Subject: Re: 802.11 Transmit power control
To: David Young <>
From: Pavel Cahyna <>
List: tech-net
Date: 10/31/2004 21:56:39

[ please Cc: me while replying ]

>> I still see an issue with it: if the driver *knows* what are the
>> correct units, why shouldn't it provide that information to userland,
>> instead of requiring me to calibrate the card?
> What with manufacturing variation, aging components, and the variety of
> power amps, how does a driver know the correct units?  I feel fairly

The driver knows the units from the datasheet. If the datasheet is
accurate, that's a different and valid question and I must admit that I
have zero experience with it. But if the units are logarithmic (and they
are, at least with the wi hardware), there is some hope that the factors
you named will only multiply the power by a constant, thus only shifting
the value and keeping such operations as "I want decrease the power by 2
dB" meaningful.

What is your experience?

> certain that there is not a driver in NetBSD that can tell us with what
> its transmit power units are with the certainty we need for, say,
> complying with wireless regulations.

How does the manufacturer himself comply with the regulations, given the
influences you named? I'm just curious.

Bye	Pavel