[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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 15:11:53 -0600
User-agent: Thunderbird (Windows/20100228)

Hi MArcus,
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, can I get those occasional programming instructions you mentioned to be hard-coded (for example changing the firmware so that it uses some default values instead of passing those values through GiGe) if I am interested in removing Ethernet and using debug bus to pass stream of data to the FPGA?
Marcus D. Leech wrote:
On 09/02/2010 02:48 PM, Malihe Ahmadi wrote:
I need 5 mega bit per sec of bandwidth and if I understand correct the rate of CMII_TX_CLK is 100 mega bit per second which is higher than what I want. The first reason I don't like GiGe is that it chunks the data and it can cause delay in its stream (I rather have my own protocol to transmit data to the FPGA) but I think I can bear with that! The second reason is that I don't know what is the relation between the stream of data generated at the source (for example by sig_source_i()) and the "GMII_TXD" input signal to the FPGA and eventually "sample_tx" input of dsp_core_tx. Can somebody explain that relation for me? Also, does anybody 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?


The rate that data is actually sent over the GiGe depends on your decimation/interpolation settings.

The FPGA "sees" a continuous stream of numbers that represent a signal, generally sinusoidal in nature. That "stream" is a complex-baseband representation of your signal, which the FPGA will interpolate, possibly digitally upconvert, and present to the RF transmitter hardware. Similarly on receive the FPGA gathers the complex baseband data from the A/D, decimates and filters it, and presents it to the GiGe interface for transmission to the host as complex baseband

I think you may be confusing the data rate of whatever modulation scheme you want to use in your application, with the rate that the *waveform data* is presented into/out-of your
  Gnu Radio flow-graph.

The packetization is generally not an issue, unless you are running at the "edge" where the host computer can't keep up, which produces overruns on receive, and under-runs on transmit.

But for modest-bandwidth signals, with a decent CPU, this doesn't happen very often.

The GiGe interface is simply a convenient and relatively-cheap way of getting complex-baseband data into/out-of the FPGA (along with the occasional programming instructions for the
  PLL synthesizers, gain controls, etc, on the daughter-cards).

reply via email to

[Prev in Thread] Current Thread [Next in Thread]