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?
Thanks,
Malihe
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?
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).
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