SAS - OOB detection

Larrie Carr Larrie_Carr at
Fri May 23 17:34:31 PDT 2003

* 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?

Larrie Carr

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

Cell: 604.839.9532
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