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I'd like to capture packets on LVDS communications links. These links are a single pair in each direction - TX and RX, point-to-point, with 8b/10b encoding. I'm looking for options to sniff communications on these links to analyze packets for debug purposes. For most other communications links such as Ethernet, RS-232, I2C, USB etc - there are options to sniff communications on the wire or in a repeater or receiver. What about LVDS?

1 option is to modify an FPGA on 1 side of the link to buffer TX and RX traffic. This offers the advantage of gaining access to decoded data but this approach also has the disadvantage of modifying one of the components being debugged. It would be nice to be able to tap into a comm link and capture traffic.

Why would I do this? To debug communications problems caused by noise, hardware problems or bugs in code - the same reason that sniffers are used on other types of communications links.

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Are you pushing the link to its limits (data-rate, noise immunity etc)?

If not, can you just hang another FPGA LVDS pair off each of the TX/RX pairs? Use a high-end eval board, some simple code to dump the 1s and 0s into a buffer and then squirt them to a PC over Ethernet/USB/whatever for analysis.

I'm not aware of anything off-the-shelf for this (but I'd also like to hear if there is :)

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  • \$\begingroup\$ I would afraid signal reflections from the sniffing point... \$\endgroup\$ Sep 22, 2011 at 18:12
  • \$\begingroup\$ I don't think we're pushing limits - these are short 3" links - but to Bars's point, reflection might be an issue. Like Martin suggested, I'll look into using an eval board to sit in the chain and pass LVDS traffic through and internally 'T' or branch the data flow out an ethernet port. Such a device would also allow me to deliberately modify bits to see how the system handles CRC errors. \$\endgroup\$
    – JimFred
    Sep 22, 2011 at 20:50
  • \$\begingroup\$ @BarsMonster: me too, hence the opening question :) \$\endgroup\$ Sep 23, 2011 at 11:01

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