SAS - OOB detection
Elliott, Robert (Server Storage)
Elliott at hp.com
Sat May 24 08:23:54 PDT 2003
* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Server Storage)" <Elliott at hp.com>
> * From the T10 Reflector (t10 at t10.org), posted by:
> * Larrie Carr <Larrie_Carr at pmc-sierra.com>
> In Figure 58 - OOB Signal Detection of the SAS specification
> (originally Figure 47), there was a change between sas-r3f
> and sas-r3g of when an OOB event was detected. The original
> version in sas-r3f agrees with my interpretation of the SATA
> specification while the new version does not.
> SATA 1.0a states in section 6.7.4
> "OOB signals are observed by detecting the temporal spacing
> between adjacent bursts of activity, on the differential pair."
> The "temporal spacing" is the idle period and the "bursts of
> activity" is the ALIGN burst. Due to this statement and the
> min/max specification for the idle periods, I would expect
> the OOB receiver to process the idle periods only. Also, the
> requirement on an illegal idle time invalidating the event
> detection implies the ALIGN burst time is not important.
> With this intent, the logical place to declare an OOB event
> (such as COMSAS) is at the end of a OOB idle period just
> after the ALIGN burst is detected.
> With the current definition, it appears you may have to
> measure the ALIGN burst (which we don't have any
> specifications for) and then declare the OOB event when you
> just get the beginning of the next OOB idle period. However,
> this declaration does not take into account the length of the
> OOB idle period (suggesting that any idle is valid).
> A strange side effect of the sas-r3g specification is that an
> OOB event detection is trigger at the beginning of the OOB
> idle period which is the OOB event negation.
> Can someone please add some color on this change?
The same logic should work for both SATA and SAS. SAS is
just pickier about how it specifies things - including a
token minimum burst time of 100 ns and saying that the
repeating pattern is "idle/burst" rather than "burst/idle".
The key is to measure 4 idles of the proper length (and
not be fooled if the first or last idle is too long).
You can't do that without seeing a burst after the 4th
> Larrie Carr
> Principal Engineer
> PMC-Sierra, Inc.
> 8555 Baxter Place, Burnaby, BC, Canada V5A 4V7
Rob Elliott, elliott at hp.com
Hewlett-Packard Industry Standard Server Storage Advanced Technology
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