In this post i will be discussing the general concepts of Wi-Fi and Wi-Fi in Android
The contents have been categorised into these sections.
Definition :
WI-FI is a mechanism that allows electronic devices to exchange data wirelessly over a computer network. WI-FI stands for Wireless Fidelity. WI-FI is based on the IEEE 802.11 family of standards and is primarily a Local Area networking (LAN) technology designed to provide in-building broadband coverage.
Modes of Operation :
WI-FI can operate in two different modes
a) Station Mode
b) Access Point mode
Station mode is the default operating mode for a WI-FI adapter. In this mode the adapter operates as a client that connects to a Wi-Fi access point (usually a wi-fi enabled router). This mode is used when you use a wi-fi adapter to connect to a wireless network
In Access Point mode, the adapter will act as an access point enabling other wi-fi adapters to connect to it. So in other words you can use the adapter to create your own wireless network. This can be handy is you want to share a wired Internet connection with other wireless devices and you don't have dedicated access point for example
Working Concepts:
There are three most important items which makes wi-fi working in your laptop or desktop. These are
Radio Signals :
Radio signals are the keys which make WiFi networking possible. These radio signals transmitted from Wi-Fi antennas are picked up by WiFi receivers such as computers and cell phones that are equipped with WiFi cards. Whenever a computer receives any of the signals within the range of a WiFi network which is usually 300-500 feet for antennas, the WiFi card will read the signals and thus create an internet connection between the user and the network without the use of a card.
Wi-Fi Cards :
You can think WiFI card as being an invisible card that connects your computer to the antenna for a direct connection to the internet.
Wi-Fi Hotspots:
A Wi-Fi hotspot is created by installing an access point to an internet connection, The access point transmits a wireless signal over a short distance. Typically covering around 300 feet. When a Wi-Fi enabled device, such as a Pocket PC encounters a hotspot, the device can then connect to that network wirelessly
Wi-Fi in Android
Android uses modified wpa_supplicant daemon for wifi support. On gingerbread versions wpa_supplicant_6 version has used and on ICS versions wpa_supplicant_8 version has been used.
The daemon is controlled through a socket by hardware/libhardware_legacy/wifi/wifi.c (WiFiHW) that gets controlled from Android UI through android.net.wifi pcakage from frameworks/base/wifi/java/android/net/wifi and it's corresponding JNI implementation in frameworks/base/core/jni/android_net_wifi_wifi.cpp. Higher level network management is done in frameworks/base/core/java/android/net.
Original source Link
Android uses a modified wpa_supplicant ( external/wpa_supplicant ) daemon for wifi support which is controlled through a socket by hardware/libhardware_legacy/wifi/wifi.c (WiFiHW) that gets controlled from Android UI through android.net.wifi package from frameworks/base/wifi/java/android/net/wifi/ and it's corresponding jni implementation in frameworks/base/core/jni/android_net_wifi_Wifi.cpp Higher level network management is done in frameworks/base/core/java/android/net
1. Enable building of wpa_supplicant in your BoardConfig.mk
This is by simply adding: BOARD_WPA_SUPPLICANT_DRIVER := WEXT to your BoardConfig.mk . This will set WPA_BUILD_SUPPLICANT to true in external/wpa_supplicant/Android.mk enabling building of driver_wext.c
If you have a custom wpa_supplicant driver (like madwifi or my custom android private commands emulation - see last paragraph) you can replace WEXT with AWEXT or your driver name (MADWIFI, PRISM etc).
2. (Optional) Enable debug for wpa_supplicant.
By default wpa_supplicant is set to MSG_INFO that doesn't tell much.
To enable more messages:
2.1 modify common.c and set wpa_debug_level = MSG_DEBUG
2.2 modify common.h and change #define wpa_printf from if ((level) >= MSG_INFO) to if ((level) >= MSG_DEBUG)
3. Provide a proper wpa_supplicant.conf for your device
Providing a wpa_supplicant.conf it's important because the control socket for android is specified in this file (ctrl_interface= ). This file should be copied by your AndroidBoard.mk to $(TARGET_OUT_ETC)/wifi (usually /system/etc/wifi/wpa_supplicant.conf ). This location will be used on wpa_supplicant service from init.rc.
