Re: [Discuss-gnuradio] tx mux explained!

[cswiger]

On Fri, 26 Aug 2005, Eric Blossom wrote:

> It would take some work, and you'd also need to build the DUC in the
> FPGA.  We have tested the FPGA based DUC in the (distant) past, and as
> you may have noticed, there is #ifdef'd code in the host library to
> deal with it.
>

That was my mis-conception: there are two interpolators in the FPGA
which can be mux'd about but there is one DUC in each 9862, not
the fpga, for the two outputs.

This can be checked:

>>> from gnuradio import usrp
>>> sink = usrp.sink_c(0,64)
>>> sink.set_tx_freq(5e6)
>>> hex(sink._read_9862(0,21))    frequency tuning word
'0x0'
>>> hex(sink._read_9862(0,22))
'0x0'
>>> hex(sink._read_9862(0,23))
'0x28'
>>>

0x280000 is 2621440, 0xFFFFFF is 16777215 (creates dds = Fdac/4 ), and
2621440/16777216 * 32e6 = 5e6   qed.

--Chuck