SPI-3 target-initiated negotiation changes

Robert Elliott relliott at hobbit.eng.hou.compaq.com
Fri Dec 10 07:58:34 PST 1999


* From the T10 Reflector (t10 at t10.org), posted by:
* relliott at hobbit.eng.hou.compaq.com (Robert Elliott)
*
During SPI-3 letter ballot resolution at the SPI working group meeting
in Rochester, we made this change:

(from the minutes 00-102r0):
  One significant change made was that when targets start a speed/width 
  re-negotiation (because they detect a change in the width and/or 
  synchronous data transfer rate). In this case, wide targets will be 
  required to send a WDTR message with a 00h transfer width exponent. 
  Narrow targets will be required to send an SDTR message with a 
  REQ/ACK offset of 00h. This will force the devices to use asynchonous 
  narrow transfers for the current I/O process. It is expected that the 
  initiator will, on the next I/O process, re-negotiate for the width 
  and speed settings it prefers.

An example of the new text is:
  If a target determines that the agreement is in an indeterminate state it
  shall initiate a negotiation to enter an asynchronous, eight-bit wide data
  transfer mode with all the protocol options bits set to set to zero. using
  a WDTR message with the transfer width exponent set to 00h.


I suggest we back off slightly, still requiring only WDTR and SDTR
to be used, but not requiring narrow asynchronous mode to be selected
with those messages.  Targets will still be barred from using PPR. 
Since WDTR and SDTR clear the IU, QAS, and DT protocol option bits 
and limit the transfer period, unsafe entry into DT DATA 
phases and use of rates that require domain validation 
testing will be prevented. 

This will keep most current target-initiated negotiation implementations
compliant.  I don't think targets are generating many PPRs yet.

This will also help keep performance up with legacy host software that 
will not reinitiate negotiation if the target gets reset.  Target-initiated
negotiation can be used to bring back Ultra 2 speeds.

New software that supports IU or QAS should also understand domain
validation and know how to renegotiate as needed.

Suggested wording:
  If a target determines that the agreement is in an indeterminate state it
  shall initiate negotiation using WDTR and/or SDTR as defined in x.x.x.x.


-- 
Rob Elliott      UNIX mailto:relliott at hobbit.eng.hou.compaq.com    
Houston, TX        PC mailto:Robert.Elliott at compaq.com
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