Tx power conttrol issue

Jouni Malinen jkmaline at cc.hut.fi
Fri Aug 1 22:24:58 EDT 2003

On Fri, Aug 01, 2003 at 09:20:12PM +0200, Jirka Bohac wrote:

> Yes, up to 0.0.3, txpower can be controlled directly with "iwconfig xxx
> txpower". However, there are a couple of problems. The setting does not
> remain in effect after a "card reset", which is performed from time to
> time by the driver. So after the first reset, the power is back on "auto".

> Maybe it's because of these problems that Jouni disabled the txpower
> control support. He also says that the setting is not accurate - indeed,
> the "decibells" you use in iwconfig have NOTHING TO DO with real output
> power expressed in dBm. Jouni probably wants to use a special prism
> power feedback register, CR58, for more accurate setting.

No, removal of txpower command has nothing to do with either of these
issues. First one can be fixed easily and accuracy is not that much of a
problem. Just read the v0.0.4 entry in ChangeLog for the real reason.

> However, in our network where most people use the same kind of card, we
> have our own calibrations, and we learned to live with the old system.
> The absence of txpower control in 0.0.4 is a big pain for us :( 
> Anything would be better than nothing at all.

It's not like "nothing at all"; Prism2/2.5/3 cards have TX power control
in the firmware. Host AP driver has always defaulted to let the firmware
take care of TPC. Newer firmware versions include a command for limiting
maximum power, but Host AP driver does not yet support it.

> 	Is any help needed to get txpower control back in the driver?

I will probably take a look at implementing proper feedback loop from
the TX power measurements. However, I do not know when I will have time
for doing this. Clean and tested patch to implement this would be
accepted gladly ;-).

Jouni Malinen                                            PGP id EFC895FA

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