Re: [Discuss-gnuradio] bbn_80211b_rx.py: how is the received packet handled please?

[masond]

Inlined responses:

Quoting yyzhuang <address@hidden>:
> Hello,

Hi,

> In the BBN 802.11 package, I see the scripts for receiver, and some lines of
> code for packet handling as well.
>
> ======================================================
> def rx_callback(ok, payload):
>     size = struct.calcsize("@qHBB");
>     packet_data = payload[size:];
>     hdr = struct.unpack("@qHbB", payload[0:size]);
>     if len(packet_data) > 16:
>         data_hdr = struct.unpack("@BBBBBB", packet_data[10:16])


> What does the struct.unpack do? Is it for formatting the packet for display?

Pretty much -- though it does more than that as well.
http://docs.python.org/lib/module-struct.html
struct.unpack() is also used by the mainline gnuradio code (see  
gnuradio-examples/python/(digital|ofdm)/benchmark_* for instance).

> coz when I tried to do this:  print "payload: %s" % payload, what got
> displayed on the screen is like this:
> payload: <binary garbage snipped>

That's because the 'payload' string isn't ascii- or unicode-formatted;  
it's raw binary data packed into a string because that's how python  
handles things that would be stored in a c struct.
If you unpack it with an appropriate format string, you can display  
the actual data received. (something close to but less ugly than
    struct.unpack('!' + `len(payload)` + 'B',payload)
depending on what you want to see.)


> And what exactly the "time" is? As I see in the script, is it in ticks?
> means the time instance, or the inter-arrival time?

I'll defer to someone who's familiar with the BBN code.

--Mason