PPR/MESSAGE REJECT implied agreement

Elliott, Robert (Hou) Robert.Elliott at COMPAQ.com
Thu Aug 31 14:23:08 PDT 2000


* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Hou)" <Robert.Elliott at compaq.com>
*
There is a problem in the PPR description in SPI-3 and SPI-4.  
See SPI-4 revision 0 page 198.

Table 58: PPR messages implied agreements
Target's PPR response:
	MESSAGE REJECT message 
Implied agreement:
	The initiator shall set eight-bit/asynchronous
      transfer with protocol options field set to 0h

If an Ultra 3 initiator has an WDTR/SDTR negotiation in effect
with an Ultra 2 target, the target will issue a MESSAGE REJECT
to an incoming PPR OUT because it doesn't understand that message.
The target will maintain its current negotiated settings.  The
initiator should do the same, rather than drop down to
eight-bit/async mode.  Otherwise, the data phase won't work.
The target may start streaming REQs while the initiator is
expecting only one.

We believe this is how most SPI-3 devices behave anyway.

Suggested correction:
    The initiator shall retain its previous data transfer
    mode and protocol options

I'll create a document for the September Parallel SCSI WG
meeting proposing this change.
---
Robert.Elliott at compaq.com
Compaq Server Storage Advanced Technology

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