Re: [Discuss-gnuradio] Gnuradio clock coherence?

On 11/14/2017 02:13 PM, John Ackermann N8UR wrote:
> What is the clock source for a Gnuradio "internal" source such as the
> Signal Source block? If there is no hardware device connected, is the
> block ultimately driven by the PC clock?
>
> Then, if there is a hardware source (SDR) as well as an internal
> source, does the hardware source provide the master clock for the
> flowgraph, such that any other software-derived sources are coherent
> with it? Or does a Signal Source block still get its clock from the PC?
>
> My real question is whether it's safe to assume that a flowgraph is
> entirely clocked by the samples from its hardware source, and
> consequently that processing within the flowgraph (e.g., oscillator
> and mixer for tuning) does not introduce potential frequency errors.
>
> Thanks,
> John
>
A flow is clocked by the hardware--either by samples being produced or
consumed by the hardware.

The exception is when you use a "throttle" block in the absence of any
hardware. In that case, the PC clock (very roughly) controls sample rate.

So, in the absence of overruns or underruns, the signal processing in a
flow-graph cannot introduce timing errors, unless deliberate a programmmed.




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