On Tue, 2006-07-11 at 23:03 -0500, Larry Finger wrote: > Dan Williams wrote: > > > > NAK... remember, range->max_qual.level must be _0_ if you're in dBm, > > I do not think this is right. From the comments in include/linux/wireless.h: > > /* Quality of link & SNR stuff */ > /* Quality range (link, level, noise) > * If the quality is absolute, it will be in the range [0 ; > max_qual], > * if the quality is dBm, it will be in the range [max_qual ; 0]. > * Don't forget that we use 8 bit arithmetics... */
Jean, what's the official word on range->max_qual.level? I don't know where I came up with the requirement that max_qual.level must be 0 to indicate that the units are in dBm (as opposed to RSSI), but it might well have been because we had no way to detect RSSI vs. dBm before IW_QUAL_DBM was added as a flag in WE-19, and therefore using level = 0 was the only reliable way because 0 is the theoretical "max" level that most cards can handle. So if you want to express your quality in dBm, you have a choice; either set IW_QUAL_DBM explicitly and do what you want with max_qual.level, or set your max_qual.level to 0. That's my interpretation, of course I could be wrong. Furthermore, there's no point to setting your max_qual.level to be the lowest level, since that's what your max_qual.noise is!!! max_qual.noise is the noise floor of your card and that effectively _is_ the lowest level at which your card can operate. In the ideal world, which we are now much closer to, we could _require_ that IW_QUAL_DBM was set, otherwise values would be interpreted as RSSI. And we can if the driver's we_source_version is >= 19. I agree, it's all quite confusing for starters. Jean? > My interpretation of this is that if 0 < max_qual < 128, the quantity is > absolute. Conversely, if > -129 < max_qual < 0, the quantity is in dBm. This is in fact what I see, both > from the KDE applets > and the various wireless extension tools. > > > since 0 is the actual maximum, and your level values are negative since > > they are in dBm. > > > > If KDE network applets display the wrong value when max_qual.level == 0, > > then they are wrong and need to be fixed. > > They display correctly; however, choosing 0 rather than -100 expands the > scale to the point that my > noise values of -65 dBm display as rather high values. Despite the 8-bit > arithmetic, I think it > creates a scale from 0 to -255 dBm. My choice of parameters expands the scale > by limiting the lower > value to -100 dBm. Hm, I didn't think that WE's quality specification took scale into account; AFAIK you get 255 values to play with, and each maps either to an RSSI value of your choice, or to an absolute dBm value. There's no scaling involved AFAIK. > > If you actually want RSSI, then you set max_qual.level to the upper > > limit of your RSSI, and the RSSI is assumed to go from 0 -> > > max_qual.level. AFAIK, the patch you had earlier is using dBm, _not_ > > RSSI, so max_qual.level = 0 is correct. > > As I explained earlier, the RSSI value returned by the firmware has been > processed by the driver > into a quantity that varies between -10 and -65 as the receiver is moved from > very close to very far > from the AP, which looks like strength in dBm. This is what is stored in > stats.rssi. As this seems > to be confusing, I will rewrite the driver code so that this value is > returned in stats.signal with > the RSSI value preserved in stats.rssi. The quality output will be derived > from stats.rssi, and the > level output will come from stats.signal. These two quantities have a > correlation of -1 so there is > no new information, but that might change in the future. So; if you want to use dBm you should probably set IW_QUAL_DBM flag on the qual->updated field when you update level & noise. Then, nothing is ambiguous and everyone knows exactly what you mean. Which is why IW_QUAL_DBM was added, because I complained that quality was too ambiguous. Jean? Cheers, Dan > Larry - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
