[net2-wg] header format changes (?)

[Stephen Dawson-Haggerty]

Sure. The change was adding support for simple Ieee802.15.4 messages to the
cc2420 radio stack; the description of how to do this I sent out a few days
ago is below, which I think covers it.  I'd be happy to clarify anything
that is unclear but the actual change is pretty straightforward,  I
believe.  I can send a patch if that would help people get a feel for what
I'm proposing.

Currently, the cc2420 header sits inside the header region of a message_t,
and the application payload starts with the first byte of the data region.

We will not change this for active messages.  However, we will consider
packets where the "network" byte of an I-frame is not
TINYOS_6LOWPAN_NETWORK_ID to be 802.15.4 packets.  Therefore, the payload
region of these packets will start with the network byte of the header.
Note that this will NOT be aligned with the data region of the message_t; it
will start two bytes earlier.

This is an issue for bridging these packets to serial, but as long as the
person doing the forwarding is aware of it, it's not a big deal.  I have a
patch that makes these change and both AM and non-AM modes work fine.  This
approach has the virtue of it being the one that seems least likely to break
existing code.

Here's what the interfaces would do.

>     interface Receive as IEEE154Receive;


Receive packets where the cc2420header->network is not
TINYOS_6LOWPAN_NETWORK_ID.  The "Payload: would point to
&(cc2420header->network) and then length will include the network and type
bytes.

>
>     interface IEEE154Send;


Send a 15.4 packet.  Basically the same as regular send but don't reference
active message ids.  The length value passed in does not include the network
and type fields of the cc2420 header.

>
>     interface IEEE154Packet;


More or less an AMPacket interface with the type-related commands removed.


>
>     interface Packet as SubAMPacket;


A Packet, which considers the payload to start at the network byte, not
after the am type byte.


On Wed, Feb 11, 2009 at 4:20 PM, Philip Levis <pal at cs.stanford.edu> wrote:

>
> On Feb 11, 2009, at 11:55 PM, Stephen Dawson-Haggerty wrote:
>
>  I'm going to go ahead and assume that the lack of discussion means people
>> are okay with this change since it shouldn't break anything.  Anybody
>> disagree?
>>
>
> Can you articulate the change?
>
> Phil
>
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