Re: [Madwifi-devel] disabling the carrier sensing

[Eric W A. <Eric.Anderson@Colorado.EDU>]

Here's a patch to disable CCA, doing pretty much that:

https://systems.cs.colorado.edu/projects/carp/wiki/WikiStart

I've verified that it works on x86 and XScale architectures with at least two
5212 and 5213-based cards.  "Verified" is a tricky word, of course.  All I can
say is that it's passed everything I've been able to throw at it.  I used a
signal analyzer to verify that it's actually tramsmitting, and a signal
generator provide input which should trigger a back-off.  At the very least,
the patched driver will Tx over:
  * A sine wave
  * Continuously modulated FM
  * Continuous 802.11g-like OFDM
  * A continous stream of 802.11g packets (meaning no pause between frames)
  * A stream of 802.11g packets with a 100 usec pause between them.

I've tried these at a range of power levels, and it seems to work at all
levels.  At the very least, it works up to a level where the "background"
signal completely drowns out the wifi card and it becomes impossible to tell.
At that point, the *received* power of the background signal exceeds the
*transmitted* power of the card by > 10 dB, which should basically never happen
in the wild.

-Eric

Thus spake Lrj (ren...@gm...):

>    Hi, Cool Fire
>          I've tried to disable the CCA some time earlier, but I don't verify
>    whether it works, and you can try it.
>          The way is to set the noise floor high enough to skip the CCA:
>          First, in the function ath_attach(), add the code "OS_REG_WRITE(ah,
>    0x9864, NOISE_FLOOR);", I set the value of the NOISE_FLOOR to 0x10000.
>          Then, in the function ath_calibrate(), replace most part of the
>    function:
> 
>        #if 1   /* stop the period calibration of noise floor & force a high
>        enough value to the noise floor */
>                OS_REG_WRITE(ah, 0x9864, 0xFFFFFFFF);
>                isIQdone = AH_TRUE;
>        #else
>         struct ieee80211com *ic = &sc->sc_ic;
>         ...................
>        #endif
> 
>         if (isIQdone == AH_TRUE)
>          ath_calinterval = ATH_LONG_CALINTERVAL;
>         else
>          ath_calinterval = ATH_SHORT_CALINTERVAL;
> 
>           Done.
>           And if you verified whether it works, please let me know, I'll be
>    very appreciated.
>     
> 
>      Date: Sat, 12 Apr 2008 23:23:49 -0400
>      From: "cool fire" <coo...@gm...>
>      Subject: [Madwifi-devel] disabling the carrier sensing
>      To: mad...@li...
>      Message-ID:
>             <394...@ma...>
>      Content-Type: text/plain; charset="iso-8859-1"
> 
>      Hello all,
> 
>      For the requirement of my project I need to disable the carrier sensing
>      and
>      transit my packet like Aloha i.e. Tx it when it comes to us. I tried to
>      play
>      around with the AR5K_PHY_NF register but nothing seems to be happening.
>      I
>      have a channel monitor and able to distinguish the packet in terms of it
>      energy. May be there is an issue with NAV/ Virtual Carrier Sensing or
>      something like this I guess. Can someone direct me in the right
>      direction
>      please.
> 
>      I use 5212 card.
> 
>      Thank you.
>      Cool Fire
> 
>    --
>    Best wishes,
>    Lrj, NCI

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-- 
Eric W. Anderson                                   University of Colorado
eri...@co...                      Dept. of Computer Science
phone: +1-720-984-8864                   Systems Research Lab - ECCR 1B54

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