Making a Gnuradio Settings block

Question

We're going to be using Gnuradio to stream in data from a radio peripheral. In addition, we have another peripheral that is part of the system which control programatically. I have a basic C program to do the controls.

I'd like to be able to implement this in GNUradio, but I dont' know what the best way to do this is. I've seen that you can make blocks, so I was thinking I could make a sink block, have a constant feed into that, and have the constant's value defined by some control like a WX slider.

It would take a needless part out of this if I could remove the constant block and just have the variable assigned to the WX slider directly be assigned to the control block, but then there would be no input. Can you make an inputless and outputless block that just runs some program or subroutine?

Also, when doing a basic test to see if this was feasible, I used a slider to a constant source to a WX scope plot. There seems to be a lag or delay between putting in an option and seeing the result show up on the plot. Is there a more efficient way to do this that will reduce that lag? Or is the lag just becasue my computer is slow?

Answer 1

I would guess you need a throttle in your work flow diagram or the sampling rate between blocks is incorrect.

It's almost impossible to help you unless you post your grc file or an image of the it.

Answer 2

It would take a needless part out of this if I could remove the constant block and just have the variable assigned to the WX slider directly be assigned to the control block, but then there would be no input. Can you make an inputless and outputless block that just runs some program or subroutine?

Yes, if you do this it will work. In fact, you can write any sort of Python code in a GRC XML file, and if you set up the properties and setter code properly, what you want will work. It doesn't have to actually create any GNU Radio blocks per se.

Also, when doing a basic test to see if this was feasible, I used a slider to a constant source to a WX scope plot. There seems to be a lag or delay between putting in an option and seeing the result show up on the plot.

GNU Radio is not optimized for minimum latency, but for efficient bulk processing. You're seeing the buffering between the source and the sink. Whenever you have a source that computes values rather than being tied to some hardware clock, the buffers downstream of it will be always-nearly-full and you'll get this lag.

In the advanced options there are settings to tune the buffer size, but they will only help so much.