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Re: [Discuss-gnuradio] USRP2, is that possible to skip the Ethernet and

From: Malihe Ahmadi
Subject: Re: [Discuss-gnuradio] USRP2, is that possible to skip the Ethernet and pass data through general purpose (physically accessible) inputs to the FPGA?
Date: Thu, 02 Sep 2010 14:19:54 -0600
User-agent: Thunderbird (Windows/20100228)

Hi Nick,
Actually we are using the USRP2 not for a SDR application, but we are using it to test our physical layer asynchronous backet based communication. For that I have to change the FPGA code and remove the interpolation/decimation and replace it with a spreading scheme. for that I need to know exactly what is the nature of data I am receiving at the FPGA and what is its maximum rate or forget about Ethernet and get a separate bus for me to pass the data to the FPGA . Assuming I want to use Ethernet, let's say I want to send the stream '0100001', and I pick DBPSK as the modulation. can you please explain what is the relation of the DBPSK modulated data and "GMII_RXD" input to the FPGA or "sample" input to the dsp_core_tx? is that FPGA receives 8 bits per symbol sent over Ethernet? Also, do you have a ready to use Python code for USRP2 device which generates for example a SIN wave at the transmitter and captures it at the receives?

Nick Foster wrote:

The USRP2 drivers are designed to abstract the user from the device transport, and in normal use you shouldn't have to concern yourself with the transport layer at all. You provide a stream of data in gnuradio, and the USRP2 provides a stream of data out the device (or vice versa). All the magic that happens between should be transparent. To the user, there is no packetization at all on transmitted data -- discrete Ethernet data packets are buffered in the USRP2 and transmitted seamlessly by the device.

If you are seeing "gaps" in signal when viewed on a scope, you are probably experiencing buffer underruns caused by running at a data rate too fast for your CPU to handle.

Can you explain the problem you are seeing with your device?


> Date: Wed, 1 Sep 2010 19:07:26 -0600
> From: address@hidden
> To: address@hidden
> Subject: [Discuss-gnuradio] USRP2, is that possible to skip the Ethernet and pass data through general purpose (physically accessible) inputs to the FPGA?
> Hi,
> I am using USRP2+RFX2400 board and trying to adapt our packetized
> communication on the board. As I understand the Ethernet does its own
> packetization on information data and we don't like that. therefore we
> are looking into avoid passing our information data to the board through
> Ethernet. We are also fine to make the configuration values for other
> peripherals on the board (such as DAC, ADC and daughter boards) fixed so
> that we still can get away with no Ethernet interface. so we are
> interested to know if there is a general purpose input bus (at least 5
> pins) that I can use to pass my data serially to the FPGA. That means I
> would like to see if it is possible to remove all the Verilog codes in
> FPGA related to handling the Ethernet interface and get the data I'd
> like to process through a general purpose input bus (at least 5 pins for
> clock and serial data input and 3 handshaking signals) instead of
> Ethernet port. For that reason, I need this general purpose bus to be
> physically accessible on the board so that I can connect them to a
> digital signal generator. Do you have any suggestion/recommendation for me?
> Thanks,
> Malihe
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> Discuss-gnuradio mailing list
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> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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