[riot-devel] at86rf2xx and PHR filtering

Alexander Aring alex.aring at gmail.com
Fri Apr 1 10:57:37 CEST 2016


On Fri, Apr 01, 2016 at 08:45:48AM +0000, Wachtler, Axel wrote:
> > Most datasheets doesn't say anything what they filter on PHR or not.
> 
> 
> 
> The MSB in the PHR field is reserved, see at86rf230 DS:
> 
> 
> 
> [cid:image001.png at 01D18C02.AB62FEF0]
> 
> 
> 
> At and after RF231 this Bit could be sent by the transceiver and can then be seen at the receiver site as well.
> 
> 
> 
> Also the standard tells that this bit is reserved, so proper implementations needs to mask this out in order
> 
> to get the correct frame length at the receiving site.
> 

Okay, then all transceivers need to do that and mostly at driver layer
because at the tail are mostly LQI/RSSI information.

But it's not just the MSB bit, there are also some other "len" values
which are reserved:

256  *      0-4     Reserved
257  *      5       MPDU (Acknowledgment)
258  *      6-8     Reserved
259  *      9-127   MPDU


If you received one which is reserved then you know:

"It's an invalid 802.15.4 frame".

Question is how to react on that, already drop then on driver layer ->
because it's part of phy layer and not mac layer. Or simple do what we
do with deliver the full 127 byte frame to mac layer.

We assume then something weird happend on the air. :-)

- Alex


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