[Tinyos-devel] message_t: starting to tease AM away from Serial and Radio

[Eric Decker]

I'm starting coding to tease the AM code away from the Serial and Radio
stacks to make AM encapsulation more independent from the h/w encapsulation.
The intent is to support the AM encapsulation while moving in the direction
of Jan's and Miklos' suggestions.  I need something like this because I'm
doing dynamic switching of queued packets.  Also I want to understand better
the impact on packetAck and other pinch points with respect to what we are
discussing with regards to encapsulations and the packet buffers.

I'm using the following principals/goals:

1) Packet formats don't change.  The resultant code will be completely
compatible with existing motes with respect to the wire/transmission.
2) Additional control cells are added to the message structure, (encap,
encap_offset (where the current encapsulation starts), length, etc.)
3) One principal is given a packet one should be able to unwrap the packet
just by looking at data in the current header.
4) Header information still resides in the header section of the message
buffer.
5) Application data resides in the current data area.  encap_offset points
at what should currently be considered data for the component that is
currently working on the packet.  When the packet gets to the application
layer, encap_offset will point at the data for the application.
6) All packet data is maintained contiguously, there is no wrap around.  1st
structures have to be contiguous.  Splitting data fields including
application data is problematic and needs to be avoided.

One thing I'm added first off is a newPacket module that is used to access
the packet/message control cells.  It will provide all the usual Packet
interfaces, any new ones will be added to a new interface spec called oddly
enough newPacket.

This is a prototype to explore some of what we are talking about and to gain
better understanding of how changes propagate.

I could use some folks looking over my shoulder and commenting on code,
better ways to do things, etc.  Especially on better ways to do things,
where to put things, naming etc.

Thoughts,

eric

-- 
Eric B. Decker
Senior (over 50 :-) Researcher
Autonomous Systems Lab
Jack Baskin School of Engineering
UCSC
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