SAS Phy layer _ some queries

Elliott, Robert (Server Storage) elliott at
Sun Oct 3 09:38:59 PDT 2004

* From the T10 Reflector (t10 at, posted by:
* "Elliott, Robert (Server Storage)" <elliott at>
> * From the T10 Reflector (t10 at
> posted by: Jim Lott <Jim.Lott at> *
> SAS1.1r5 section 6.5, with regard to oob states:
> "A receiver shall detect an OOB signal after receiving four
> consecutive idle time/burst time pairs (see figure 58). It
> is not an error to receive more than four idle time/burst
> time pairs. A receiver shall not detect the same OOB signal
> again until it has detected the corresponding negation time
> (i.e., a COMINIT negation time for a COMINIT) or has
> detected a different OOB signal (e.g., if a COMINIT was
> previously detected, then four sets of COMWAKE idle times
> followed by burst times are detected, a COMWAKE is
> detected; another COMINIT may follow)."
> Scenario:
> Let's assume that as many as 100 COMINIT burst idle pairs
> are received without the negation at the end. The burst
> idle pairs are changed to an invalid OOB or a different OOB
> signal at some point within the 100 pair. COMINIT detected
> is sent to the SP state machine after 4 consecutive valid
> pairs are received.
> Question:
> What happens after the invalid sequence (or a different OOB
> signal) is received?
> The COMINIT has been detected and the OOB sequence changes
> Does the COMINIT detected remain valid?

In the standard (unlike in real hardware), all the messages are
edge-based, not level-based.  The COMINIT Detected message is only true
the first time the condition is detected.  Sometimes the standard will
say a message is "repeatedly sent" when it needs level-based semantics.
I don't think that is necessary within SP for handling these messages.

> > Should COMWAKE detected become valid after detecting 4 
> COMWAKE sequences?


> > Should the COMINIT be considered completed upon detection 
> > of the COMWAKES or the fact that valid COMINITs are no 
> > longer being received?

COMINIT Completed occurs only if a valid COMINIT negation time is
detected.  As Henry Wong said, you can have COMINIT Detected followed by
COMWAKE Detected without an intervening COMINIT Completed.

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

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