There are two different ways in which wpa_supplicant can be configured, one is to use a "private" socket in android namespace, created by socket_local_client_connect() function in wpa_ctrl.c and another is by using a standard unix socket.
Minimum required config options in wpa_supplicant.conf :
- Android private socket
ctrl_interface=wlan0
update_config=1
- Unix standard socket
ctrl_interface=DIR=/data/system/wpa_supplicant GROUP=wifi
update_config=1
Depending on your driver you might also want to add:
ap_scan=1
If you have AP association problems with should change to ap_scan=0 to let the driver do the association instead of wpa_supplicant.
If you want to let wpa_supplicant connect to non-WPA or open wireless networks (by default it skips these kind) add:
network={
key_mgmt=NONE
}
4. Have the correct permissions and paths created from init.rc
Incorrect permissions will result in wpa_supplicant not being able to create/open the control socket and libhardware_legacy/wifi/wifi.c won't connect.
Since Google modified wpa_supplicant to run as wifi user/group the directory structure and file ownership should belong to wifi user/group (see os_program_init() function in wpa_supplicant/os_unix.c ).
Otherwise errors like:
E/WifiHW ( ): Unable to open connection to supplicant on "/data/system/wpa_supplicant/wlan0": No such file or directory will appear.
Also wpa_supplicant.conf should belong to wifi user/group because wpa_supplicant will want to modify this file. If your system has /system as read-only use a location like /data/misc/wifi/wpa_supplicant.conf and modify wpa_supplicant service in init.rc with new location.
Make sure the paths are correctly created in init.rc:
mkdir /system/etc/wifi 0770 wifi wifi
chmod 0770 /system/etc/wifi
chmod 0660 /system/etc/wifi/wpa_supplicant.conf
chown wifi wifi /system/etc/wifi/wpa_supplicant.conf
#wpa_supplicant control socket for android wifi.c (android private socket)
mkdir /data/misc/wifi 0770 wifi wifi
mkdir /data/misc/wifi/sockets 0770 wifi wifi
chmod 0770 /data/misc/wifi
chmod 0660 /data/misc/wifi/wpa_supplicant.conf
chown wifi wifi /data/misc/wifi
chown wifi wifi /data/misc/wifi/wpa_supplicant.conf
If you use a Unix standard socket in wpa_supplicant.conf (see above) add:
# wpa_supplicant socket (unix socket mode)
mkdir /data/system/wpa_supplicant 0771 wifi wifi
chmod 0771 /data/system/wpa_supplicant
chown wifi wifi /data/system/wpa_supplicant
Do not add these if you use Android private socket because it will make wpa_supplicant non-functional, because hardware/libhardware_legacy/wifi/wifi.c check for existence of the /data/system/wpa_supplicant folder and will pass a wrong interface name to wpa_ctrl_open() function.
5. Make sure your wpa_supplicant and dhcpcd are starting from init.rc
For wpa_supplicant the init.rc startup like should be depending on which path you chosen:
- Android private socket:
service wpa_supplicant /system/bin/wpa_supplicant -dd -Dwext -iwlan0 -c /system/etc/wifi/wpa_supplicant.conf
socket wpa_wlan0 dgram 660 wifi wifi
group system wifi inet
disabled
oneshot
- Unix standard socket:
service wpa_supplicant /system/bin/wpa_supplicant -dd -Dwext -iwlan0 -c /system/etc/wifi/wpa_supplicant.conf
group system wifi inet
disabled
oneshot
If your wifi driver creates a wifi interface with other name than wlan0 you will have to modify the above line accordingly.
You also should have dhcpcd starting from init.rc
service dhcpcd /system/bin/dhcpcd wlan0
group system dhcp
disabled
oneshot
Newer AOSP versions after Gingerbread use dhcpcd_wlan0 as service name.
6. Provide your driver either as a module or built in kernel and proper kernel support for it.
First make sure that CONFIG_PACKET and CONFIG_NET_RADIO (wireless extensions) are enabled in your kernel. The driver can be built as module (default android way) or built in kernel (if you want to rely in kernel auto probing to support multiple driver eg. USB wifi) but will require source code modifications (see below).
- As kernel module:
Define in your BoardConfig.mk :
1. WIFI_DRIVER_MODULE_PATH := path to the module to be loaded
You need to specify module name in that path too, usually should look something like /system/lib/modules/wlan.ko
2. WIFI_DRIVER_MODULE_NAME:= the name of the network interface that the driver creates, for example wlan0
3. WIFI_DRIVER_MODULE_ARG:= any arguments that you want to pass to the driver on insmod, for example nohwcrypt
Make sure you copy your kernel module when building android to the correct location.
- As built in kernel:
- First init.rc needs to be modified to inform hardware/libhardware_legacy/wifi/wifi.c about the name of the interface, that the driver is already loaded and set the status of wpa_supplicant to running:
setprop wifi.interface "wlan0"
setprop wlan.driver.status "ok"
Do NOT add setprop init.svc.wpa_supplicant "running" as I previously mentioned as it will prevent wpa_supplicant from starting from init.
- Secondly hardware/libhardware_legacy/wifi/wifi.c need to be modified so the functions insmod() and rmmod() return 0 (simply add return 0; as the first line in functions since they are not needed when driver is built in kernel) and return before checking for /proc/modules in check_driver_loaded() function.
You might encounter problems with WifiHW module not being able to connect to wpa_supplicant socket even with the correct permisions. Try to turn off / turn on Wifi from the GUI.
7. Provide a firmware if your driver needs it
If your driver needs a firmware you will have to copy this firmware file to /etc/firmware on your android build. Android doesn't use a standard hotplug binary (although there is an implementation available on android-x86 system/code/toolbox/hotplug.c ) instead the init process takes care of firmware events and loads the firmware file from /etc/firmware (see: system/core/init/devices.c handle_firmware_event() function).
Firmware file name is defined by the driver and might also contain a folder like: RTL8192SU/rtl8192sfw.bin, entire file path should be available in /etc/firmware
8. Make your driver work with Android custom wpa_supplicant commands and SIOCSIWPRIV ioctl.
Android uses SIOCSIWPRIV ioctl to send commands to modify driver behaviour and receive information like signal strength, mac address of the AP, link speed etc. This ioctl is usually not implemented in any known wireless drivers except bcm4329 which is in google msm kernel branch .
The errors from not having this ioctl implemented will look like:
E/wpa_supplicant( ): wpa_driver_priv_driver_cmd failed wpa_driver_priv_driver_cmd RSSI len = 4096
E/wpa_supplicant( ): wpa_driver_priv_driver_cmd failed
D/wpa_supplicant( ): wpa_driver_priv_driver_cmd LINKSPEED len = 4096
E/wpa_supplicant( ): wpa_driver_priv_driver_cmd failed
I/wpa_supplicant( ): CTRL-EVENT-DRIVER-STATE HANGED
After 4, WEXT_NUMBER_SEQUENTIAL_ERRORS errors, android will abort using the device.
To quickly test your wifi from interface you can disable error checking in external/wpa_supplicant/driver_wext.c by simply making ret = 0; in wpa_driver_priv_driver_cmd() function after the SIOCSIWPRIV ioctl call. This will make all access points in android UI appear without signal or MAC address.
To proper implement the ioctl you will need to modify your kernel driver to reply to SIOCSIWPRIV ioctl with RSSI (signal strength) and MACADDR commands being the most important.
A better way is to add a custom driver_xxx.c to google external/wpa_supplicant/ implementing wpa_driver_priv_driver_cmd() function that will take care of RSSI, MACADDR and others, through calls to SIOCGIWSTATS, SIOCGIFHWADDR ioctls, with the rest of the functions being called from driver_wext.c.
Below is a link to a patch for wpa_supplicant that I did for mini-box.com picoPC Android build. It creates a new driver awext which "emulates" android driver commands using wireless extensions ioctls.
How to use the new driver:
1. In your BoardConfig.mk define: BOARD_WPA_SUPPLICANT_DRIVER := AWEXT
2. Change init.rc wpa_supplicant service command line by replacind -Dwext with –Dawext
For Gingerbread patches see the post above.
FAQ's on Wi-Fi on Android
a) I am getting an error "Failed to start supplicant!". How to resolve this issue?
The wpa_supplicant needs to run as a service. It looks like the service entry hasn't been added to init.rc file. Add the below entries to init.rc file.
service wpa_supplicant /system/bin/wpa_supplicant -Dwext -iwlan0 -c/data/misc/wifi/wpa_supplicant.conf
class main
socket wpa_wlan0 dgram 0660 wifi wifi
disabled
oneshot
b) Unable to open connection to supplicant on "/data/system/wpa_supplicant/wlan0": No such file or directory
The socket entry and permissions needs to be added in init.rc file
Add the below entries to init.rc file
mkdir /system/etc/wifi 0770 wifi wifi
chmod 0770 /system/etc/wifi
chmod 0660 /system/etc/wifi/wpa_supplicant.conf
chown wifi wifi /system/etc/wifi/wpa_supplicant.conf
# wpa_supplicant control socket for android wifi.c (android private socket)
mkdir /data/misc/wifi 0770 wifi wifi
mkdir /data/misc/wifi/sockets 0770 wifi wifi
chmod 0770 /data/misc/wifi
chmod 0660 /data/misc/wifi/wpa_supplicant.conf
chown wifi wifi /data/misc/wifi
chown wifi wifi /data/misc/wifi/wpa_supplicant.conf
c) ADDRCONF(NETDEV_UP): wlan0: link is not ready
The wpa_supplicant service is already will be running . But, it's failing to scan the networks. At this point of time, you will receive an warning message like this.
Android uses SIOCSIWPRIV ioctl to send commands to modify driver behaviour and receive information like signal strength, mac address of the AP, link speed etc. This ioctl is usually not implemented. A quick workaround was to emulate this ioctl functionality in WPA_supplicant itself. Here is the corresponding patch Added emulation of Android private ioctls for generic WiFi drivers.
Check this link for the Patch.
d) Wi-Fi is able to scan other networks, but when i tried to connect to other networks, it's getting failed.
The DHCPCD service needs to be started as well. The Dynamic Host Configuration Protocol (DHCP) is a network configuration protocol for hosts on Internet Protocol (IP) networks. This service will provide the dynamic IP.
start the dhcp service from init.rc file
service dhcpcd /system/bin/dhcpcd wlan0
group system dhcp
disabled
oneshot
References
a) http://blog.linuxconsulting.ro/2010/04/porting-wifi-drivers-to-android.html
b) http://www.howstuffworks.com/wireless-network.htm
Let me know, for any broken links
The contents have been categorised into these sections.
- Definition
- Modes of operation
- Working concepts
- WI-FI in Android
- Porting WI-FI drivers to Android
- FAQ's on WI-FI on Android
- References
Definition :
WI-FI is a mechanism that allows electronic devices to exchange data wirelessly over a computer network. WI-FI stands for Wireless Fidelity. WI-FI is based on the IEEE 802.11 family of standards and is primarily a Local Area networking (LAN) technology designed to provide in-building broadband coverage.
Modes of Operation :
WI-FI can operate in two different modes
a) Station Mode
b) Access Point mode
Station mode is the default operating mode for a WI-FI adapter. In this mode the adapter operates as a client that connects to a Wi-Fi access point (usually a wi-fi enabled router). This mode is used when you use a wi-fi adapter to connect to a wireless network
In Access Point mode, the adapter will act as an access point enabling other wi-fi adapters to connect to it. So in other words you can use the adapter to create your own wireless network. This can be handy is you want to share a wired Internet connection with other wireless devices and you don't have dedicated access point for example
Working Concepts:
There are three most important items which makes wi-fi working in your laptop or desktop. These are
- Radio Signals
- Wi-FI Card
- Hotspots which create Wi-Fi network
Radio Signals :
Radio signals are the keys which make WiFi networking possible. These radio signals transmitted from Wi-Fi antennas are picked up by WiFi receivers such as computers and cell phones that are equipped with WiFi cards. Whenever a computer receives any of the signals within the range of a WiFi network which is usually 300-500 feet for antennas, the WiFi card will read the signals and thus create an internet connection between the user and the network without the use of a card.
