Taking this to the list.
-------- Forwarded Message --------
Subject: RE: [ARTIQ] Today's slides
Date: Mon, 18 May 2015 20:53:39 +0000
From: Slichter, Daniel H. <[email protected]>
To: Jordens, Robert <[email protected]>, Sébastien Bourdeauducq
<[email protected]>, Britton, Joe <[email protected]>
>> 1. Programmable modulus mode. The appropriate modulus should be
>> calculated by the master in the compilation stage, as it may be
>> computationally expensive to do so on the SoC. For most
>> applications, exact frequency synthesis may not be necessary and
>> simply using programmable modulus simplistically to add effective
>> bits to the FTW (e.g. setting B=2^31 and varying A for fine frequency
>> tuning, see AD9914 data sheet) may be sufficient and simpler to
>> implement.
I think this simplistic mode of operation, which gives additional
effective bits in the FTW but does not try for exact frequency
synthesis, should meet 99% of the needs of typical users. I would
advocate going ahead and implementing this simple B=2^31 solution for
now. We would need to determine how exactly to expose the functionality
to the user. One option would be to have a mode for the DDS, like the
phase mode, which might be called "resolution". So then we would have a
method set_resolution(self, resolution), with two options,
STANDARD_RESOLUTION and FINE_RESOLUTION. The first option would just
use the usual 32-bit FTW (profile mode with profile 0), and the second
would use programmable modulus mode, setting B=2^31 to give you an
effective 63-bit FTW. If you leave profile mode enabled, then the
amplitude and phase settings for the current profile determine amplitude
and phase of the output, while the programmable modulus determines
frequency.
If we are not implementing profile mode or digital ramps right now, this
should be a very straightforward addition to make. I think that most
users in our group are interested in the AD9914 at least in part because
of the option of an increased-resolution FTW, so I think we really
should have at least this basic capability enabled.
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