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Re: [Discuss-gnuradio] GPIO Rx Streaming

From: Tim Pearce
Subject: Re: [Discuss-gnuradio] GPIO Rx Streaming
Date: Wed, 23 Jun 2010 13:37:52 +0100


> Do I understand correctly that this is similar to gr-gpio? I thought
> VRT allowed separate streams, why are the bits still in the LSB of I
> and Q? Does this also work with UHD?

I'm using pre-UHD/VRT code at the moment - my understanding is the metadata VRT adds applies to a group of samples, the GPIO streaming lets you get boolean values associated with specific samples (with some fixed delay) - I was planning to use it to get a PPS into the PC before realising I could just use timestamps..

> How about dual DDC? Any news about dual DDC for usrp2? How easy would
> it be to add this to UHD?

I was looking into getting two IF streams as I and Q data a few weeks ago - there is a version of the USRP2 firmware which supports 2 DDC's - I think it uses slightly different filters - in the USRP2 FPGA code its under top/u2_rev3_2rx_iad. A mailing list post suggests the Makefiles need updating to use the new Ethernet code so its probably not suitable for UHD yet.

In case its helpful to anyone, the quick solution I went for here (given I'm still struggling to get an old version of Xilinx ISE) was to modify the firmware to set the BasicRX as a quadrature board and tuning to 0, which disables the CORDIC bit. This gives you two streams of IF if your happy with both streams being the same sample rate/untuned.


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