Wi-Fi Cards :
You can think WiFI card as being an invisible card that connects your computer to the antenna for a direct connection to the internet.
Wi-Fi Hotspots:
A Wi-Fi hotspot is created by installing an access point to an internet connection, The access point transmits a wireless signal over a short distance. Typically covering around 300 feet. When a Wi-Fi enabled device, such as a Pocket PC encounters a hotspot, the device can then connect to that network wirelessly
Wi-Fi in Android
The daemon is controlled through a socket by hardware/libhardware_legacy/wifi/wifi.c (WiFiHW) that gets controlled from Android UI through android.net.wifi pcakage from frameworks/base/wifi/java/android/net/wifi and it's corresponding JNI implementation in frameworks/base/core/jni/android_net_wifi_wifi.cpp. Higher level network management is done in frameworks/base/core/java/android/net.
Original source Link
Porting Wi-Fi drivers
to Android:
Contents
0. Understand how Android WiFi works.
1. Enable building of wpa_supplicant in your BoardConfig.mk
2. (Optional) Enable debug for wpa_supplicant.
3. Provide a proper wpa_supplicant.conf for your device
4. Have the correct paths and permissions created from init.rc
5. Make sure your wpa_supplicant and dhcpcd (optional) are starting from init.rc
6. Provide your driver either as a module or built in kernel and proper kernel support for it and modify Android source code accordingly.
7. Provide a firmware if your module needs it.
8. Make your driver work with Android custom wpa_supplicant commands and SIOCSIWPRIV ioctl
Now onto details.
0. Understand how Android WiFi works.
0. Understand how Android WiFi works.
1. Enable building of wpa_supplicant in your BoardConfig.mk
2. (Optional) Enable debug for wpa_supplicant.
3. Provide a proper wpa_supplicant.conf for your device
4. Have the correct paths and permissions created from init.rc
5. Make sure your wpa_supplicant and dhcpcd (optional) are starting from init.rc
6. Provide your driver either as a module or built in kernel and proper kernel support for it and modify Android source code accordingly.
7. Provide a firmware if your module needs it.
8. Make your driver work with Android custom wpa_supplicant commands and SIOCSIWPRIV ioctl
Now onto details.
0. Understand how Android WiFi works.
Android uses a modified wpa_supplicant ( external/wpa_supplicant ) daemon for wifi support which is controlled through a socket by hardware/libhardware_legacy/wifi/wifi.c (WiFiHW) that gets controlled from Android UI through android.net.wifi package from frameworks/base/wifi/java/android/net/wifi/ and it's corresponding jni implementation in frameworks/base/core/jni/android_net_wifi_Wifi.cpp Higher level network management is done in frameworks/base/core/java/android/net
1. Enable building of wpa_supplicant in your BoardConfig.mk
This is by simply adding: BOARD_WPA_SUPPLICANT_DRIVER := WEXT to your BoardConfig.mk . This will set WPA_BUILD_SUPPLICANT to true in external/wpa_supplicant/Android.mk enabling building of driver_wext.c
If you have a custom wpa_supplicant driver (like madwifi or my custom android private commands emulation - see last paragraph) you can replace WEXT with AWEXT or your driver name (MADWIFI, PRISM etc).
2. (Optional) Enable debug for wpa_supplicant.
By default wpa_supplicant is set to MSG_INFO that doesn't tell much.
