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609 Views
Registered: ‎10-28-2019

What is the point of transceivers when FPGAs can't even receive data in the GHz range?

Hey all, I have been working on a project for some time now where the objective was to receive 5.6GB/s of data on 6 different lines into an FPGA using the GTX/GTH transceivers on the Virtex-7 VC7215. There is a clock synchronous with the data at 2.8GHz DDR. After many months of work, I have come to the conclusion that there is absolutely no way that any FPGA can handle this as the data is unencoded, NRZ, and no internal/external memory element could receive 5.6GB/s. With that being said, can anyone discuss what the transceivers are good for in terms of receiving data if at high speeds the FPGAs can't even support it?

 
5 Replies
Explorer
Explorer
591 Views
Registered: ‎04-19-2018

Re: What is the point of transceivers when FPGAs can't even receive data in the GHz range?

 

Maybe the word 'deserializer' brings some of the light you have been looking for in those months of work.

Typically, Gb transceivers are serial (one bit after other). Typically, data is deserialized and becomes a stream of 16, 32, 64, etc. bits and so the clock is divided as well. 

Yes, you are right that even a fast Virtex-7 -3 speed won't run IP cores much faster than 300 MHz, but 300 MHz x 64 bits = 19.2 Gbps. Voila. Does this make sense?

Scholar richardhead
Scholar
579 Views
Registered: ‎08-01-2012

Re: What is the point of transceivers when FPGAs can't even receive data in the GHz range?

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Teacher drjohnsmith
Teacher
568 Views
Registered: ‎07-09-2009

Re: What is the point of transceivers when FPGAs can't even receive data in the GHz range?

@namanjohnson101

you are dead right,
no one in there right mind would try and transfer any data between two chips at 5.6 GByte/s , over multiple lines, and rely upon a sysncronous clock to decode the data.

The timing of all the tracks would have to be amazingly correlated, I'd say probably past the ability of most board manufacturers,

The answer, was found many years ago, send data encoded with a clock embeded and make the data have zero DC content such that it can be AC coupled.
You add to that timing markers in the data, and FIFOs at each end, and data can with relative ease be sent at 50 + Gbit/s over multiple syncronised lines,
As used in 400 Gb ethernet or 100 Gb SDI video or 150 Mb/s Interlarken,

The fact your data is un encoded NRZ, and does not work does not surprise me.

The nearest to your requirement, is the special DDR memory interfaces built into the FPGAs , but these do not use the GTx transceivers, but the slower IO pins, and PLL in the DDR chips, burst data and constant tuning algorithms to work,

I note in your original post on 28th October, you did not go into the details of what you wanted to do, if you have I am certain some one would have pointed you at the problems,

What to do ?

Well the data , can you encode it so that the GTx requirements are meet ?

If not, you might be able to "over sample" the data and clock using the GTx, and then by a bunch of your own logic work out what the data was, Im think of something like this
https://www.xilinx.com/support/answers/34192.html

but its not going to be easy,

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
Tags (1)
Moderator
Moderator
396 Views
Registered: ‎11-09-2015

Re: What is the point of transceivers when FPGAs can't even receive data in the GHz range?


@richardhead wrote:

How about ethernet?

https://www.xilinx.com/support/documentation/ip_documentation/tri_mode_ethernet_mac/v9_0/pg051-tri-mode-eth-mac.pdf


And HDMI 2.0 (5.4 Gbps/lane), Displayport 1.4 (8.1 Gbps/lane), SMPTE-SDI...


Florent
Product Application Engineer - Xilinx Technical Support EMEA
**~ Don't forget to reply, give kudos, and accept as solution.~**
Guide avrumw
Guide
255 Views
Registered: ‎01-23-2009

Re: What is the point of transceivers when FPGAs can't even receive data in the GHz range?

..., USB, SPI, Thunderbolt, SATA, PCIe, ...

And dozens and dozens of other protocols.

Clock/data recovery techniques are REALLY old - 8b10b encoding was developed in the 1980s.

Avrum