08-23-2016 12:16 AM
08-15-2016 10:01 PM
check this ARs
PPM is an inaccuracy of certain components (quartz crystal in case of clock generator) in a circuit which leads to generation of a signal with inaccurate period. PPM does not break the periodicity of a signal. As its name states, PPM is a long term effect which denotes the inaccuracy in the bit period over a million clock cycles. PPM is additive or subtractive in nature.
Onlyif cumulative effect of jitter or PPM in TX CLK becomes more than half of RX CLK then there would be errors due to over/under sampling.
An example below shows how ongoing variations in incoming data stream can affect the sampling of data. This same example will be considered to resolve the issues as we progress further.
RX CLK(FD) is frequency locked during frequency detection. As the incoming data stream is being sampled on FD, as depicted in the red box, a single bit is getting sampled twice. This occurs because of the variations in the incoming data bit stream.
To encounter these variations in frequency of TX CLK, the second function of CDR, Phase alignment comes in picture. This readjusts RX CLK edges.
PPM should be in within the specified limit of device vendor
08-15-2016 10:26 PM
I understood the concept, but if protocol has ppm in range of +300 to -5300 ppm then is there any changes in wrapper generated parameters? like RXCDR_CFG? because there is not any value of RXCDR_CFG for +300 to -5300 ppm.
08-15-2016 10:32 PM
08-15-2016 10:57 PM
I have gone through it multiple times but not found any perfect information regarding values of RXCRD_CFG in case of +300 to -5300 ppm.
For your reference, SATA's setting for RXCRD_CFG which is generated by wrapper is also not listed in UG746.
//For SATA Gen3 GTX- set RXCDR_CFG=72'h03_8000_8BFF_1020_0010
So can you explain me how can you people derive that valuations?
08-15-2016 11:27 PM
These value suggested by silicon team and use need to use as it is as mention in UG
08-15-2016 11:30 PM
08-15-2016 11:35 PM - edited 08-15-2016 11:36 PM
For what protocol are you looking to use the CDR_CFG for? Most of the supported protocols for the CDR are either mentioned in the Product Guide, through Answer Records or through the protocol selection in the GUI(where the CDR value can be checked in the GT files). These are the only protocols for which we officially support for the CDR.
Here is one AR which points the recommended CDR values - http://xkb/Pages/51/51884.aspx
I assume the CDR cannot support PPM of -5300 but have to cross-check on this. Will get back.
08-15-2016 11:51 PM
Custom protocol like PCIe & SATA.
You can see the PCI_Express_Base_Specification_V20, where they have given base ppm of +/-300 and SSC of down spread of 0 to 5000 ppm. ultimately ppm in range of +300 to -5300 ppm.
SATA also has the range +350 to -5350 ppm.
08-16-2016 12:10 AM