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?
Thanks,
Malihe
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
samples.
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).
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
_______________________________________________
Discuss-gnuradio mailing list
Discuss-gnuradio@gnu.org
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio