硬件：IMX6的arm板、树莓派 Raspberry Pi 无线USB网卡 EDUP EP-N8508GS 黄金版 免驱，并且已经带了驱动

关于wifi连接可以看 https://blog.csdn.net/chenjk10/article/details/90521093

• 普通热点

开启普通热点，只有一个无线网卡，无法上网的热点

# 如果启动了wpa_supplicant，先要停止
killall wpa_supplicant > /dev/null 2>&1
# 在停止了wpa_supplicant后，关联的网卡会被变成禁用状态
# 注意：如果使用代码停止wpa_supplicant，需要休眠等待一下，要等待wpa_supplicant真的退出并且网卡状态变化

修改或者创建hostapd.conf文件，这个文件一般在/etc/hostapd.conf

##### hostapd configuration file ##############################################

interface=wlan0
ctrl_interface=/var/run/hostapd

ssid=MyAPName

# Channel number (IEEE 802.11)
# (default: 0, i.e., not set)
# Please note that some drivers do not use this value from hostapd and the
# channel will need to be configured separately with iwconfig.
#
# If CONFIG_ACS build option is enabled, the channel can be selected
# automatically at run time by setting channel=acs_survey or channel=0, both of
# which will enable the ACS survey based algorithm.
channel=6

# Enable WPA. Setting this variable configures the AP to require WPA (either
# WPA-PSK or WPA-RADIUS/EAP based on other configuration). For WPA-PSK, either
# wpa_psk or wpa_passphrase must be set and wpa_key_mgmt must include WPA-PSK.
# Instead of wpa_psk / wpa_passphrase, wpa_psk_radius might suffice.
# For WPA-RADIUS/EAP, ieee8021x must be set (but without dynamic WEP keys),
# RADIUS authentication server must be configured, and WPA-EAP must be included
# in wpa_key_mgmt.
# This field is a bit field that can be used to enable WPA (IEEE 802.11i/D3.0)
# and/or WPA2 (full IEEE 802.11i/RSN):
# bit0 = WPA
# bit1 = IEEE 802.11i/RSN (WPA2) (dot11RSNAEnabled)
wpa=2

# WPA pre-shared keys for WPA-PSK. This can be either entered as a 256-bit
# secret in hex format (64 hex digits), wpa_psk, or as an ASCII passphrase
# (8..63 characters) that will be converted to PSK. This conversion uses SSID
# so the PSK changes when ASCII passphrase is used and the SSID is changed.
# wpa_psk (dot11RSNAConfigPSKValue)
# wpa_passphrase (dot11RSNAConfigPSKPassPhrase)
#wpa_psk=0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
wpa_passphrase=12345678

# Set of accepted key management algorithms (WPA-PSK, WPA-EAP, or both). The
# entries are separated with a space. WPA-PSK-SHA256 and WPA-EAP-SHA256 can be
# added to enable SHA256-based stronger algorithms.
# (dot11RSNAConfigAuthenticationSuitesTable)
#wpa_key_mgmt=WPA-PSK WPA-EAP
wpa_key_mgmt=WPA-PSK

# Set of accepted cipher suites (encryption algorithms) for pairwise keys
# (unicast packets). This is a space separated list of algorithms:
# CCMP = AES in Counter mode with CBC-MAC [RFC 3610, IEEE 802.11i/D7.0]
# TKIP = Temporal Key Integrity Protocol [IEEE 802.11i/D7.0]
# Group cipher suite (encryption algorithm for broadcast and multicast frames)
# is automatically selected based on this configuration. If only CCMP is
# allowed as the pairwise cipher, group cipher will also be CCMP. Otherwise,
# TKIP will be used as the group cipher.
# (dot11RSNAConfigPairwiseCiphersTable)
# Pairwise cipher for WPA (v1) (default: TKIP)
wpa_pairwise=TKIP CCMP
#wpa_pairwise=CCMP
# Pairwise cipher for RSN/WPA2 (default: use wpa_pairwise value)
#rsn_pairwise=CCMP
rsn_pairwise=CCMP TKIP
#rsn_pairwise=CCMP

# Time interval for rekeying GTK (broadcast/multicast encryption keys) in
# seconds. (dot11RSNAConfigGroupRekeyTime)
#wpa_group_rekey=600
#wpa_group_rekey=86400

# auto add current network card into bridge
#bridge=br0

# IEEE 802.11 specifies two authentication algorithms. hostapd can be
# configured to allow both of these or only one. Open system authentication
# should be used with IEEE 802.1X.
# Bit fields of allowed authentication algorithms:
# bit 0 = Open System Authentication
# bit 1 = Shared Key Authentication (requires WEP)
#auth_algs=3

##### Wi-Fi Protected Setup (WPS) #############################################

eap_server=1

# WPS state
# 0 = WPS disabled (default)
# 1 = WPS enabled, not configured
# 2 = WPS enabled, configured
wps_state=2

uuid=12345678-9abc-def0-1234-56789abcdef0

# Device Name
# User-friendly description of device; up to 32 octets encoded in UTF-8
device_name=RTL8192CU

# Manufacturer
# The manufacturer of the device (up to 64 ASCII characters)
manufacturer=Realtek

# Model Name
# Model of the device (up to 32 ASCII characters)
model_name=RTW_SOFTAP

# Model Number
# Additional device description (up to 32 ASCII characters)
model_number=WLAN_CU

# Serial Number
# Serial number of the device (up to 32 characters)
serial_number=12345

# Primary Device Type
# Used format: <categ>-<OUI>-<subcateg>
# categ = Category as an integer value
# OUI = OUI and type octet as a 4-octet hex-encoded value; 0050F204 for
#       default WPS OUI
# subcateg = OUI-specific Sub Category as an integer value
# Examples:
#   1-0050F204-1 (Computer / PC)
#   1-0050F204-2 (Computer / Server)
#   5-0050F204-1 (Storage / NAS)
#   6-0050F204-1 (Network Infrastructure / AP)
device_type=6-0050F204-1

# OS Version
# 4-octet operating system version number (hex string)
os_version=01020300

# Config Methods
# List of the supported configuration methods
config_methods=label display push_button keypad

##### default configuration #######################################

driver=rtl871xdrv
beacon_int=100
# Operation mode (a = IEEE 802.11a, b = IEEE 802.11b, g = IEEE 802.11g,
# ad = IEEE 802.11ad (60 GHz); a/g options are used with IEEE 802.11n, too, to
# specify band)
# Default: IEEE 802.11b
hw_mode=g
ieee80211n=1
wme_enabled=1
ht_capab=[SHORT-GI-20][SHORT-GI-40][HT40+]
max_num_sta=8

部分配置说明

# 设置使用的网卡
interface=wlan0
# 配置热点名称
ssid=MyAPName
# 热点支持的加密类型，
# bit0 = WPA
# bit1 = IEEE 802.11i/RSN (WPA2) (dot11RSNAEnabled)
wpa=2
# 热点加密类型
wpa_key_mgmt=WPA-PSK
# 热点密码
wpa_passphrase=12345678
# 接受的密匙类型
wpa_pairwise=TKIP CCMP
rsn_pairwise=CCMP TKIP

官方配置文件：http://w1.fi/cgit/hostap/plain/hostapd/hostapd.conf

热点要使用DHCP功能，所以还要配置DHCP配置文件，使用是udhcpd，配置文件在/etc/udhcpd.conf

如果使用静态IP地址也可以不使用DHCP

# Sample udhcpd configuration file (/etc/udhcpd.conf)

# The start and end of the IP lease block

start       192.168.0.150   #default: 192.168.0.20
end     192.168.0.240   #default: 192.168.0.254

# The interface that udhcpd will use
interface    wlan0    #default: eth0

# The maximim number of leases (includes addressesd reserved
# by OFFER's, DECLINE's, and ARP conficts

max_leases  21      #default: 254

# If remaining is true (default), udhcpd will store the time
# remaining for each lease in the udhcpd leases file. This is
# for embedded systems that cannot keep time between reboots.
# If you set remaining to no, the absolute time that the lease
# expires at will be stored in the dhcpd.leases file.

