Re: [Discuss-gnuradio] Changing Nout_items and Buffer Settings for GNURadio 3.6.2

[Tom Rondeau]

On Wed, Feb 6, 2013 at 1:34 PM, Tom Hendrick <address@hidden> wrote:

Hello,

I think its possible some of the underrun issues I mentioned in my other posts (where random gaps occur inside a block of data sent to the USRP when set the USRP sampling frequency any lower than 1 MHz,) may be solved by tweaking nout_items and buffer related settings.

For GNURadio 3.6.2, Is there a simple way to modify the python code generated by GRC in order to change those settings?  I had seen instructions for doing this with 3.6.3 but I think they don't apply to the 3.6.2 version.  I can consider upgrading to 3.6.3 if there isn't an easy solution.

Thank you, Tom

You can tweak the max noutput_items in 3.6.2. You can pass a value to the top block object when you run start/run that will set the maximum value noutput_items can be.

In 3.6.3, you now have the ability to change the maximum noutput_items on a per block basis with block.set_max_noutput_items (this might be doable in 3.6.2; I forget when we added it). You can also change the buffer sizes of a block before you start the flowgraph with set_max/min_output_buffer.

There should be very little concern going between 3.6.2 and 3.6.3. We maintain API compatibility between those versions.

But, having said all of this, I'm not sure this is really going to help you. Are you thinking of decreasing the buffer sizes or the max noutput_items? That's actually going to hurt you computationally. It will lower latency, but it means less time inside a work function and more overhead in the scheduler, moving things around, and context switching. Larger buffers mean more time in work for each block, which is when you get the most power.

Tom