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ieee80211_input(9)

The  layer  that supports 802.11 device drivers requires that re‐
ceive processing be single-threaded.  Typically this is done  us‐
ing  a  dedicated  driver  thread.   and  process received 802.11
frames and are designed for use in that context; e.g.  no  driver
locks  may  be  held.   The  frame passed up in the must have the
802.11 protocol header at the front; all device-specific informa‐
tion and/or PLCP must be removed.  Any CRC must be stripped  from
the  end  of  the  frame.   The  802.11 protocol header should be
32-bit aligned for optimal  performance  but  receive  processing
does  not  require  it.  If the frame holds a payload and that is
not aligned to a 32-bit boundary then the  payload  will  be  re-
aligned  so  that it is suitable for processing by protocols such
as If a device (such as inserts padding after the  802.11  header
to  align the payload to a 32-bit boundary the capability must be
set.  Otherwise header and payload are assumed contiguous in  the
mbuf chain.  If a received frame must pass through the A-MPDU re‐
ceive  reorder buffer then the mbuf must be marked with the flag.
Note that for the moment this is required of all frames  received
from  a  station  and TID where a Block ACK stream is active, not
just A-MPDU aggregates.  It is sufficient to check for in the  of
the  station's  node  table entry, any frames that do not require
reorder processing will be dispatched with only minimal overhead.
The parameter is the Receive Signal Strength  Indication  of  the
frame  measured in 0.5dBm units relative to the noise floor.  The
parameter is the best approximation of the  noise  floor  in  dBm
units  at  the  time  the frame was received.  RSSI and noise are
used by the layer to make scanning and roaming decisions in  sta‐
tion mode and to do auto channel selection for hostap and similar
modes.   Otherwise the values are made available to user applica‐
tions (with the rssi presented as a  filtered  average  over  the
last ten values and the noise floor the last reported value).



































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