Re: [Discuss-gnuradio] how to implement synchronous source block correctly ?

[Marcus Müller]

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> Btw, this restriction frustrating. Someone would like to make
> useful
graph
> containing both audio source and sink in single chain, but it's
impossible
> due to current GNU Radio design.
As I told you before: That's plainly not true.
There are a lot of flowgraphs that have both hardware sources and sinks.
Why your's not working is a mystery to me, because, seriously, audio
sample rates should pose no problem for a moderately capable PC,
unless you do something complicated.

> I think it would be better to implement such scheduler which do 
> synchronization itself (using software generator or some external
> source provided by user).

The scheduler is a *scheduler*, it schedules the calling of the work
functions. I don't think you realize the implications of designing a
per-sample real-time signal processing framework. It basically
eradicates the possibility of having variable computational costs in
each block.
And, by the way, I think you over-estimate the real-time abilities of
modern operating systems on modern PC hardware. If you want to have a
guaranteed "sample clock" in GNU Radio, you would need HUGE amounts of
spare computational power. That'd be a waste.
GNU Radio works on *blocks* of samples. This implies latency, and
makes it impractical to say "ok, that single sample always comes every
x µs", but it gives you the advantage of a buffer, so that you can
have actual hardware interaction with your SDR.

Having a hardware defined sample rate basically does exactly what you
want.
And: If you're looking for an innovative GNU Radio scheduler, look
into GRAS (GNU Radio advanced scheduler), it has a different model of
block interaction, but of course /can't/ take the route of
time-synchronous per-sample processing. That's just anti-SDR, to be
honest.

Greetings,
Marcus
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