SAS - OOB detection

Elliott, Robert (Server Storage) Elliott at
Sat May 24 08:23:54 PDT 2003

* From the T10 Reflector (t10 at, posted by:
* "Elliott, Robert (Server Storage)" <Elliott at>
> * From the T10 Reflector (t10 at, posted by:
> * Larrie Carr <Larrie_Carr at>
> 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

> Thanks,
> Larrie Carr
> Principal Engineer
> PMC-Sierra, Inc.
> 8555 Baxter Place, Burnaby, BC, Canada  V5A 4V7

Rob Elliott, elliott at
Hewlett-Packard Industry Standard Server Storage Advanced Technology

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