Blog:
嵌入式平台WIFI AP 模式测试

Monday, October 26, 2020

简介

本文介绍基于ARM嵌入式平台使用开源Hostapd软件配置测试WiFi Access Point模式,也就是AP模式。

本文所使用的ARM嵌入式平台来自于Toradex 基于NXP最新的iMX8 SoC(基于Cortex-A72+A53和Coretex-M4架构)的ARM计算机模块Apalis iMX8QM 4GB WB IT,模块上面集成了AzureWave AW-CM276NF WiFi/BT 模块,其具体WiFi参数如下:

Wi-fi Adapter Wi-Fi Standards Bluetooth version Adapter's Chipset Antenna Configuration
AzureWave AW-CM276NF 802.11 a/b/g/n/ac 5.0 compliant with 2.1 Marvell 88W8997 Dual-Band 802.11ac 2x2 MU-MIMO

准备

Apalis iMX8QM 4GB WB IT ARM核心版配合Ioxra 载板,连接调试串口UART1(载板X22)到开发主机方便调试。

Apalis iMX8安装Toradex Ycoto Linux Reference Multimedia image V5.0.0 2020Q3季度版本,详细信息请参考这里

WiFi模块安装标准WHF4接口天线,详情请参考这里

WiFi AP模式配置

查看WiFi模块AP模式端口uap0

root@apalis-imx8:~# ifconfig -a |grep uap
uap0      Link encap:Ethernet  HWaddr C0:E4:34:2F:C6:A1

配置Hostapd配置文件

./ file - /etc/hostapd.conf,Hostapd服务配置文件,里面预设了很多配置项目,这里只将必要的进行修改,其他可以自行根据实际需要来配置。

--- a/etc/hostapd.conf
+++ b/etc/hostapd.conf
@@ -5,7 +5,7 @@
# management frames with the Host AP driver); wlan0 with many nl80211 drivers
# Note: This attribute can be overridden by the values supplied with the '-i'
# command line parameter.
-interface=wlan0
+interface=uap0

# In case of atheros and nl80211 driver interfaces, an additional
# configuration parameter, bridge, may be used to notify hostapd if the
@@ -85,7 +85,7 @@
##### IEEE 802.11 related configuration #######################################

# SSID to be used in IEEE 802.11 management frames
-ssid=test
+ssid=ap-apalis-imx8
# Alternative formats for configuring SSID
# (double quoted string, hexdump, printf-escaped string)
#ssid2="test"

@@ -1234,7 +1234,7 @@
# authentication with external ACL for MAC addresses, and accounting
# The own IP address of the access point (used as NAS-IP-Address)
-own_ip_addr=127.0.0.1
+own_ip_addr=192.168.8.1

# NAS-Identifier string for RADIUS messages. When used, this should be unique
# to the NAS within the scope of the RADIUS server. Please note that hostapd
@@ -1464,7 +1464,7 @@
# Note that WPA3 is also configured with bit1 since it uses RSN just like WPA2.
# In other words, for WPA3, wpa=2 is used the configuration (and
# wpa_key_mgmt=SAE for WPA3-Personal instead of wpa_key_mgmt=WPA-PSK).
-#wpa=2
+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

@@ -1473,7 +1473,7 @@
# wpa_psk (dot11RSNAConfigPSKValue)
# wpa_passphrase (dot11RSNAConfigPSKPassPhrase)
#wpa_psk=0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
-#wpa_passphrase=secret passphrase
+wpa_passphrase=MyPassword1234

# Optionally, WPA PSKs can be read from a separate text file (containing list
# of (PSK,MAC address) pairs. This allows more than one PSK to be configured.

上面是配置2.4GHz频段的AP,如果需要配置5GHz频段,则需要修改下面内容

hw_mode=a
channel=40
ieee80211n=1

文件 - /etc/systemd/network/hostapd.network,用于配置AP 固定IP以及DHCP服务

[Match]
Name=<IF_NAME>
[Network]
Address=192.168.8.1/24
DHCPServer=yes

配置相关systemd启动服务

开机自动启动WiFi服务,当然Linux BSP已经包含了 /lib/systemd/system/enable-wifi.service 服务文件,只需要后面通过systemctl命令使能即可。

[Unit]
Description=Enable Wifi
BindsTo=sys-subsystem-net-devices-uap0.device
After=sys-subsystem-net-devices-uap0.device

[Service]
Type=oneshot
ExecStart=/usr/bin/connmanctl enable wifi
ExecStop=
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

修改默认的 Hostapd 服务文件,使其确定在Wifi服务以及uap0端口起来后再启动,避免出现启动失败。

--- a/lib/systemd/system/hostapd.service
+++ b/lib/systemd/system/hostapd.service
@@ -1,6 +1,7 @@
[Unit]
Description=Hostapd IEEE 802.11 AP, IEEE 802.1X/WPA/WPA2/EAP/RADIUS Authenticator
-After=network.target
+BindsTo=sys-subsystem-net-devices-uap0.device
+After=sys-subsystem-net-devices-uap0.device

[Service]
Type=forking

重载并使能上述修改的服务然后重新启动

$ systemctl --system daemon-reload
$ systemctl enable hostapd
$ systemctl enable enable-wifi.service
$ reboot

测试AP配置

重启后,通过PC WiFi网卡扫描可以找到 ap-apalis-imx8 AP设备,使用上面配置文件设定的密码连接后,ping通讯正常

  • on apalis imx8 linux

root@apalis-imx8:~# ifconfig uap0
uap0      Link encap:Ethernet  HWaddr C0:E4:34:2F:C6:A1  
        inet addr:192.168.8.1  Bcast:192.168.8.255  Mask:255.255.255.0
        inet6 addr: fe80::c2e4:34ff:fe2f:c6a1/64 Scope:Link
        UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
        RX packets:78 errors:0 dropped:0 overruns:0 frame:0
        TX packets:100 errors:39 dropped:0 overruns:0 carrier:0
        collisions:0 txqueuelen:1000 
        RX bytes:11466 (11.1 KiB)  TX bytes:5792 (5.6 KiB)

