feat(blocks): SignalSource

[loic-fejoz]

Add a new block called SignalSource which is the counter part of the GNURadio block.

In particular, it is based on phase being encoded as fixed float and use the same underlying mechanism. It thus provides sine, cosine, square, and triangle signals on f32, and wave for Complex32. One can also use it with a generic phase to amplitude convertor function.

Moreover, it add an example in order to compare several oscillators implementation. One can retrieve via ZeroMQ the signal in GNURadio to compare the FFT and the stability of the signal.

I also added a min_item to the ZeroMQ PubSink in order to avoid sending too many packets.

NB: I would recommend to remove the Oscillator block in favour of this implementation.

[bastibl]

Wow, you went deep into the rabbit hole :-) I can do some follow-up commits to remove the oscillator, as you suggested. I'm just not sure about the difference between offset and initial_phase. Shouldn't only one be required? Or maybe I'm misunderstanding things.

I'd also change the builder to make sample rate and frequency a required parameter, something like:

SignalSourceBuilder::sin(freq, samp_rate).build();
SignalSourceBuilder::cos(freq, samp_rate).amplitude(2.0).build()

Would this be fine for you?

[loic-fejoz]

Yes indeed the hole was deep ;-)

offset is about the DC component of the resulting signal, while initial_phase is ...well the initial offset in the phase. So indeed, we need both.

            let a = (self.phase_to_amplitude)(self.nco.phase);
            let a = a * self.amplitude;
            let a = a + self.offset;

Otherwise, I am fine with your proposal.

[bastibl]

It's merged with the suggested follow-up changes. Thanks!