SAS-2 SNW final window TRAINDONE

[Alvin.Cox at seagate.com]

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I am posting this as a seed for reflector discussion. We are making great 
progress on the speed negotiation sequence and I would like to see things 
worked out for our meeting on September 12th. I believe we have the 
proposals in place, but we need some significant editing to make sure we 
cover the details and uncover the holes.
Per our discussion yesterday, there was much concern that the final speed 
negotiation window completion is not well-defined. I am concerned that 
this is an area of hardware impact, so we need to consider what is going 
on and how to make this robust.
How many TRAINDONE primitives should be sent at a time? The present 
proposal shows 4. It was mentioned that this is an arbitrary number and 
some suggested that there should be 6. How many are detected to 
acknowledge that the sequence is actually over? (Remember that this is not 
OOB bursts.)
The current proposal has two consecutive TRAINDONE sets around a scrambled 
data payload sent by both PHY's as completing the training sequence. What 
if the payload received after the first TRAINDONE is corrupt? Can the PHY 
transmitter switch back to the TRAIN primitive to get additional time 
since it saw an error in the data and may need additional training? I 
don't see anything preventing this, but I don't want the option 
overlooked.
Any other ideas? This window is significantly different from the other 
speed negotiation windows so let's think it through and share the thoughts 
so we can all think about them before our next call.
Alvin Cox
Seagate Technology, LLC
Tel 405-350-7424
Cell 405-206-4809