Re: [Discuss-gnuradio] Serial io questions

[Brian Padalino]

On Thu, Aug 14, 2008 at 3:01 PM, Sebastiaan Heunis <address@hidden> wrote:
> Hi
>
> If have a few questions regarding the serial interface between the FX2
> and the FPGA and the writing of registers.  I would just like to know
> how serial_strobe, serial_data and serial_addr signals work?  I know
> that serial_io.v handles this and generates a strobe to tell the
> modules that something was written on the serial interface.
>
> I would just like to know how these signals work.  When does
> serial_strobe go up and how is serial_data and serial_addr stored?
> For now I want to write a testbench for phase_acc.v.  I would like to
> know how the serial input to this module should look in order to input
> the address and a frequency value into this module and get it to
> output freq.  I want to then see what the phase output that goes to
> cordic.v looks like in order to simulate cordic.v.
>
> setting_reg #(FREQADDR)
> sr_rxfreq0(.clock(clk),.reset(1'b0),.strobe(serial_strobe),.addr(serial_addr),.in(serial_data),.out(freq));

At the top is just a SPI interface.  Reference the timing here:

    http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus

The serial interface is decoded using serial_io.v found here:

    
http://gnuradio.org/trac/browser/gnuradio/trunk/usrp/fpga/sdr_lib/serial_io.v

This decodes the address and data that is written to the register and
strobes the valid signal to all setting registers.  Reading
setting_reg.v here:

    
http://gnuradio.org/trac/browser/gnuradio/trunk/usrp/fpga/sdr_lib/setting_reg.v

If the address of the module matches the address that was written to
serial_io.v, this will latch the data and output a single pulse
'changed' to signal the data has changed.

To simulate - just set the address and data values appropriately,
strobe, and go.  The setting_reg will latch the values in and
everything should work properly.

Hope this helps.

Brian