To enable more messages:
2.1 modify common.c and set wpa_debug_level = MSG_DEBUG
2.2 modify common.h and change #define wpa_printf from if ((level) >= MSG_INFO) to if ((level) >= MSG_DEBUG)
3. Provide a proper wpa_supplicant.conf for your device
Providing a wpa_supplicant.conf it's important because the control socket for android is specified in this file (ctrl_interface= ). This file should be copied by your AndroidBoard.mk to $(TARGET_OUT_ETC)/wifi (usually /system/etc/wifi/wpa_supplicant.conf ). This location will be used on wpa_supplicant service from init.rc.
There are two different ways in which wpa_supplicant can be configured, one is to use a "private" socket in android namespace, created by socket_local_client_connect() function in wpa_ctrl.c and another is by using a standard unix socket.
Minimum required config options in wpa_supplicant.conf :
- Android private socket
ctrl_interface=wlan0
update_config=1
- Unix standard socket
ctrl_interface=DIR=/data/system/wpa_supplicant GROUP=wifi
update_config=1
Depending on your driver you might also want to add:
ap_scan=1
If you have AP association problems with should change to ap_scan=0 to let the driver do the association instead of wpa_supplicant.
If you want to let wpa_supplicant connect to non-WPA or open wireless networks (by default it skips these kind) add:
network={
key_mgmt=NONE
}
4. Have the correct permissions and paths created from init.rc
Incorrect permissions will result in wpa_supplicant not being able to create/open the control socket and libhardware_legacy/wifi/wifi.c won't connect.
Since Google modified wpa_supplicant to run as wifi user/group the directory structure and file ownership should belong to wifi user/group (see os_program_init() function in wpa_supplicant/os_unix.c ).
Otherwise errors like:
E/WifiHW ( ): Unable to open connection to supplicant on "/data/system/wpa_supplicant/wlan0": No such file or directory will appear.
Also wpa_supplicant.conf should belong to wifi user/group because wpa_supplicant will want to modify this file. If your system has /system as read-only use a location like /data/misc/wifi/wpa_supplicant.conf and modify wpa_supplicant service in init.rc with new location.
Make sure the paths are correctly created in init.rc:
mkdir /system/etc/wifi 0770 wifi wifi
chmod 0770 /system/etc/wifi
chmod 0660 /system/etc/wifi/wpa_supplicant.conf
chown wifi wifi /system/etc/wifi/wpa_supplicant.conf
#wpa_supplicant control socket for android wifi.c (android private socket)
mkdir /data/misc/wifi 0770 wifi wifi
mkdir /data/misc/wifi/sockets 0770 wifi wifi
chmod 0770 /data/misc/wifi
chmod 0660 /data/misc/wifi/wpa_supplicant.conf
chown wifi wifi /data/misc/wifi
chown wifi wifi /data/misc/wifi/wpa_supplicant.conf
If you use a Unix standard socket in wpa_supplicant.conf (see above) add:
# wpa_supplicant socket (unix socket mode)
mkdir /data/system/wpa_supplicant 0771 wifi wifi
chmod 0771 /data/system/wpa_supplicant
chown wifi wifi /data/system/wpa_supplicant
Do not add these if you use Android private socket because it will make wpa_supplicant non-functional, because hardware/libhardware_legacy/wifi/wifi.c check for existence of the /data/system/wpa_supplicant folder and will pass a wrong interface name to wpa_ctrl_open() function.
5. Make sure your wpa_supplicant and dhcpcd are starting from init.rc
For wpa_supplicant the init.rc startup like should be depending on which path you chosen:
- Android private socket:
service wpa_supplicant /system/bin/wpa_supplicant -dd -Dwext -iwlan0 -c /system/etc/wifi/wpa_supplicant.conf
socket wpa_wlan0 dgram 660 wifi wifi
group system wifi inet
disabled
oneshot
- Unix standard socket:
service wpa_supplicant /system/bin/wpa_supplicant -dd -Dwext -iwlan0 -c /system/etc/wifi/wpa_supplicant.conf
group system wifi inet
disabled
oneshot
If your wifi driver creates a wifi interface with other name than wlan0 you will have to modify the above line accordingly.
You also should have dhcpcd starting from init.rc
service dhcpcd /system/bin/dhcpcd wlan0
group system dhcp
disabled
oneshot
Newer AOSP versions after Gingerbread use dhcpcd_wlan0 as service name.
6. Provide your driver either as a module or built in kernel and proper kernel support for it.
First make sure that CONFIG_PACKET and CONFIG_NET_RADIO (wireless extensions) are enabled in your kernel. The driver can be built as module (default android way) or built in kernel (if you want to rely in kernel auto probing to support multiple driver eg. USB wifi) but will require source code modifications (see below).
- As kernel module:
Define in your BoardConfig.mk :
1. WIFI_DRIVER_MODULE_PATH := path to the module to be loaded
You need to specify module name in that path too, usually should look something like /system/lib/modules/wlan.ko
2. WIFI_DRIVER_MODULE_NAME:= the name of the network interface that the driver creates, for example wlan0
3. WIFI_DRIVER_MODULE_ARG:= any arguments that you want to pass to the driver on insmod, for example nohwcrypt
Make sure you copy your kernel module when building android to the correct location.
- As built in kernel:
- First init.rc needs to be modified to inform hardware/libhardware_legacy/wifi/wifi.c about the name of the interface, that the driver is already loaded and set the status of wpa_supplicant to running:
setprop wifi.interface "wlan0"
setprop wlan.driver.status "ok"
Do NOT add setprop init.svc.wpa_supplicant "running" as I previously mentioned as it will prevent wpa_supplicant from starting from init.
- Secondly hardware/libhardware_legacy/wifi/wifi.c need to be modified so the functions insmod() and rmmod() return 0 (simply add return 0; as the first line in functions since they are not needed when driver is built in kernel) and return before checking for /proc/modules in check_driver_loaded() function.
You might encounter problems with WifiHW module not being able to connect to wpa_supplicant socket even with the correct permisions. Try to turn off / turn on Wifi from the GUI.
7. Provide a firmware if your driver needs it
If your driver needs a firmware you will have to copy this firmware file to /etc/firmware on your android build. Android doesn't use a standard hotplug binary (although there is an implementation available on android-x86 system/code/toolbox/hotplug.c ) instead the init process takes care of firmware events and loads the firmware file from /etc/firmware (see: system/core/init/devices.c handle_firmware_event() function).
Firmware file name is defined by the driver and might also contain a folder like: RTL8192SU/rtl8192sfw.bin, entire file path should be available in /etc/firmware
8. Make your driver work with Android custom wpa_supplicant commands and SIOCSIWPRIV ioctl.
Android uses SIOCSIWPRIV ioctl to send commands to modify driver behaviour and receive information like signal strength, mac address of the AP, link speed etc. This ioctl is usually not implemented in any known wireless drivers except bcm4329 which is in google msm kernel branch .
The errors from not having this ioctl implemented will look like:
E/wpa_supplicant( ): wpa_driver_priv_driver_cmd failed wpa_driver_priv_driver_cmd RSSI len = 4096
E/wpa_supplicant( ): wpa_driver_priv_driver_cmd failed
D/wpa_supplicant( ): wpa_driver_priv_driver_cmd LINKSPEED len = 4096
E/wpa_supplicant( ): wpa_driver_priv_driver_cmd failed
I/wpa_supplicant( ): CTRL-EVENT-DRIVER-STATE HANGED
After 4, WEXT_NUMBER_SEQUENTIAL_ERRORS errors, android will abort using the device.
To quickly test your wifi from interface you can disable error checking in external/wpa_supplicant/driver_wext.c by simply making ret = 0; in wpa_driver_priv_driver_cmd() function after the SIOCSIWPRIV ioctl call. This will make all access points in android UI appear without signal or MAC address.
To proper implement the ioctl you will need to modify your kernel driver to reply to SIOCSIWPRIV ioctl with RSSI (signal strength) and MACADDR commands being the most important.
A better way is to add a custom driver_xxx.c to google external/wpa_supplicant/ implementing wpa_driver_priv_driver_cmd() function that will take care of RSSI, MACADDR and others, through calls to SIOCGIWSTATS, SIOCGIFHWADDR ioctls, with the rest of the functions being called from driver_wext.c.
