Gr-trellis convolutional coder FSM

Hi,

I’m working on a modulator using a punctured (non-recursive)
convolutional
coder based on a 1/2 rate mother code with length 7.

However I find the documentation of gr-trellis pretty hard to read, I
don’t
really understand how punctuation should actually be implemented.

Are there any additional documents or papers on designing the FSM of a
convolutional coder?

Thanks,
Clemens