Re: [Discuss-gnuradio] Question Regarding GMSK2 examples

[Michael Dickens]

On Monday, May 1, 2006, at 08:21 PM, Elaine Garbarine wrote:
> As a related question, does rx_callback only exist if the packet is 
> received
> properly (i.e. without errors)?

In essence, yes: the rx_callback will only be called when a packet is 
received without (*) errors.  See 
.../gnuradio-core/src/lib/general/gr_packet_sink.cc and it's work() 
method and finite-state-machine-ish code if you really want the 
in-depth story.

(*) This happens when enough of the sync bits are correct (either the 
user-supplied value or the default of 12 bits wrong out of 64) and the 
immediately-following 32-bit header is correct (meaning that the first 
16 bits and second 16 bits are identical [correct or not], and that the 
payload length [the integer value of either of the first or second 16 
bits] is <= 4096).  Note that the "function" 'slice()' could more 
reasonably be called "hard_decode_bit()" since that's what it does.

ps> As a general question regarding the gr_packet_sink, why does this 
have to do it's output via a gr_message inserted into a queue?  Why not 
stream the output to the next block in the flow graph style?  Is this 
one of the "message versus stream" issues that BBN's proposal will 
address?  Or is it something to do with carrier recovery and such?  Or 
was the carrier issue why the gmsk2_mod_pkt required queued packets and 
not a stream?