CVS-2-2 ipw2200 NMApplet bar empty patch

The function nm_wireless_qual_to_percent has a pointer to the max_qual structure as its second argument. In the ipw2200 driver

max_qual->qual = 100;
max_qual->level = 0;

I changed this to

max_qual->qual = 100;
max_qual->level = PERFECT_RSSI + 0x100;
max_qual->noise = WORST_RSSI + 0x100;

The second two values are biased dBm values. Each driver has its own way to compute percentage from RSSI values. Formulas vary based on the units RSSI is measure in. In some cases a lookup table is used. To get a rough indicator of percentage signal level for use in the NMApplet bar, I modified the nm_wireless_qual_to_percent function as indicated below. Now the NMApplet hover gives percentage values consistent with what I get from iwconfig for the associated AP and the NMApplet bars show for each scanned AP an approximate signal level. My percentage signal level formula is a linear model which underestimates the signal level say in comparison to the values that Windows XP reports. If a driver does not set max_qual->level and max_qual->noise, the nm_wireless_qual_to_percent function could make some guesses.

RSSI in dBm is measuring a real physical quantity power. Percentage signal level is a man made device. I wonder what value it really has. If you are doing a building site map say for 80211B, what you really want to do is to find the 11Mbps areas, the 5.5Mpbs areas, the 2Mbps areas, and the 1 Mbps areas. This type of information gives the user an indication of throughput which is more useful than a percent. What the heck does 80% mean in the wireless world across drivers -- next to nothing.

/* Try using the card's idea of the signal quality first as long as it tells us what the max quality is */ if ((qual->qual != 0) && (max_qual->qual != 0) && !(max_qual->updated & IW_QUAL_QUAL_INVALID) && !(qual->up
percent = (int)(100 * ((double)qual->qual / (double)max_qual->qual));
if ((qual->level !=0) && (max_qual->level !=0) && (max_qual->noise !=0))
                       percent = (int)(100 - 70*(
((double)max_qual->level - (double)qual->level) / ((double)max_qual->level - (double)max_qual->noise)));
else if ((qual->level > max_qual->level) && (qual->noise != 0))

Bill Moss
Professor, Mathematical Sciences
Clemson University

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