#remaining  yes     #default: yes

# The time period at which udhcpd will write out a dhcpd.leases
# file. If this is 0, udhcpd will never automatically write a
# lease file. (specified in seconds)

#auto_time  7200        #default: 7200 (2 hours)

# The amount of time that an IP will be reserved (leased) for if a
# DHCP decline message is received (seconds).

#decline_time   3600        #default: 3600 (1 hour)

# The amount of time that an IP will be reserved (leased) for if an
# ARP conflct occurs. (seconds

#conflict_time  3600        #default: 3600 (1 hour)

# How long an offered address is reserved (leased) in seconds

#offer_time 60      #default: 60 (1 minute)

# If a lease to be given is below this value, the full lease time is
# instead used (seconds).

#min_lease  60      #defult: 60

# The location of the leases file

#lease_file /var/lib/misc/udhcpd.leases #defualt: /var/lib/misc/udhcpd.leases

# The location of the pid file
#pidfile    /var/run/udhcpd.pid #default: /var/run/udhcpd.pid

# Everytime udhcpd writes a leases file, the below script will be called.
# Useful for writing the lease file to flash every few hours.

#notify_file                #default: (no script)

#notify_file    dumpleases  # <--- usefull for debugging

# The following are bootp specific options, setable by udhcpd.

#siaddr     192.168.0.22        #default: 0.0.0.0

#sname      zorak           #default: (none)

#boot_file  /var/nfs_root       #default: (none)

# The remainer of options are DHCP options and can be specifed with the
# keyword 'opt' or 'option'. If an option can take multiple items, such
# as the dns option, they can be listed on the same line, or multiple
# lines. The only option with a default is 'lease'.

#Examles
opt dns 116.116.116.116
option  subnet  255.255.255.0
opt router  192.168.0.1
#opt    wins    192.168.10.10
option  dns 129.219.13.81   # appened to above DNS servers for a total of 3
option  domain  local
option  lease   864000      # 10 days of seconds

# Currently supported options, for more info, see options.c
#opt subnet
#opt timezone
#opt router
#opt timesvr
#opt namesvr
#opt dns
#opt logsvr
#opt cookiesvr
#opt lprsvr
#opt bootsize
#opt domain
#opt swapsvr
#opt rootpath
#opt ipttl
#opt mtu
#opt broadcast
#opt wins
#opt lease
#opt ntpsrv
#opt tftp
#opt bootfile

# Static leases map
#static_lease 00:60:08:11:CE:4E 192.168.0.54
#static_lease 00:60:08:11:CE:3E 192.168.0.44

部分参数说明：

# 使用的无线网卡
interface    wlan0
# IP池范围
start       192.168.0.100
end     192.168.0.240
# 路由地址
opt router  192.168.0.1

官方配置文件说明：https://udhcp.busybox.net/udhcpd.conf

开始配置热点：

# 启用网卡
ifconfig wlan0 up
# 给无线网卡设置IP地址
ifconfig wlan0 192.168.0.1
# 启动DHCP，必须先设置无线网卡地址，不然启动udhcp会失败
udhcpd /etc/udhcpd.conf 
# 启动热点
hostapd /etc/hostapd.conf -B

桥接方式建立热点

配置文件和上面的一样，这里桥接的是以太网卡eth0。

# 设置两个网卡IP为0.0.0.0
ifconfig eth0 0.0.0.0
ifconfig wlan0 0.0.0.0
# 如果网桥已经存在则删除
brctl delbr br0 >/dev/null 2>&1
# 新建网桥br0
brctl addbr br0
# Stop STP(spanning tree protocol, this protocol seems to prevent the network from generating loops, because the self-defined network, there should be no loop, this protocol can be stopped)
brctl stp br0 off
# 添加无线网卡和以太网卡到网桥br0中
brctl addif br0 wlan0
brctl addif br0 eth0
# Set the bridge forwarding delay time
brctl setfd br0 0
# 设置网桥静态IP地址
ifconfig br0 192.168.1.205 netmask 255.255.255.0
# 查看当前网桥配置
brctl show

