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I am trying to make RaLink RT 5370 WiFi adapter run in dual mode - station as well as AP. I have tiny core linux installed on PI, built on top of 3.18.10 linux kernel version. I have been able to make dual mode work effectively on Atheros based adapter, but the same steps do not work for RT5370. Once PI connects to WiFi through wlan0 interface, I fire the below sequence of commands - 

#1. To create wlan1 in Master mode
iw dev wlan0 interface add wlan1 type __ap

#2. To assign IP to wlan1 interface
ifconfig wlan1 up 192.168.7.1

The above command fails with the error -

ifconfig: SIOCSIFFLAGS: Device or resource busy

and I cannot proceed further. The later steps include bringing up dnsmasq and hostapd.

So, is this driver limitation? And is there a workaround?

deveshchanchlani
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  • See http://raspberrypi.stackexchange.com/questions/40458/can-the-pi-official-wifi-adapter-do-simultaneous-client-ap-modes?rq=1 – Michael Graff Jan 27 '16 at 20:24

1 Answers1

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It looks like your H/W is not providing you a dual-mode. Actually, as my personal experience shows, ONLY 2 or 3 antennas on adapter can give you a POSSIBILITY of running in dual-mode. I saw an USB-dongle, that ACTUALLY supported it, but due to single antenna construction it's perfomance was awful in dual-mode, but very good as just AP or ST.

Alexey Vesnin
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  • But the Atheros wifi adapter for which dual mode worked, has a single antenna. Also, when first command is fired, iwconfig does show 2 interfaces wlan0 on STA mdoe and wlan1 on Master mode. The problem arises when I fire second command. Also, if I set wlan1 on Monitor mode instead of Master mode, even the second command works, but later hostapd fails with the same error message. – deveshchanchlani Jan 26 '16 at 02:48
  • The number of antennas should not matter. It won't be transmitting to multiple destinations at the same time anyway as usually, if it can be both a STA and AP at the same time, the AP portion will be locked to the same frequency the STA side uses. – Michael Graff Jan 26 '16 at 06:44
  • @MichaelGraff it should not - I agree, but IT DOES. If I wouldn't checked it myself I was never write such a thing. It took me a while to figure it out, and it worked – Alexey Vesnin Jan 26 '16 at 14:32
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    Dual antennas does not imply dual radios. This feels antidotal not scientific. – Michael Graff Jan 27 '16 at 05:22
  • @MichaelGraff Antenna sharing between two radios is a BAD idea, as an example you can see a common problem with WiFi+Bluetooth on a single antenna in cheap tablet or phone. Also - I think that a *scientific* explaination of this fact is that 2+ antenna utilizes a MIMO functionality, so one antenna in dual mode works as AP on one channel, and another antenna(s) works as ST on *another* channel, and they are not connected by a contact group, so no interference is occured – Alexey Vesnin Jan 27 '16 at 14:00
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    I never said two radios should share a single antenna. I said two antennas does not imply two radios. – Michael Graff Jan 27 '16 at 14:08
  • Also, you are wrong about what dual antennas gains you for a single radio. It does primary two things: MIMO-style (which uses two antenna 90º out of phase) and diversity, where one antenna receives better than the other for some clients. However, frequently in a diversity arrangement the radio still uses only one antenna to transmit back. So once again, two antennas does not imply any additional radio capacity or functionality. – Michael Graff Jan 27 '16 at 14:10