[SI-LIST] SPI 4-2 question(s)


        Hello SI gurus:

It's my understanding that SPI 4-2 has Dynamic Phase Alignment (DPA) =
that basically centers the RDCLK in the middle of the RDAT eye opening - =
individually for each of the 16 data bits. Thus, usual =
source-synchronous timing measurements of Tsu/Thd become irrelevant for =
SPI4-2. What matters now is the eye opening - both vertical and =
horizontal.=20

Q1: Is there a eye mask defined for SPI4-2 industry wide? Or does each =
vendor have its own definition?

With the DPA in play, what is the response time of this de-skewing ckt? =
Here is why I am asking: the long term jitter, or long term closing of =
the eye does not matter any more. It's the short term jitter that =
matters.=20

Q2: What is the response time of the de-skewing mechanism? Is de-skewing =
done on the receiving end only, or can the launch time at the drives end =
be DPA'ed?

As I understand it, there is a training sequence sent frequently during =
initial power up. As the chip warms up and stops drifting, the training =
is sent less frequently and is controlled by the software. (Correct? Is =
this standard or vendor specific?) =20

Q3: Does the time interval between consecutive trainings depend on =
specific application? Does the de-skewing mechanism wait until parity =
errors are detected before sending the next training pattern. What is =
the meaningful timing measurement methodology for SPI4-2 simulations?

Q4: The previous level of SPI4, before SPI4-2 (what was its name?): does =
it exist only as a spec, or has there been silicon sampled? Is SPI4-2 =
backward compatible

Thanks in advance for offering your insights.

-Vadim Heyfitch
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