[Discuss-gnuradio] Dynamically updating vector sources

[Davide Zanetti]

Hello!

I have a question regarding vector_source_c:

After the 
src = gr.vector_source_c (xxx, 1) where xxx is a list of samples
self.connect (src, dst)  where dst is the ursp
and having started the flow (fg.start())

is it possible to change/append/add values to the complex vector ("src" 
in the previous lines) in a way of dynamically changing what it is sent 
to the usrp?

For the big picture, this what I am trying to do:
I want to build a simple UHF rfid reader, partially implementing the EPC 
G2C1 standard.  Basically, only the part used to read the ID from a 
single tag (no writing on the tag, no multiple tags).
The encoding is PIE and the modulation PR-ASK. The commands needed to 
read a single tag are just 4, having between 8 and ~44 bits each.

My initial idea was to build vectors containing the baseband signal for 
each of the 4 commands, and then use those vectors as source for the 
uspr.sink.

I actually did this: I created two lists that represent the bit 0 and 
bit 1 (each one containing the samples that represent bit 0, resp. bit 
1, as PIE-encoded and PR-ASK-modulated with sampling rate at 1MS/s), and 
put together those lists to compose the individual commands (which are 
simply a sequence of bits).
Then, I properly concatenated those commands ("properly" = respecting 
the order and timing of the standard), created the vector source, and 
linked to the usrp sink (as shown above).
The sequence is correctly transmitted (so, the baseband signal contained 
in the vector source is up-mixed and sent out by the usrp) and the tag 
is actually responding back.

Now, I would like to decide which command to send (and set its fields) 
and a step-by-step mode. That is, set and send command A, then do 
something (e.g., receiving a tag response), set and send B (e.g., 
setting it according to the previous tag response), and so on, instead 
of composing the entire communication at once with possibility of 
interacting.

Thanks!!

Davide