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[Discuss-gnuradio] FPGA Modifications for a Continuous Carrier?

From: Michael P Buettner
Subject: [Discuss-gnuradio] FPGA Modifications for a Continuous Carrier?
Date: Tue, 24 Jul 2007 10:31:37 -0700 (PDT)

Hello folks.  I am currently looking at using the USRP for interaction with RFID 
tags. The crux of the problem is that I need to transmit a continuous carrier wave 
to power the tag, but I also need very low latency with respect to receiving a tag 
signal and responding to that signal (< 500us.  Not going to happen, but the 
closer the better). Currently, I am transmitting the carrier from the host which 
eats up half of my USB bandwidth and keeps the TX buffers full, both of which are 
killing my latency.

  My question is, would it be possible to modify the FPGA so that the default behavior is 
to transmit the carrier until it receives buffers for transmit? This should reduce the 
latency by using the USB half duplex, keeping the TX buffers empty which allows for burst 
transmits, and also by freeing up some computes which are now burned sending out 

  To further complicate the problem, I've very little experience working with 
FPGAs and verilog.  So, a caveat to the above question is that this not only 
needs to be possible, it needs to be relatively straight forward as well.

  Any advice as to the feasibility of this endeavor would be greatly 
appreciated. If it seems reasonable, pointers as to what would be involved, 
where I would need to look, etc. would also be helpful.  Thanks.

   Michael Buettner

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