[Discuss-gnuradio] Problems writing an OOT block

Dear All,

 I want to write ablock where:

The output is the the Inverse of the input,

The output is "1" if there is no input.(It acts like a source)

I am confused how to implement the part where the Block behaves like a Source.

In one mode you need an Input to produce an output (ninput_items_required=1)

and in one mode you need no Input to produce an output (ninput_items_required=0) .

I have looked at the forecast() function where the "relationship between noutput_items and the requirements for each input stream" is defined.

Also I could not figure out how the next block requests samples from the curent block.

Can anybody help?