802.11 RSSI value displayed from ifconfig(8)

[Sam Leffler]

Eduardo Meyer wrote:
> Hello, I would like to convert RSSI to dBm (in fact I would love if
> ifconfig cound display SNR in dBM), so I would like to know if this
> formula is any right:
> 
> /* Calculate the RSSI Value */
> V_RSSI = 3.0 * (RSSI_VAL/1024);
> RSSI_dBM = (int8_t) ((-50.0 * V_RSSI) - 45.5);
> 
> And if there are any other tools which can help me finding out signal
> stenght, when I am acting as an access point.

ifconfig reports rssi as whatever the driver provided.  The intent is
that it be a signed value relative to the current noise floor (both in
dBm).  If you look at the output of wlanstats
(tools/tools/net80211/wlanstats) or, for ath devices, athstats
(tools/tools/ath/athstats) you will see the default displays show
"signal" which is rssi+noise-floor in dBm.  The main issue(s) right now
are that the net80211-driver api does not pass noise floor up so it can
be reported to user apps and drivers reports rssi+nf in varying units.
athstats doesn't have that issue since it queries the driver directly
(hence it's display has a reasonable noise floor).

It's on my todo list to push signal-related data up properly and fix
ifconfig so it displays a proper signal strength in the normal status
display.  The issue of units is more difficult as converting data for
some devices to dBm can be tricky.

	Sam