Date: Wed, 22 Aug 2012 11:25:08 -0700 From: Adrian Chadd <adrian@freebsd.org> To: "Wright, Brett" <Brett.Wright@cooperindustries.com> Cc: freebsd-wireless@freebsd.org, Kim Culhan <w8hdkim@gmail.com> Subject: Re: Atheros DFS radar detection Message-ID: <CAJ-VmomJZD_NBM8=N1oD1a0XCFLoXoezStXHKLKCSGLBFrKT2Q@mail.gmail.com> In-Reply-To: <475A4E02EFF4724A9E58F55A56AC13160661E6AC@APEVS1.ap.ci.root> References: <CAKZxVQU-%2BW9AP4a9W0PGyLmBOa1GVOrGcLC8bp5zW_=K%2Bv3tHA@mail.gmail.com> <475A4E02EFF4724A9E58F55A56AC13160641D618@APEVS1.ap.ci.root> <CAKZxVQWeOnw_kZWzuXfHSS-ssQfGVG=ybYK%2B%2B8EaqnFVe-rLpg@mail.gmail.com> <CAJ-Vmon=NfyZW9vJRSNxTLZvJhobeCP-S1O3TxopNzArWunCCQ@mail.gmail.com> <475A4E02EFF4724A9E58F55A56AC13160661E6AC@APEVS1.ap.ci.root>
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Hm, let me have a (re)-read of what we have here..
Your false detects - are they long? short? Do they have 0 or no
duration? That'll at least hint at what's going on (ie, triggering on
out of band or in-band stuff; whether it's triggering on 802.11 frames
or not.)
firpwr is the threshold for power estimation. The power estimation
occurs _after_ the AGC (ie, it's the size of the signal _after_ the
AGC has had a few tries at it.)
rrssi is the threshold for long (ie, can do AGC changes) detection.
The RSSI has to be above this for radar "signal" to be considered
occuring. Decreasing it will increase false detects but allow longer,
weaker radar pulses.
prssi is the threshold for short (ie, can't do AGC changes) detection
("pulse"). Once there's an AGC change, the RSSI needs to be below this
value for the event to be considered a pulse instead of a long radar
event.
The Atheros NICs use relative signal levels rather than absolute
levels. It's all relative to what the noise floor is. So as long as
the hardware sees a good noise floor (ie, there's no spurs, 100%
congestion, etc) the RSSI will be relative to something sane (eg ~
95dBm) and you can _almost_ treat it as an absolute level. But, you
really shouldn't. It also means if the NF value is higher for some
reason, the RSSI values will change and the parameters will also
change.
The whole point of tuning the PRSSI/RSSI/Firpwr is to try and make the
hardware detect radar pulses at -62dBm at the device input. This
depends upon the input antenna and any amplifiers. This is why it's
tricky as hell to get right. :-)
I'm going to throw an AR5212 into my laptop now and see what errors I get.
Adrian
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