Re: [Discuss-gnuradio] what is the update rate of signal probe/probe function ?

[Marcus D. Leech]

On 03/10/2016 10:53 AM, apchar wrote:

Try this simple flow graph. A waveform generator feeding a scope & a signal probe that's feeding a probe function that's driving a constant generator thats feeding a scope. Set the update rate of the probe function to the system sample rate. You'll see on the scopes that the update rate of the probe output is no where near the original. Why ? What is the actual update rate of the signal probe/probe function combo ?

If you want to process signals at the sample rate, you need to use existing blocks, or write one.

The probe infrastructure is designed for occasional probing of the sample stream, not as a replacement for writing an actual sample-processing
  block.

A "probe" block has a probe function, typically, called "level" which returns the current sample value at the time the probe is called.
  A "function probe" block is a way of creating a thread within the generated python that simple polls this function at whatever
  (reasonable) rate you request.  If you look at the generated code for function probe, it's just a while loop, with a "sleep" at the bottom of
  it corresponding to your desired rate.  Asking for a rate beyond a few 10s per second is not going to work very well, both because this is
  Python, and because achievable wake-up rates even on a modern CPU with a modern kernel like linux aren't going to be anywhere close
  to the kinds of rates required to process at typical input sample rates.