# 启动hostapd
hostapd /etc/hostapd.conf -B
# 给无线网卡设置IP地址，这个和udhcpd.conf中配置的路由地址一样
ifconfig wlan0 192.168.0.1
# 启动udhcpd, 必须先设置wlan0的IP地址，不然这步会失败
udhcpd /etc/udhcpd.conf 

感觉上面有些步骤似乎是多余的，桥接eth0后，连通了eth0的路由，实际上似乎也是使用eth0连接的外部路由的DHCP，arm板上似乎也没必要开DHCP服务。

启动热点后，连接并使用热点可能会有错误br0: received packet on eth0 with own address as source address，看了一下网桥br0和eth0的MAC地址是一样的，估计br0是复制了eth0的MAC地址，这里需要修改eth0的MAC地址，修改br0的MAC地址似乎还是继续报错，修改命令为：

ifconfig eth0 hw ether dc:07:c1:00:ed:BB

尝试了一下，去掉udhcpd部分，修改成如下：

# 设置两个网卡IP为0.0.0.0
ifconfig eth0 0.0.0.0
ifconfig wlan0 0.0.0.0
# 如果网桥已经存在则删除
brctl delbr br0 >/dev/null 2>&1
# 新建网桥br0
brctl addbr br0
# Stop STP(spanning tree protocol, this protocol seems to prevent the network from generating loops, because the self-defined network, there should be no loop, this protocol can be stopped)
brctl stp br0 off
# 添加无线网卡和以太网卡到网桥br0中
brctl addif br0 wlan0
brctl addif br0 eth0
# Set the bridge forwarding delay time
brctl setfd br0 0
# 启用网桥
ifconfig br0 up
# 查看当前网桥配置
brctl show

# 启动hostapd
hostapd /etc/hostapd.conf -B
# 由于没有设置静态IP，这里使用udhcpc更新IP地址和DNS
# -n    Exit with failure if lease is not immediately obtained
udhcpc -i br0 -n

完成后使用ifconfig显示的网卡配置为，可以正常连接热点上网

br0       Link encap:Ethernet  HWaddr dc:07:c1:00:ed:85  
          inet addr:192.168.1.62  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1274 errors:0 dropped:0 overruns:0 frame:0
          TX packets:13 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:65848 (64.3 KiB)  TX bytes:1590 (1.5 KiB)

eth0      Link encap:Ethernet  HWaddr dc:07:c1:00:ed:85  
          inet6 addr: fe80::de07:c1ff:fe00:ed85/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:4801 errors:0 dropped:0 overruns:0 frame:0
          TX packets:271 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:395515 (386.2 KiB)  TX bytes:44022 (42.9 KiB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:9 errors:0 dropped:0 overruns:0 frame:0
          TX packets:9 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:612 (612.0 B)  TX bytes:612 (612.0 B)

wlan0     Link encap:Ethernet  HWaddr e8:4e:06:6f:87:dc  
          inet6 addr: fe80::ea4e:6ff:fe6f:87dc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:240 errors:0 dropped:7 overruns:0 frame:0
          TX packets:1113 errors:0 dropped:7 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:183837 (179.5 KiB)  TX bytes:161991 (158.1 KiB)

下面是一个arm上的脚本，用于启动wifi热点，原来有个脚本不过有些问题，我修改了一下

#!/bin/sh

# Check that the /etc/udhcpd.conf file exists and can be executed
if [ ! -x /usr/sbin/hostapd ]
then
    echo "/usr/sbin/hostapd no exist or can't execute"
    exit 0
fi

