What are you actually trying to do?  That's a 50Mbit sustained transfer 
rate if bit time is 20ns.  100Mbit if 10ns.  And 4 channels.  That's 
200-400Mbps. You're moving a *TON* of data even at slower clock 
rates--there is no resource on the BBB that can keep that up very long.

This seems quite questionable on the BBB ... even moreso if your timing 
diagram is valid (which I suspect it is not).

First, given your diagram, the sampling point would have to be recovered.  
Note that the Clock, Data, and Frame are all coincident.  Normally the 
clock falls in the middle of the data window.  That's not easy to recover 
without a PLL.  I doubt the BBB has enough resolution to hit the data 
stable point on the data with any reliability at 50MHz.

Second, are you *actually* running at 50MHz?  Are you considering every 
*cross* as the frequency (high-to-low on a single line) or are you 
considering an individual signal rise-to-rise as the frequency.  Is that 
data changing every 20ns or every *10ns*?  If it's 10ns, it's probably not 
possible.

I would *STRONGLY* recommend that you use an FPGA.  Even an incredibly 
cheap FPGA would deserialize that with ease and then you could put it into 
a form in which you might be able abuse something like the RMII from the 
Ethernet peripheral to transfer it out.

But it's still a *LOT* of data.  You need something that can handle gigabit 
speeds if you keep this up even for a couple milliseconds.

Your best bet would be to use that FPGA to also decimate the data as well 
so that you're working with a reasonable amount of data.

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