Re: [Discuss-gnuradio] Simple signal echo with the USRP

[sravya reddy]

hi,
i am also trying to modify the verilog code in usrp fpga. mail me if you
have hello world program to do that. I am not understanding how to do it
exactly.
thanks in advance.


Balijepalli, Arvind wrote:
> 
> I am starting to look into building a feedback controller, which takes the
> position of the particle and outputs a suitable control signal. The
> controller itself will most likely be a tabulated function, which we can
> implement using a lookup table. However, I am having trouble getting a
> basic signal echo going. I have installed GNU radio as well as the Quartus
> compiler and worked through compiling and running the top level std_usrp
> project. 
> 
> As a next step, I am trying to modify the USRP FPGA Verilog code to build
> a simple signal echo. The Verilog code is extremely simple in this case. I
> started by modifying to top level usrp_std.v and simply mapped the input
> rx_a_a and rx_b_a onto tx_a and tx_b, cutting out all the other extraneous
> code pertaining to the USB. The essence of the Verilog code is: Create two
> registers to drive the output wires and echo the output at the positive
> edge of the clock. This code compiles without errors in Quartus (although
> this doesn't necessarily imply that it should work).
> 
>       reg lTXA;
>       reg lTXB;       
> 
>       assign      tx_a  = lTXA;
>       assign      tx_b  = lTXB;
> 
>       always @(posedge clk64)
>       begin
>                lTXA = rx_a_a;
>                lTXB = rx_b_a;
>       end
> 
> 
> However, I am not sure how to setup the python code to get this to
> successfully run. The code snippet below doesn't seem to do the trick.
> 
> 
>       src = usrp.source_c(which=0, decim_rate=64, nchan=2, mode=0,
> fpga_filename="echo.rbf")
>       dst = usrp.sink_c(which=0, nchan=2)
> 
>       self.connect (src, dst)
> 
> Can someone point me in the right direction with this? Also, I haven't
> found a simple "hello, world!" example to modify the FPGA code. Does such
> an example exist? If it doesn't, I will be happy to get this to a point
> where it is usable and submit it back to the community. I think it may be
> useful for others like myself who are new to Verilog/FPGAs and may provide
> an easier entry point to start modifying the FPGA code.
> 
> 
> Thanks,
> Arvind
> --
> Arvind Balijepalli
> 
> NIST
> 100 Bureau Drive, Mail Stop 8212
> Gaithersburg, MD 20899 
> 
> 
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> 
> 

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