Re: CVS-2-2 NMApplet empty bar explained

[Jean Tourrilhes <jt hpl hp com>]

On Fri, Feb 04, 2005 at 04:32:28PM -0500, Dan Williams wrote:
> On Fri, 2005-02-04 at 09:23 -0800, Jean Tourrilhes wrote:
> > 	MAX_RSSI converted to dBm is some totally uninteresting
> > value. It's going to be close to 0 dBm, and a value that has nothing
> > much to do with real operation but just an arbitrary limit on the A->D
> > converter used for RSSI sampling. On the other hand, MIN_RSSI is very
> > relevant, so that's why we use that.
> 
> Jean,
> 
> Right now, WEXT says that (from the comments in iwlib.c) drivers should
> use a max_qual->level = 0 to specify that the value is in dBm, and
> max_qual->level > 0 for RSSI, right?  (ie Absolute and Relative as said
> in iwlib.c/wireless.h)  In other words, the value in max_qual->level
> specifies whether the value in qual->level and qual->noise are signed or
> unsigned, right?  That seems a bit ambiguous to me, easy for driver
> writers to get wrong.

	Yes, you are right, most of them actually get it wrong. In
theory, for drivers using dBm, max_qual->level should be the minimum
RSSI, the noise floor, but that's even harder to comprehend, so I've
accepted them using 0.

> (note that qual->qual & max_qual->qual aren't part of this discussion
> since they should always be a percentage value that people can go 100 *
> (qual->qual / max_qual->qual) with)
> 
> The problem right now is that drivers don't distinguish between valid &
> invalid values in max_qual->level = 0.  As a person using the driver, I
> don't know if the driver writer _meant_ to put 0 there, to tell me that
> the values the card returns are in dBm, or whether the driver writer
> didn't know _what_ to put there and just left it blank.

	Correct, except that the value will always display as dBm, so
you can at least expect that the author meant dBm, otherwise he would
have put 255.

>  In some ways
> that's a "fix the driver" problem to use IW_QUAL_LEVEL_INVALID, but it
> would be nice to have some way to specify what the card means in the
> levels it returns, either dBm or RSSI.  See the prism54 driver for
> instance, they put a simple SNR in the qual->qual field, and stuff RSSI
> into the qual->level field, yet max_qual->level is left at 0.  This is
> wrong IMHO, but if the RSSI->dBm for the card isn't know, what should
> the correct values in qual->level/qual->noise & max_qual->level be?

	You can always not convert and put 255 in max_qual->level.

> Either cards are going to return dBm (and hence max_qual->level = 0) or
> RSSI (and hence max_qual->level > 0) (if they don't know RSSI->dBm
> conversion tables/values), but at this time we don't know what because
> of the ambiguity surrounding the max_qual->level field.  It would be
> nice to have drivers set this explicitly somewhere...

	Ok, I think I'm convinced. Yes, I should add explicit fields
for that.

> Dan

	Jean