# check network card wlanX
ifconfig -a|grep wlan > /dev/null
if [[ $? -ne 0 ]]
then
    echo no device wlanX
    exit 0
fi
# Gets the full name of the wlan and assigns it to wlanx
wlanx=`ifconfig -a|grep wlan|awk '{print $1}'`
if [[ $? -ne 0 ]]
then
    echo failed to get device wlanX name
    exit 0
fi

# Check that the /etc/hostapd.conf file exists and can be write
if [ ! -w /etc/hostapd.conf ]
then
    echo "/etc/hostapd.conf no exist or can't write"
    exit 0
fi

# Check that the /etc/udhcpd.conf file exists and can be write
if [ ! -w /etc/udhcpd.conf ]
then
    echo "/etc/udhcpd.conf no exist or can't write"
    exit 0
fi

# network card configure file: /etc/network/interfaces
#busybox sed -i "s/eth0/br0/g" /etc/network/interfaces
#busybox sed -i "s/auto wlan0/#auto wlan0/g" /etc/network/interfaces
#busybox sed -i "s/iface wlan0 inet dhcp/#iface wlan0 inet dhcp/g" /etc/network/interfaces

# check command
if [ "$1" != "start" -a "$1" != "stop" -a "$1" != "restart" ]
then
    echo paramter error.only accept start/stop/restart.
fi

# Close all related programs
if [ "$1" = "stop" -o "$1" = "restart" -o "$1" = "start" ]
then                                                                            
    echo "Stopping the hostapd and udhcpd and wpa_supplicant : "
    killall hostapd >/dev/null 2>&1
    killall udhcpd >/dev/null 2>&1
    killall wpa_supplicant > /dev/null 2>&1
fi

if [ "$1" = "start" -o "$1" = "restart" ]
then
    # /etc/hostapd.conf
    echo "Starting the hostapd and udhcpd : "
    wlan_old=`cat /etc/hostapd.conf|grep '^interface'`
    wlan_new="interface="$wlanx
    busybox sed -i "s/$wlan_old/$wlan_new/g" /etc/hostapd.conf

    # /etc/udhcpd.conf
    #wlan_old=`cat /etc/udhcpd.conf|grep '^interface'`
    #wlan_new="interface    "$wlanx"    #default: eth0"
    #busybox sed -i "s/$wlan_old/$wlan_new/g" /etc/udhcpd.conf

    #start bridge eth0
    ifconfig eth0 0.0.0.0
    ifconfig $wlanx 0.0.0.0
    ifconfig $wlanx up
    # Delete possible Bridges
    brctl delbr br0 >/dev/null 2>&1
    # add new bridge br0
    brctl addbr br0
    # Stop STP(spanning tree protocol, this protocol seems to prevent the network from generating loops, because the self-defined network, there should be no loop, this protocol can be stopped)
    brctl stp br0 off
    # Add the port eth0 and the wireless port to the bridge
    brctl addif br0 $wlanx
    brctl addif br0 eth0
    # Set the bridge forwarding delay time
    brctl setfd br0 0
    # set static ip addr
    #ifconfig br0 192.168.1.205 netmask 255.255.255.0
    # enabel br0
    ifconfig br0 up
    # Displays the current bridge configuration
    brctl show

    # Check the status of network card,Network cable plug status
    #ifplugd -I -i eth0 -d 0 -t 0 -r /usr/sbin/auto_bridge.sh

    # start hostapd
    hostapd /etc/hostapd.conf -B
    # set wlan new ip
    #ifconfig $wlanx 192.168.0.1
    # start udhcpd, must set $wlan static ip addr before start udhcpd
    #udhcpd /etc/udhcpd.conf 
    # get ip from dhcp server
    udhcpc -i br0 -n
fi

echo 'wifi ap shell exit'

