[rt2x00-users] rt2800usb and automatic channel selection

Tuomas Räsänen tuomasjjrasanen at opinsys.fi
Mon Dec 15 23:24:01 AEDT 2014

On 12/15/2014 01:52 PM, Johannes Stezenbach wrote:
> On Mon, Dec 15, 2014 at 11:25:35AM +0100, Sven Neumann wrote:
>> we are trying to use hostapd with a rt2800usb device. This works
>> fine so far, but we have found that the automatic channel
>> selection feature of hostapd (see
>> http://wireless.kernel.org/en/users/Documentation/acs) doesn't
>> work properly. This is because the survey based algorithm relies
>> on the nl80211 survey API command to  query the interface for
>> channel active time, channel busy time, channel  tx time and
>> noise It appears that the rt2800 drivers implement the
>> get_survey command, but it is are not filling in infomation
>> about the noise floor. Now I wonder if there is a chance that
>> this information is somehow available in the driver and whether
>> the get_survey command could be changed to also provide
>> information about the noise floor on a specific channel. Any
>> help with that would be much appreciated.

We have an identical use-case and have implemented a really-poor-man's 
automatic channel selection on *top* of hostapd. However, I'd be 
interested in implementing/testing/helping to implement necessary bits 
to the driver (if it is even supported by the hardware).

> Probably I remember it wrong because it is a long time
> since I did a bit of work on rt2800usb (2011), but I
> think there is no documentation available for the
> baseband processor registers, thus the usual advice
> is to download the vendor driver for your particular
> hardware and check if it implements it, and then port
> it to rt2x00. But I think the vender drivers do not implement
> AP mode, so it is likely that the function you need is
> not available.
> http://www.mediatek.com/en/downloads/
> Anyway, maybe you can give more details on the device you want to use.

We have been using these:

Bus 001 Device 004: ID 148f:3070 Ralink Technology, Corp. RT2870/RT3070 
Wireless Adapter
Bus 001 Device 003: ID 0b05:179d ASUSTek Computer, Inc. USB-N53 
802.11abgn Network Adapter [Ralink RT3572]

> Generally I'm not sure how well the rt2800 USB devices work for
> AP mode vs. the PCI devices, IIRC the USB interface has
> some limitation for getting the TX status of each
> sent packets, and issues for implementing power save
> (though that might not affect AP mode).  So while it may
> basically work it might not be fit for production use.
> I hope I'm not spreading FUD, maybe someone else from rt2x00
> team can confirm or object since my knowledge is basically
> from 2011.

AP mode with rt2800 USB devices work just fine, we have been using them 
in production for years.


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