RPi Peripherals

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Setup examples for various peripherals

Wireless: TP-Link TL-WN722N USB wireless adapter (Debian 6)

See also:



This will serve as a general guide for USB wireless devices but may need modifying for your specific one.

  • Edit /etc/apt/sources.list to add the non-free archive and backports (eg: sudo vi /etc/apt/sources.list):
 deb http://ftp.us.debian.org/debian/ squeeze main non-free
 deb http://security.debian.org/ squeeze/updates main non-free
 deb http://ftp.us.debian.org/debian/ squeeze-updates main non-free
 deb http://backports.debian.org/debian-backports squeeze-backports main non-free
  • Update the package cache:
 sudo apt-get update
  • Download the wifi utils:
 sudo apt-get install wireless-tools usbutils 
  • Download the required firmware and put it in the correct location - you may not need to do this for your adapter or you may need different firmware - see below.
 sudo apt-get install firmware-atheros
 sudo wget http://linuxwireless.org/download/htc_fw/1.3/htc_9271.fw
 sudo cp htc_9271.fw /lib/firmware
  • Add adapter definition to network config - eg: sudo vi /etc/network/interfaces - add the wlan0 section:
# Used by ifup(8) and ifdown(8). See the interfaces(5) manpage or
# /usr/share/doc/ifupdown/examples for more information.

auto lo

iface lo inet loopback
iface eth0 inet dhcp

# The wireless interface
auto wlan0
iface wlan0 inet dhcp
wpa-conf /etc/wpa.conf
  • Plug in adapter
  • Confirm adapter is present:
 root@raspberrypi:~# iwconfig
  lo        no wireless extensions.

  eth0      no wireless extensions.

  wlan0     IEEE 802.11bgn  ESSID:off/any
            Mode:Managed  Access Point: Not-Associated   Tx-Power=20 dBm
            Retry  long limit:7   RTS thr:off   Fragment thr:off
            Encryption key:off
            Power Management:off
  • Scan your network to see what wireless access points can be seen. You may need to do this to identify your network's SSID (name), but it also confirms that the wifi dongle is doing something. The first command just lists the SSIDs found, the second tells you probably more than you ever want to know:
  sudo iwlist wlan0 scan | grep ESSID


  sudo iwlist wlan0 scan
  • Create the wpa.conf file - eg: sudo vi /etc/wpa.conf:

Note: The ssid is case sensitive - if your WLAN's SSID is MYLAN, using "mylan" will not work - you won't connect!

pairwise=CCMP TKIP
  • Start the adapter
  sudo ifup wlan0
  • Double-check whether you are connected - below the WLAN interface has been given an IP address - looks good!
 root@raspberrypi:~# ifconfig
 eth0      Link encap:Ethernet  HWaddr b8:27:eb:76:7e:2e
           inet addr:  Bcast:  Mask:
           RX packets:1060 errors:0 dropped:0 overruns:0 frame:0
           TX packets:146 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:95749 (93.5 KiB)  TX bytes:48493 (47.3 KiB)

 lo        Link encap:Local Loopback
           inet addr:  Mask:
           UP LOOPBACK RUNNING  MTU:16436  Metric:1
           RX packets:8 errors:0 dropped:0 overruns:0 frame:0
           TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:560 (560.0 B)  TX bytes:560 (560.0 B)

 wlan0     Link encap:Ethernet  HWaddr b0:48:7a:91:5c:f4
           inet addr:  Bcast:  Mask:
           RX packets:31 errors:0 dropped:0 overruns:0 frame:0
           TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:2260 (2.2 KiB)  TX bytes:1542 (1.5 KiB)

If you are now connected, well done! If not, check your editing and also have a look at the output of dmesg to see if you have any error messages. You can also view the system log for messages - for example: sudo cat /var/log/messages | more


USB interrupt/dma system debug messages

Firing up the TP-Link USB WLAN interface generates a lot of debug messages in the system log like this:

DEBUG:handle_hc_chhltd_intr_dma:: XactErr without NYET/NAK/ACK

Things may calm down a bit if the following file is created in /etc/modprobe.d (eg: sudo vi /etc/modprobe.d/smscnonturbo.conf) and then the RPi rebooted:


 options smsc95xx turbo_mode=N

This fix may slow down wired LAN performance but help with wireless and reduce the frequency of the debug messages - YMMV. If you want to undo this fix, just delete the file (sudo rm /etc/modprobe.d/smscnonturbo.conf) and reboot.

Firmware requirements

If no wlanx device is shown, you might need to download firmware for your USB wifi device (or track down other compatible drivers if they are available). To confirm this, check the dmesg output when you plug in your adapter - typing dmesg at the command prompt may be sufficient - and look for information related to your adapter - the example dmesg output below shows what is seen in the event of the TP-Link firmware not being present - notice that the name of the required firmware file is given (htc_9271.fw), the driver name (ath9k_htc) and an error -22 message:

  usb 1- ath9k_htc: Firmware - htc_9271.fw not found
  ath9k_htc: probe of 1- failed with error -22
  usbcore: registered new interface driver ath9k_htc

Armed with this information, try a web search for 'debian 6' and the name of the driver or driver file and/or head over to http://linuxwireless.org. Also check the links at the top of this page.

Power requirements

If you experience erratic network, keyboard, mouse or Raspberry Pi operation when using a USB wifi dongle, check that whatever is powering your RPi and/or USB hub can deliver sufficient current for everything that's connected together. The first setup tried with the TP-Link adapter had it, a keyboard, mouse and the RPi all connected to a Trust 7-port powered USB hub with a 5V 2A power supply, but in this configuration the mouse stopped working. In this case, the fix was to power the RPi from a separate 5V 1A phone power adapter.