> ath5k dBm dBm percent rssi
> b43legacy dBm(?) dBm percent jssi(?)
> b43 dBm(?) dBm percent jssi(?)
> iwl-3945 dBm dBm percent snr+more
> iwl-4965 dBm dBm percent snr+more
> rt2x00 dBm(?) n/a percent rssi+tx/rx frame
> success rt2400 dBm(?) n/a
> rt2500pci dBm(?) n/a
> rt2500usb dBm(?) n/a
> rt61pci dBm(?) n/a
> rt73usb dBm(?) n/a
> rtl8180 nounit n/a (?)
> rtl8187 nounit (?) (?)
> zd1211 dB(?) / percent
This list made me think about the libertas values. Here the
firmware provides SNR and NF and RSSI is calculated from those
values. However,
Is it ok to add a dBm value (noisefloor) to a dB value (SNR) ??
The libertas firmware can give me SNR and NF for beacons (via
CMD_802_11_RSSI) and also for each received frame (in the rx
packet descriptor structure).
In the firmware manual they say:
SNR UINT8 Signal to noise ratio for this packet
This should be a positive value (dB)
NF UINT8 Noise floor for this packet (dBm)
Noise floor is always negative. The absolute
value is passed.
That was the description for the RX packet descriptor, the
description for the CMD_802_11_RSSI is basically the same.
Now I see two macros:
#define CAL_NF(NF) ((s32)(-(s32)(NF)))
#define CAL_RSSI(SNR,NF) ((s32)((s32)(SNR) + CAL_NF(NF)))
While I understand the CAL_NF() macro, but I'm not sure if the
second one does the right thing. Or maybe the manual is simply
wrong. Here are some samples with my WLAN card sitting next to
an AP:
rxpd: SNR 41, NF 86
get_rssi: SNR 41, NF 86
rxpd: SNR 41, NF 86
get_rssi: SNR 42, NF 86
rxpd: SNR 41, NF 86
get_rssi: SNR 41, NF 86
rxpd: SNR 41, NF 86
get_rssi: SNR 41, NF 86
get_rssi: SNR 40, NF 85
rxpd: SNR 41, NF 86
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