[Tinyos-devel] Current status of the message buffer discussion

[Miklos Maroti]

On Mon, May 11, 2009 at 6:34 AM, culler <culler at cs.berkeley.edu> wrote:
> Classically, on the inbound path you have a contiguous packet with the
> telescoping layers of encapsulation.  The trick is the outbound path, since
> each layer does not know what the layers around it want to wrap around it.
>  Classically, you build a list of these (mbufs) as you go down and perform a
> gather as it goes out.  Or, you need to determine from the layers below what
> they need.  All of addresses and header fields aree just encapsulating
> information.  Given that our processors are really fast compared to these
> paltry radios, it is not obvious that gather is a problem.  Very retro, but
> there is a reason that it was done in the old days.

Gather would be very nice and flexible, but probably it would waste memory.

David, could you please shed some light on what is the final goal?
What exactly do people want to archive that requires variable size
headers? It is not enough for me to say that 16 and 64-bit addresses,
because I also want to know what interfaces you want to use. Do people
have two interfaces in mind, one AMPacket to access 16-bit and another
for 64-bit, or we want to have two AMSend interfaces, one with 16-bit
and one for 64-bit, or we want one interfaces to be able access both
16 and 64-bit addresses, or we want to always use 64bit addresses in
software but would like to be able to receive 16-bit addresses too and
cast them to 64-bit?

My real question is: how application developers want to interact with
the message buffer? I would like to see use cases.

Miklos