On Thu, March 6, 2014 10:24 pm, Martin Townsend wrote:
> I was going to start implementing some low level features of the
> 802.15.4 MAC layer in SW such as Inter Frame Gap, Clear Channel
> Assessment (including the backoff algorithm), and Acknowledgements and
> use this to hopefully lay down a basic scheduler for higher level
> features for a beacon enabled PAN.  I'm hoping to get away with just
> using the HR timers and maybe Linux RT if required.

Does your chip actually not implement any of that? I haven't yet seen a
chip that supports 802.15.4 and that cannot at least perform automatic
acknowldgement and CCA/multiple access schemes.

What do you mean with "scheduler for higher level features"?

> Is anyone else already working on this? if not would anyone else find it
> useful?  Also I would appreciate it if someone could explain what the
> slaves list found in the mac802154 private data structure is for?

The slave list contains wpan device instances. struct mac802154_priv
itself does not represent any device, it pretty much only holds on to a
PHY and a list of netdevs that are running on that PHY. I consider this
list a huge mistake, a break of semantics and a hindrance for development;
I'm drafting a proposal to remove this list and a more general
simplification of the stack.

Takeaway: struct mac802154_sub_if_data is where you want to put netdev
specific things, but some stuff is probably best handled by the PHY
driver. I've recently added infrastructure to enabled MAC features of a
PHY chip, like CCA, automatic acknowledgement and retransmit and a few
other things. Even if your PHY does not support any such feature, I think
it is more sensible to do CCA/CSMA in the driver. ACK transmission also
must not happen in the main stack at the moment, because received packet
processing is done in a workqueue and thus involves scheduler.


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