Re: sample rate with selector and throttle blocks

Richard,

   Thanks for the quick reply. I understand the need for a throttle.
However, in my case, if the selector block selects the path holding the
throttle block then the hardware does not appear to throttle which makes
sense because the hardware isn't being fed data; in this case the CPU
then runs wild.  I am seeking confirmation that reciprocity holds in
that if the throttle block is not receiving a stream of data (not in the
active path), it will then have no impact and the hardware will
determine the actual sample rate.


Rick

On 2025-05-29 11:13, Richard Bell wrote:
> Hello,
>
> TLDR: If you are using hardware in your flowgraph, which I think you
> are, then you should not include a throttle block. Only use throttle
> blocks in flowgraphs with no hardware limitations (i.e. reading from
> files or generating synthetic data on the fly).
>
> The throttle block is intended for software only scenarios, in which
> you want to limit the rate at which your CPU gets called to make
> computations. The throttle block simply invokes a call to sleep to
> artificially "throttle" the CPU usage. It is not related to the
> contextual sample rate of the underlying stream of data. Using a
> throttle block with hardware can cause unintended issues where you
> can't keep up with the rate of the hardware.
>
> For example, I could record data to a file from a radio with a sample
> rate of 1 Msps. If I play back that file and plot it in GNU Radio, I
> could use a throttle with any rate I want to limit CPU usage, but the
> underlying sample rate of that data will always be 1 Msps. The rate of
> CPU usage and the underlying sample rate of data are not coupled.
>
> Richard
>
>
>
> On Thu, May 29, 2025 at 10:57 AM aardric via GNU Radio, the Free &
> Open-Source Toolkit for Software Radio <discuss-gnuradio@gnu.org> wrote:
>
> Hi,
>
>    Could someone please confirm my understanding that the sample
> rate in
> the attached flow graph will be determined by the active path of the
> second (from left) selector block and NOT the throttle block (that
> is,
> if throttle not selected)?  This would be consistent with the block
> documentation for the selector block on the wiki.
>
>
> Rick
>