SAS: OOB Timing Tolerances

Neil Wanamaker neil.wanamaker at finisar.com
Wed Feb 9 11:46:37 PST 2005


* From the T10 Reflector (t10 at t10.org), posted by:
* "Neil Wanamaker" <neil.wanamaker at finisar.com>
*
SATA specifies requirements on both the transmitter and receiver for
tolerances in duration, i.e., 
for COMINIT the transmitter idle time shall be  310.4 to 329.6 ns and
the receiver must detect 
COMINIT if the spacing is between 304 and 336 ns.

SAS has the same requirements for the receiver, but the only
specification for the transmitter is that
the idle time for COMINIT must be 480 OOBIs, where an OOBI may vary from
666.6 - 666.733 ps; this
translates to an idle time between 319.968 ns and 320.031 ns. Given that
this is a small fraction of a
unit interval, I would expect that the actual timing is subject to
things like cable capacitance, board
trace lengths, etc.

Given that the receiver tolerances must allow for SATA devices, the
present spec is both
unnecessarily restrictive and unmeasurable.  I'd like to propose that
SAS spec the same transmitter 
tolerances on out-of-band signals as SATA, with a comparable variation
allowable for COMSAS. 

Neil Wanamaker
neil.wanamaker at finisar.com
512.670.7303 (O)


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