[USRP-users] Replacing DSP in N2x0

Ian Buckley ianb at ionconcepts.com
Tue Feb 14 15:50:47 EST 2012

Yes, there are commercial users of the USRP H/W who have swapped some or all of the signal processing H/W out for something custom, generally because they want to do something unusual and very specific for their application. I'm not personally aware of anyone having done what you suggest (swap out the CORDIC for another DDFS implementation), but it would be a relatively easy  task as that portion of the design is largely simple streaming data and an uber simple 32bit bus used to program the various registers that program the DDC frequency etc. The only consequence to the system as a whole I can think of off hand is that you might change the number of DSPCLK cycles of latency between an "off-air signal" being sampled and it being time stamped in the downstream vita logic, and that you might need to modify firmware so that the appropriate frequency value is programmed for your own DDC implantation.

Perhaps as a first you should simulate the CORDIC in isolation with test data and compare that with a reference model and/or alternate DDFS implementation such as a lookup table as a first step to establish if your supposition is correct? 

Removal of the TX DSP is trivial, track down dsp_core_tx, it contains most of the TX data path and comment it out...you should probably tie the strobe signal passing upstream to the vita logic.


On Feb 14, 2012, at 12:14 PM, Wilson, Jeffery (DS-1) wrote:

> Designation: Non-SSA/Finmeccanica
> Hello,
> I’ve been running some tests using an N200 (I also have an N210 at my disposal), and I’m a bit unhappy with the performance of the RX DSP (most likely the CORDIC itself). I wasn’t able to find much by searching the list archives or the web, but I was wondering if it is at all common for users to swap out the UHD implementation for a separate and/or proprietary IP core with better characteristics. Could anyone point me to any examples of this (if they exist)?
> I also remember seeing something at one time about removing the whole TX chain to make more room on the FPGA for RX-only applications, but haven’t been able to relocate it. I’d appreciate it if someone could point me to that info as well.
> Thanks,
> --
> Jeff Wilson
> Software Engineer
> DRS Signal Solutions, Inc.
> Direct: 301.944.8772
> 3.1.1001
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> USRP-users at lists.ettus.com
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