SAS-2: Physical link rate tolerance management QUESTION

Stephen FINCH steve.finch at st.com
Thu Jul 5 12:39:09 PDT 2007


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In section "7.3.2 Phys originating dwords", Table 115 lists the rate
tolerance insertion rate as:
"1,5 Gbps	   One deletable primitive within every 128 dwords
3 Gbps		   Two deletable primitives within every 256 dwords
6 Gbps		   Four deletable primitives within every 512 dwords"
My question:  
If an implementation inserts one deletable primitive every 128 dwords when
running at 3 Gbps or 6 Gbps, is that phy compliant or non-compliant with
this requirement?  
I can find no requirement that the two or four inserted deletable primitives
be consecutive.  If they are required to be consecutive, then I think the
standard should say so.
If they are not required to be consecutive, then why not just state "One
deletable primitive within every 128 dwords" for all speeds?  Or are we
purposefully allowing transmitting phys to hold off the insertions and then
do a burst?  To what advantage?  A disadvantage is the need for (a small)
amount of additional space in a speed matching FIFO if the distance between
deletable primitives can be 508 dwords (at 6G).
Steve Finch
STMicroelectronics



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