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Re: [Discuss-gnuradio] USRP mux configuration bug

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] USRP mux configuration bug
Date: Fri, 20 Jul 2007 17:13:12 -0700
User-agent: Mutt/1.5.9i

On Fri, Jul 20, 2007 at 05:02:55PM -0500, Ketan Mandke wrote:
> I have been experiencing a weird bug when transmitting packets using the
> USRP. I am part of the Hydra group at UT (hydra.ece.utexas.edu). We have
> been developing a multiple antenna system using the USRP. It seems to work
> quite well except for the following bug:
> Since we're using two transmit chains, I set the mux value in usrp.sink_c to
> 0xBA98. I have noticed however, that at random the transmitter will flip the
> IQ channels of the transmitter. I have verified that this occurs by
> analyzing the trace of the received signal. I noticed that this same bug
> seems to occur when using a single antenna system as well (there I set the
> mux value to 0x0098). In the single antenna case I can just reset the mux
> value to 0x0098 everytime I send a packet in order to alleviate the problem.
> This same approach does not work in the two-antenna case.
> Any thoughts on why the mux value in the transmitter might be changing or
> why the IQ channels might get flipped? Please note that I have already
> verified that the EXACT same waveform is being sent to the usrp everytime I
> transmit a packet; hence, I am certain that the bug is not being caused in
> software.
> I am currently using a multiple antenna system, so I set the usrp.sink_c mux
> value to 0xBA98. This should enable the USRP to support to transmit RF
> chains, right?
> -- 
> Ketan Mandke

Are you running one of our standard fpga images, or are you using one
that you have modified?  That is, are you writing verilog code?

If you are compiling your own verilog, are all timing constraints
being met?  Did you start with our project file?

It's seriously unlikely that the contents of the mux register is
getting randomly disturbed.


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