Re: [Discuss-gnuradio] Packet Header Generator

[Ed Criscuolo]

On 11/14/14 4:49 PM, Tom Rondeau wrote:
> On Fri, Nov 14, 2014 at 3:14 PM, Ed Criscuolo
> <address@hidden <mailto:address@hidden>> wrote:
>
>     I'm trying to use the Packet Header Generator block
>     (not the Default one) from within GRC to generate a
>     packet header formatted to my own specification in
>     order to match an existing protocol.
>
>     I assume that an appropriate "formatter object" can
>     be submitted to this block to instruct it to build an
>     arbitrary header, but I'm having difficulty finding
>     any documentation or example of using a formatter object.
>     All I found points to the packet_header_default::header___formatter
>     method, which composes a fixed format that is of no use to me.
>
>     Any help point me in the right direction?  Am I just missing
>     it or is there no "generic" header formatter capability?
>
>     @(^.^)@  Ed
>
>
>
> Hey Ed,
>
> Funny enough, I was just working on this today. I'm adding a similar
> packet header generator for async (PDU-based) packets. The concept is
> similar with a default base class that you'd overload for your own
> purposes for packet formatting. I'll be documenting this behavior more
> in the blocks themselves, and this should eventually become the basis
> for another level of our tutorials.
>
> I have it working here in simulation, but I know there's going to be
> some trouble going over the air. I suspect I'll have something that's is
> worth sharing and reasonably documented early next week.
>
> Tom


OK.  Meanwhile, is there some clever Python hack I can use in the
interim?  I'm trying to get a timetag in a specific format
(64-bit integer, LSB=250 picoSeconds) into the header I'm generating.
It has to increment by 0x0000000000028000 for each packet.

For example, for my sequence number field, I needed a 16-bit unsigned
number that skipped over any value where the last 5 bits are '1',
and rolled over at 2**16.  I used a repeating short vector source
with the Python list comprehension

[s for s in range(0,32768)+range(-32768,0) if s%32 != 31]

as the vector entry in the GR block.  This got merged with the
other header fields via stream mux block. It worked great.

But for the timetag, I don't have the rollover which allowed
me to pregenerate a a fixed (large) vector.  Any ideas?

@(^.^)@  Ed