Async CRC issues

Jeffrey L Williams Jeffrey.L.Williams at wdc.com
Wed Apr 21 17:30:09 PDT 1999


* From the T10 Reflector (t10 at symbios.com), posted by:
* Jeffrey L Williams <Jeffrey.L.Williams at wdc.com>
*

I just read the Async CRC proposal and I have a few issues I would like
discussed at the next working group meeting.

1.  The error handling for ACRC errors listed in 119r3 states that a Check
Condition is returned on an error in the message out or command phases.  I
recall at a working group meeting much earlier, where we had agreed to
change this to state that the error handling would be handled the same way
it is handled for parity errors.  In fact, we would state that these
errors were handled "as defined in the section on parity errors" or some
words to that effect.  The issue I had was that it is much less disruptive
to existing code to take this error interrupt exactly as a parity error
today (which this in effect is) and handle it in the same way.  The
working group agreed with that approach to the best of my recollection.

2.  The section on enabling the checking appears to be problematic to me. 
Specifically, if parity is correct but there are ACRC errors, the device
should disable checking.  It seems as though this leaves errors
undetected.  For example, a target transferring status and command
complete with high bus errors (all zeros) would be allowed to complete the
IO and not be told of the error.  I believe the ACRC should be a
negotiated value added to the PPR message.  This makes the checking
unambiguous.  The only hole is that messaging is used to turn on all
future messaging ACRC checks.  I think this argument is not very strong. 
If you can't make it through the few messages to set ACRC and other PPR
parameters, nothing is going to work on this bus, including domain
validation.

John Lohmeyer, can we add 119r3 back onto the working group discussion to
address these issues.  I noticed that in the WG minutes from April 7 this
was a point of contention and the vote was close, so I think it bears
further examination.





Regards,
Jeff

Jeffrey L. Williams
Senior Staff Engineer
Western Digital Rochester -Enterprise Storage Group
Office: (507) 286-7589
Fax: (507) 536-8089
Pager: (888) 858-PAGE   ID: 120826
e-mail: Jeffrey.L.Williams at wdc.com

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