Bringing Wi-Fi Access Point Feature on your embedded board running GNU/Linux

Before reading through this article, to build and install GNU/Linux on embedded board, read through this link.

To bring WiFi client feature on your embedded board, read through this link.
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Follow these simple steps below to bring your board as AP.

1. Install necessary tools
   
   Install hostapd and dnsmasq necessary for an Access Point.

   # apt-get install hostapd dnsmasq --no-install-recommends

2. Configure network interface
   
   Add or modify /etc/network/interface to contain the following.

   # cat /etc/network/interface
   auto lo wlan0
   iface lo inet loopback
   allow-hotplug eth0
   iface eth0 inet dhcp
   
   iface wlan0 inet static
   address 192.168.1.1
   network 192.168.1.0
   netmask 255.255.255.0
   allow-hotplug wlan0

   The above file says how our system get connected through eth0, wlan0 and lo. Check man page of interfaces for more details.
3. Configure hostapd
   

   # cat /etc/default/hostapd
   DAEMON_CONF="/etc/hostapd/hostapd.conf"
   DAEMON_OPTS="-dd"

   # cat /etc/hostapd/hostapd.conf
   interface=wlan0
   driver=nl80211
   ssid=zilogic
   channel=1

4. Configure dnsmasq with Client IP range
   

   # cat /etc/dnsmasq.conf
   
   interface=wlan0
   dhcp-range=192.168.1.10,192.168.1.100,12h
   dhcp-option=3,192.168.1.1

5. Start hostapd and dnsmasq services.
   

   # service hostapd start
   # service dnsmasq start

Note: Now, you can try Raspberry Pi 3 that comes with WiFi and Bluetooth on-board for IoT applications.

More Reading

1. What is the significance of firmware-atheros package?
   
2. What is the significance of wireless-tools utility?
   
3. What is iw and iwconfig? How do they differ?
   
4. What is wpa_supplicant? How to connect to an encrypted connection?
   
5. What is Wireless Extensions(WE)?
   
6. What are nl80211 and cfg80211 and how do they differ from WE?
   
7. What is Bridging in network connections? 

Bringing Wi-Fi Client Feature on your Embedded board running GNU/Linux

To prepare your embedded board with GNU/Linux running on it, read through this link.

To bring Wi-Fi  Access Point feature, read through this link.
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To bring Wi-Fi client feature with the given NIC on your Embedded board running Linux, we may need

1. Device driver for the given NIC enabled in the Kernel.
   
2. Some HAL layer firmware, if required by the device driver. (Ref. ath9k_htc firmware - github.com)
3. Certain utilities to configure and manage Wi-Fi.
   
   (iw, ip, iwconfig, wpa_passphrase, wpa_supplicant, firmware-atheros)

Installing custom packages

You may require some software utilities like, iwconfig, iw, etc., which may be required to solve your purpose. To install them there are the following possibilities.

1. Download .deb packages of required utilities to a USB Stick or to the SD Card and install them using dpkg with -i option. But, we have to know all the dependencies for evey package you install and have them downloaded and installed prior to installing the main package.
   
2. Include the packages while building the rootfs.
   
3. Connect to internet through any possible interface available (ethernet, wlan) and using apt-get install them from your favorite repository. But, your board should have any such interface enabled and available for use.
   
4. Use chroot on your host Linux System to change from the host’s rootfs to the SD Cards rootfs/(target fs). This method is followed in this case.
   

Installing custom packages using chroot

• This requires super user access. VirtualBox together with Vagrant can be used to get super user access by normal user.
• Also, chroot will work only if the target architecture is same as that of the host.
  1. When configuring kernel during compilation, enable support for ath9k_htc under device drivers in menuconfig. ath9k_htc is a device driver specific to atheros AR9271 which is the chipset used in our given NIC (TP-Link TL-WN722N).
     
  2. qemu-arm-static is a binary that can be installed in host and copied to target file system. This is used as an interpreter to run arm binaries of target file system(SD Card rootfs/). This will fix the architecture issue while using chroot.
     

     $ sudo apt-get install binfmt-support qemu-user-static
     $ cp /usr/bin/qemu-arm-static /home/user/rootfs/usr/bin

     Here, SD Card is mounted at /home/user/. The option binfmt-support says the binfmt_misc kernel module to use qemu-arm-static as the interpreter to execute arm binaries.
  3. Mount proc/ and sys/
     

     $ cd rootfs
     $ sudo mount -t proc none proc/
     $ sudo mount -t sysfs sysfs sys/
     $ sudo mount -o bind /dev dev/

  4. Change rootfs (need to be super user to do this)
     

     $ sudo chroot rootfs/
     root@emdebian:/#

  5. Update list and install packages (firmware-atheros, wireless-tools, wpasupplicant, wireless-tools, iw, kmod) and then exit and unmount proc, sys and dev. firmware-atheros is required for our case but not mandatory for all the atheros devices[3].
     

     # apt-get update
     # apt-get install firmware-atheros wpasupplicant wireless-tools iw kmod
     # exit
     $ unmount /rootfs/proc/
     $ unmount /rootfs/sys/

     Unmount the SD Card from the PC and connect to the board and boot it. In SAMA5D3_Xplained board, a dedicated DEBUG console is provided which can be used to connect to system terminal through a USB-Serial converter. After the system boots up and logged in, plug the NIC in the USB port. The device should be automatically detected and will be ready to use.
  6. Enable wlan0
     

     # ifconfig           /* To check if wlan inteface is listed */
     # ifconfig wlan0 up

     The second command will enable the default WLAN interface wlan0. Now the interface will be up and ready to use.

Connecting to an open network as Client

1. Connecting to an open network is simple. It can be achieved using the iwconfig utility.
   

   # iwconfig dev wlan0 connect <SSID>

   You can also try iw.
2. Get IP assigned from AP
   

   # dhclient wlan0

   You can check -r option for dhclient to release the current IP lease when necessary.

More Reading

1. What is the significance of firmware-atheros package?
   
2. What is the significance of wireless-tools utility?
   
3. What is iw and iwconfig? How do they differ?
   
4. What is wpa_supplicant[4]? How to connect to an encrypted connection?
   
5. What is Wireless Extensions(WE)?
   
6. What are nl80211 and cfg80211 and how do they differ from WE?
   
7. What is Bridging in network connections?