Re: [Discuss-gnuradio] packets to the usrp and loopback

[Brian Padalino]

On 4/20/07, Thibaud Hottelier <address@hidden> wrote:
> Hi,
>
> I moved all my small testing blocks from ModelSim to the Quartus source
> tree. I am writing the glue code between the modules so we should have
> the basic Tx functionality working relatively soon. But before that, I
> would like to simulate to whole Tx block in ModelSim, so I need some
> information about how the tx_chains work.

There should be absolutely no glue logic between the modules within a
top entity possibly called mblock_processing.  The inputs should feed
the specialized USB FIFOs, and the outputs should feed the separate
CIC channel filters (complex).

Everything else from there should be straight forward with strobing
samples in and out.

> A what rate should I send the samples to the tx_chains? Every 4 clock
> cycles? They seems to be controlled by tx_strobe, but I failed to
> understand what this signal actually mean.

The minimum interpolation rate is 4 due to the CIC filter limitations,
so once every 4 will yield one side of the spectrum.  I believe 128 is
the other end of the spectrum, but you should set a constant for the
rate so we can test with different ones.

The tx_strobe happens once every rate clock cycles - with which it
will send in a new sample.  That strobe sends a new value down the TX
stream and reads a new one ready for the next tx_strobe.

> What is the point of the bus_reset and the clear_status signal? They are
> both input to current tx_buffer.

I am not sure of this - but I am assuming to stop/reset the transmit
path and clear any status messages respectively. :)  I'll try to have
a look at the code and find out more later.

> As we report overrun/underrun in packet header, are we gonna get rid of
> the tx_empty, have_space and tx_underrun signal ?

have_space is used by the feeding FX2 to know if the FPGA can handle
one more packet.  This signal shouldn't go anywhere.  The other
signals should probably stick around for now.

> Comments on the code I checked in are welcome...

I'll look it over this weekend and give comments and feedback.

Brian