement an
offset of 4 with the combination of period = 9 and options = 2. The target
probably requires a larger offset value to work at this period. Therefore
the target chooses to revert to asynchronous (rounding the offset to the
next lower implemented value). The width doesn't have to be rounded down in
this case as long as the target implements two byte wide operation.



                                                                                                  
                    "Kendall,                                                                     
                    Guy"                 To:     "'t10 at t10.org'" <t10 at t10.org>                    
                    <gkendall at lsi        cc:                                                      
                    l.com>               Subject:     Negotiation Question: Wide or not?          
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* 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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