Execute python code when tag detected

[Lukas Haase]

Hi,

Is there a standard way/block in GRC to execute python code when a block 
receives a certain tag, if possible (without writing a complete block from 
scratch)?

Two days ago I have asked about the best way to implement frequency hopping. In 
absence of advice I am unfortunately still heavily struggling with this. I have 
played around a lot with "Probe Signal" and "Probe Function" but this doesn't 
seem to be reliable at all (and I found Marcus Mueller saying that this 
approach would be the wrong one most of the time).

Now I am playing with tags. My idea is to generate tags at the hop rate using 
"Tags Strobe":

https://paste.pics/413ea9ea71991af42c0c86bc91ccb34b

I am looking for a way to execute the following code when such a tag is 
received downstream:

1.) Update the "Value (PMT)" to reflect the next hopping frequency. I think of 
having my hop pattern as vector, the tag value  
pmt.from_float(frequencies[idx]) and whenever the tag is detected downstream, 
execute "idx = mod(idx+1,frequencies.length())"

2.) Create a tune request and update USRP Source/Sink to reflect new center 
frequency. I am aware that it is possible to use messages to change center 
frequencies of USRP objects. However, I need TX/RX to be fully coherent, so I 
need to use timed commands and integer mode PLL in order to.



Furthermore: Is there a standard way to "convert" a tag to a message? I.e., 
create a message event whenever a certain tag is detected in the stream?


Thanks,
Luke