[Tinyos Core WG] TKN15.4

[Miklos Maroti]

Dear Jan,

How much glue code is necessary? I would like to take a look if the
RF230 could be supported, and actually try to do it. That would be the
real test whether it is platform independent. Where can I take a look?
Is the "glue" documented?

Miklos

On Wed, May 21, 2008 at 4:56 PM, Jan Hauer <jan.hauer at gmail.com> wrote:
> As discussed in the last conference call, here is an update on our
> 802.15.4 implementation, on how the code is structured and how it
> could be integrated into the T2 core.
>
> The main part is a platform-independent 802.15.4-2006 MAC
> implementation, structured into a set of about 20 components (a total
> of 5k lines of code), providing the standard 15.4 interfaces slightly
> adapted to the T2 design philosophy (e.g. using message_t and buffer
> swapping). The implementation currently includes the beacon-enabled
> mode (I'm working on the non-beacon-enabled mode) and almost all of
> the functionality described in the standard, except GTS and security.
> I have developed it on telosb and plan to port it to tossim soon.
>
> The MAC has some requirements (uses a set of interfaces) that I found
> "problematic" to implement with the current T2 codebase, at least on
> the telosb platform which I used for development: it requires
> Alarm/Timer interfaces with a precision of a 15.4 symbol (62.500Hz in
> the 2.4 GHz band) and it requires radio interfaces that allow to
> precisely control when a packet is transmitted. These requirements are
> caused by the fact that the 15.4 standard expresses backoffs in symbol
> times and in the slotted CSMA-CA (beacon-enabled mode) packets must be
> sent exactly on backoff boundaries defined through the previous
> beacon. For telosb we have developed a small 62.5Khz timer-board that
> can be attached to the telosb expansion header, but I have not yet
> checked whether other T2 platforms might be able to generate 62.5Khz
> Alarms (+-40ppm accuracy) without additional hardware. As for the
> radio interfaces: basically these are async interfaces for Tx/Rx/Off,
> where the Tx interface allows to specify the absolute time (t0+dt)
> when the packet is to be transmitted.
>
> Ideally a radio driver providing these Tx/Rx/Off interfaces to the
> 15.4 MAC should just be a wrapper that sits on top of an existing T2
> radio stack. For the CC2420, however, I had to slightly modify the
> current CC2420 radio stack/interfaces to achieve the necessary timing
> - maybe a future radio TEP could define interfaces (or guidelines) for
> structuring radio stacks, so that implementation of
> platform-independent MACs can be made easier and we can avoid code
> duplication.
>
> Finally, in order to use the MAC there needs to be some
> platform-specific glue code (a configuration) to wire the MAC
> implementation to the particular radio driver and to the Alarm/Timer
> interfaces (and also to define some constants like guard times, etc.).
>
> I have successfully done some basic interoperability tests of our 15.4
> implementation (we call it "TKN15.4") running on a telosb with TIMAC
> running on a CC2430DB (TIMAC is a commercial 15.4 implementation by
> Texas Instruments). It will probably take me another 2 weeks to finish
> the implementation/tossim port and perform some more evaluation;
> meanwhile I plan to write a TEP on TKN15.4.
>
> However, I think we have not yet established rules on how a
> platform-independent MAC would be put into T2 core. I would suggest
> the following:
>
> + the platform-independet MAC implementation/interfaces go into
> tos/lib/mac/tkn154/
> + the platform-specific glue code goes into tos/platforms/<platform>/tkn154/
> + test apps go into apps/tests/tkn154
> + I'm not sure, however, where the modified CC2420 radio driver would go...
>
> Jan
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