Below is a link to a patch for wpa_supplicant that I did for mini-box.com picoPC Android build. It creates a new driver awext which "emulates" android driver commands using wireless extensions ioctls.
How to use the new driver:
1. In your BoardConfig.mk define: BOARD_WPA_SUPPLICANT_DRIVER := AWEXT
2. Change init.rc wpa_supplicant service command line by replacind -Dwext with –Dawext
For Gingerbread patches see the post above.
FAQ's on Wi-Fi on Android
a) I am getting an error "Failed to start supplicant!". How to resolve this issue?
The wpa_supplicant needs to run as a service. It looks like the service entry hasn't been added to init.rc file. Add the below entries to init.rc file.
service wpa_supplicant /system/bin/wpa_supplicant -Dwext -iwlan0 -c/data/misc/wifi/wpa_supplicant.conf
class main
socket wpa_wlan0 dgram 0660 wifi wifi
disabled
oneshot
b) Unable to open connection to supplicant on "/data/system/wpa_supplicant/wlan0": No such file or directory
The socket entry and permissions needs to be added in init.rc file
Add the below entries to init.rc file
mkdir /system/etc/wifi 0770 wifi wifi
chmod 0770 /system/etc/wifi
chmod 0660 /system/etc/wifi/wpa_supplicant.conf
chown wifi wifi /system/etc/wifi/wpa_supplicant.conf
# wpa_supplicant control socket for android wifi.c (android private socket)
mkdir /data/misc/wifi 0770 wifi wifi
mkdir /data/misc/wifi/sockets 0770 wifi wifi
chmod 0770 /data/misc/wifi
chmod 0660 /data/misc/wifi/wpa_supplicant.conf
chown wifi wifi /data/misc/wifi
chown wifi wifi /data/misc/wifi/wpa_supplicant.conf
c) ADDRCONF(NETDEV_UP): wlan0: link is not ready
The wpa_supplicant service is already will be running . But, it's failing to scan the networks. At this point of time, you will receive an warning message like this.
Android uses SIOCSIWPRIV ioctl to send commands to modify driver behaviour and receive information like signal strength, mac address of the AP, link speed etc. This ioctl is usually not implemented. A quick workaround was to emulate this ioctl functionality in WPA_supplicant itself. Here is the corresponding patch Added emulation of Android private ioctls for generic WiFi drivers.
Check this link for the Patch.
d) Wi-Fi is able to scan other networks, but when i tried to connect to other networks, it's getting failed.
The DHCPCD service needs to be started as well. The Dynamic Host Configuration Protocol (DHCP) is a network configuration protocol for hosts on Internet Protocol (IP) networks. This service will provide the dynamic IP.
start the dhcp service from init.rc file
service dhcpcd /system/bin/dhcpcd wlan0
group system dhcp
disabled
oneshot
References
a) http://blog.linuxconsulting.ro/2010/04/porting-wifi-drivers-to-android.html
b) http://www.howstuffworks.com/wireless-network.htm
Let me know, for any broken links
i am using panda board runs Android ICS and the on board wifi interface is enabled "wlan0"
ReplyDeleteNow i am trying to add another interface "wlan1" to android and i want when i enable the wifi on the GUI it turns on my interface , i have succeeded to do so with wpa_supplicant by setting wifi.interface wlan1 , but the problem is with the DHCP , the DHCP is always trying to run over wlan0 not wlan1
Is there is any property that i can sit to convince the GUI to run the DHCP over wlan1?
Hi Sandeep,
ReplyDeleteThis was a very useful article. I am new to linux programming.
I wanted to know if its possible to enable and disable wifi through IOCTL call from NDK? Also is it possible to identify if the device has wifi feature or not?
Thanks in advance !
It's clear and useful thank you!
ReplyDeleteE/WifiHW ( 1637): Unable to open connection to supplicant on "/data/system/wpa_supplicant/wlan0": Connection refused
ReplyDeleteHi,
ReplyDeletecan you post some article on enabling/disabling wifi within android as well, together, these two utilities will be very useful...