SAS lock time question

Brown, Russ Russ_Brown at
Mon Jul 8 11:09:52 PDT 2002

* From the T10 Reflector (t10 at, posted by:
* "Brown, Russ" <Russ_Brown at>
( Fig numbers etc refer to sas-r00c)

In for example Fig 37, SAS Speed Negotiation, between the different G1, G2,
etc rates, the time RCD=320ns max is allowed for transmitters to change
speed. This should be fine, as long as the different rates are simple
multiples and can be obtained from clock dividers without changing VCO

The receiver clock recovery circuits however could be stuck with a timing
loop settling issue. Suppose during the third speed negotiation window (G3)
in Fig 37, the far end device does transmit, but the received signal quality
is poor and pattern sync is not achieved.
Depending on the architecture used, the receiver clock recovery loop could
get lost and be pulled off-frequency, and then require a "lock to reference
clock" interval before it could successfully lock to the "negotiated G2
rate" in the final speed negotiation window.

Does the present SAS standard allow enough time to handle this situation?
The total time presently allowed for each speed negotiation window,
including the RCD=320ns max time, is 109.2 usec.

Russ Brown
Maxtor Corp
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