  • on Ubuntu desktop

$ ifconfig wlo1
wlo1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
      inet 192.168.8.72  netmask 255.255.255.0  broadcast 192.168.8.255
      inet6 fe80::8f97:db63:7329:9efb  prefixlen 64  scopeid 0x20<link>
      ether 3c:f0:11:6f:d0:47  txqueuelen 1000  (以太网)
      RX packets 951788  bytes 722874574 (722.8 MB)
      RX errors 0  dropped 0  overruns 0  frame 0
      TX packets 99168  bytes 16375180 (16.3 MB)
      TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

$ ping 192.168.8.1
PING 192.168.8.1 (192.168.8.1) 56(84) bytes of data.
64 bytes from 192.168.8.1: icmp_seq=1 ttl=64 time=5.82 ms
64 bytes from 192.168.8.1: icmp_seq=2 ttl=64 time=4.13 ms
64 bytes from 192.168.8.1: icmp_seq=3 ttl=64 time=4.15 ms

--- 192.168.8.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2001ms
rtt min/avg/max/mdev = 4.138/4.705/5.824/0.793 ms

网络共享功能配置

将WiFi模块Client模式端口连接到可连接互联网的WiFi网络,用于作为下面AP端口网络共享的端口

查看WiFi模块client模式端口

root@apalis-imx8:~# ifconfig |grep mlan
mlan0     Link encap:Ethernet  HWaddr C0:E4:34:2F:C4:A1

参考这里的说明,连接WiFi网络,连接后状态如下:

root@apalis-imx8:~# ifconfig mlan0      
mlan0     Link encap:Ethernet  HWaddr C0:E4:34:2F:C4:A1  
        inet addr:10.20.1.123  Bcast:10.20.1.255  Mask:255.255.255.0
        inet6 addr: fe80::c2e4:34ff:fe2f:c4a1/64 Scope:Link
        UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
        RX packets:18613 errors:0 dropped:39 overruns:0 frame:0
        TX packets:12421 errors:0 dropped:0 overruns:0 carrier:0
        collisions:0 txqueuelen:1000 
        RX bytes:20897583 (19.9 MiB)  TX bytes:1621867 (1.5 MiB)

使能Packet Forwarding

文件 - /etc/sysctl.d/30-ipforward.conf

net.ipv4.ip_forward=1
net.ipv6.conf.default.forwarding=1
net.ipv6.conf.all.forwarding=1

使能NAT

首先需要kernel包含下面驱动,直接编译到kernel或者编译成kernel modules都可以,当前测试BSP是已经编译为kernel modules,如果没有包含则需要重新编译kernel添加进入

root@apalis-imx8:~# zcat /proc/config.gz |grep CONFIG_IP_NF_IPTABLES                                     
CONFIG_IP_NF_IPTABLES=m
root@apalis-imx8:~# zcat /proc/config.gz |grep CONFIG_NETFILTER_XT_MATCH_CONNTRACK
CONFIG_NETFILTER_XT_MATCH_CONNTRACK=m

使用iptables使能NAT,首先创建下面iptables 规则

iptables -t nat -A POSTROUTING -o mlan0 -j MASQUERADE
iptables -A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i uap0 -o mlan0 -j ACCEPT

将上面设置的规则保存到配置文件

$ iptables-save > /etc/iptables/iptables.rules

使能iptable服务,当前BSP已经包含服务文件 /lib/systemd/system/iptables.service

$ systemctl enable iptables

重启后上述配置生效,然后启动后可以通过systemctl查看相关服务是否都启动正常

$ systemctl status hostapd
$ systemctl status enable-wifi
$ systemctl status iptables

同样使用Ubuntu desktop连接ap-apalis-imx8 AP后,如下测试可以正常连接互联网了,证明网络共享配置成功

$ ifconfig wlo1
wlo1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
      inet 192.168.8.72  netmask 255.255.255.0  broadcast 192.168.8.255
      inet6 fe80::8f97:db63:7329:9efb  prefixlen 64  scopeid 0x20<link>
      ether 3c:f0:11:6f:d0:47  txqueuelen 1000  (以太网)
      RX packets 967881  bytes 745946717 (745.9 MB)
      RX errors 0  dropped 0  overruns 0  frame 0
      TX packets 103940  bytes 17087302 (17.0 MB)
      TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

# ping 百度网址,因为AP默认没有设定DNS配置,因此连接后需要手动指定一个有效的DNS地址才能进行DNS解析

$ ping www.baidu.com
PING www.a.shifen.com (180.101.49.11) 56(84) bytes of data.
64 bytes from 180.101.49.11 (180.101.49.11): icmp_seq=1 ttl=51 time=8.97 ms
64 bytes from 180.101.49.11 (180.101.49.11): icmp_seq=2 ttl=51 time=11.2 ms
64 bytes from 180.101.49.11 (180.101.49.11): icmp_seq=3 ttl=51 time=10.8 ms
--- www.a.shifen.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 8.972/10.369/11.276/1.005 ms

总结

本文在iMX8嵌入式平台下使用Linux开源工具测试了WiFi 模块AP模式以及网络共享功能。

参考文档

https://developer.toradex.cn/knowledge-base/wi-fi-access-point-mode
https://wiki.archlinux.org/index.php/Internet_sharing

Author: 秦海,技术销售工程师,韬睿(上海)
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