NAT方式建立热点：

这种方式试的时候失败了，似乎是arm不支持

start NAT

sysctl net.ipv4.ip_forward=1

echo 1 > /proc/sys/net/ipv4/ip_forward

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

上面这个命令一直失败，似乎是iptables不支持

下面是一个shell脚本，以NAT方式启动热点，因为不支持，没测试过

#!/bin/sh

# Check that the /etc/udhcpd.conf file exists and can be executed
if [ ! -x /usr/sbin/hostapd ]
then
    echo "/usr/sbin/hostapd no exist or can't execute"
    exit 0
fi

# check network card wlanX
ifconfig -a|grep wlan > /dev/null
if [[ $? -ne 0 ]]
then
    echo no device wlanX
    exit 0
fi
# Gets the full name of the wlan and assigns it to wlanx
wlanx=`ifconfig -a|grep wlan|awk '{print $1}'`
if [[ $? -ne 0 ]]
then
    echo failed to get device wlanX name
    exit 0
fi

# Check that the /etc/hostapd.conf file exists and can be write
if [ ! -w /etc/hostapd.conf ]
then
    echo "/etc/hostapd.conf no exist or can't write"
    exit 0
fi

# Check that the /etc/udhcpd.conf file exists and can be write
if [ ! -w /etc/udhcpd.conf ]
then
    echo "/etc/udhcpd.conf no exist or can't write"
    exit 0
fi

# network card configure file: /etc/network/interfaces
#busybox sed -i "s/eth0/br0/g" /etc/network/interfaces
#busybox sed -i "s/auto wlan0/#auto wlan0/g" /etc/network/interfaces
#busybox sed -i "s/iface wlan0 inet dhcp/#iface wlan0 inet dhcp/g" /etc/network/interfaces

# check command
if [ "$1" != "start" -a "$1" != "stop" -a "$1" != "restart" ]
then
    echo paramter error.only accept start/stop/restart.
fi

# Close all related programs
if [ "$1" = "stop" -o "$1" = "restart" -o "$1" = "start" ]
then                                                                            
    echo "Stopping the hostapd and udhcpd and wpa_supplicant : "
    killall hostapd >/dev/null 2>&1
    killall udhcpd >/dev/null 2>&1
    killall wpa_supplicant > /dev/null 2>&1
fi

if [ "$1" = "start" -o "$1" = "restart" ]
then
    # /etc/hostapd.conf
    echo "Starting the hostapd and udhcpd : "
    wlan_old=`cat /etc/hostapd.conf|grep '^interface'`
    wlan_new="interface="$wlanx
    busybox sed -i "s/$wlan_old/$wlan_new/g" /etc/hostapd.conf

    # /etc/udhcpd.conf
    wlan_old=`cat /etc/udhcpd.conf|grep '^interface'`
    wlan_new="interface    "$wlanx"    #default: eth0"
    busybox sed -i "s/$wlan_old/$wlan_new/g" /etc/udhcpd.conf

    #start bridge eth0
    ifconfig eth0 0.0.0.0
    ifconfig $wlanx 0.0.0.0
    # Delete possible Bridges
    brctl delbr br0 >/dev/null 2>&1

    # Check the status of network card,Network cable plug status
    #ifplugd -I -i eth0 -d 0 -t 0 -r /usr/sbin/auto_bridge.sh
    ifplugd -I -i eth0 -d 0 -t 0 -r `udhcpc -i eth0 -n`

    # start hostapd
    hostapd /etc/hostapd.conf -B
    # set wlan new ip
    ifconfig $wlanx 192.168.0.1
    # start udhcpd, must set $wlan static ip addr before start udhcpd
    udhcpd /etc/udhcpd.conf 

    # start NAT
    sysctl net.ipv4.ip_forward=1
    #echo 1 > /proc/sys/net/ipv4/ip_forward
    iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
fi

echo 'wifi ap shell exit'

参考：

http://w1.fi/

http://w1.fi/cgit/hostap/plain/hostapd/hostapd.conf

http://hantianliliang.blog.sohu.com/304891332.html

http://hantianliliang.blog.sohu.com/304879882.html