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TP-Link TL-WN821N USB WiFi dongle.md

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TP-Link TL-WN821N USB WiFi dongle.md

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TP-Link TL-WN821N v 4.2 on Linux

The chipset of the dongle is

# lsusb
Bus 002 Device 008: ID 0bda:8178 Realtek Semiconductor Corp. RTL8192CU 802.11n WLAN Adapter

Enable Kernel WiFi support

Required Kernel config

[*] Networking support  --->
	[*]   Wireless  --->
		<M>   cfg80211 - wireless configuration API
		<M>   Generic IEEE 802.11 Networking Stack (mac80211)

[*] Cryptographic API  --->
	<M>   AES cipher algorithms
	<M>   AES cipher algorithms (x86_64)
	<M>   AES cipher algorithms (AES-NI)

In-kernel driver

This driver works but after a few minutes of no traffic the connection is lost. The logs show nothing, wpa_supplicant with -d option shows nothing, and ifconfig, wpa_gui ... all show that I am still connected, however if I try to load a webpage or even ping my router, nothing happends.

Required extra Kernel config

-> Device Drivers
	[*] Network device support  --->
		[*]   Wireless LAN  --->
			<M>   Realtek rtlwifi family of devices  --->
				<M>   Realtek RTL8192CU/RTL8188CU USB Wireless Network Adapter (Module name: rtl8192cu)

In kernel 4.4.0 a new experimental driver with less features but more stable has been added but I still didn't tried it:

-> Device Drivers
    [*] Network device support  --->
        [*]   Wireless LAN  --->
            <M>   RTL8723AU/RTL8188[CR]U/RTL819[12]CU (mac80211) support (RTL8XXXU Module name: rtl8xxxu)

It can coexist with the other drivers but you will need to control which module you wish to load.

Propietary driver

Required extra Kernel config

[*] Networking support  --->
	[*]   Wireless  --->
		[*]     cfg80211 wireless extensions compatibility (See footnote below!!)

The driver can be installed from an ebuild available in Maksbotan overlay

# layman -a maksbotan
# emerge -av sys-kernel/rtl8192cu-fixes

Make sure to remove the in-kernel driver brefore using this driver

# rmmod rtl8192cu rtl_usb rtl8192c_common rtlwifi

To disable power saving (fixes bug in driver)

cat /etc/modprobe.d/8192cu.conf
# rtw_power_mgnt=0 disables power saving
# rtw_enusbss=0 disables USB autosuspend
options 8192cu rtw_power_mgnt=0 rtw_enusbss=0

To load the driver

modprobe -v 8192cu

Firmware

To get red of the following message in system log:

rtl8192cu: Loading firmware rtlwifi/rtl8192cufw_TMSC.bin
rtlwifi: Loading alternative firmware rtlwifi/rtl8192cufw.bin
rtlwifi: Firmware rtlwifi/rtl8192cufw_TMSC.bin not available

Install linux-firmware with USE=savedconfig

echo 'sys-kernel/linux-firmware savedconfig' >> /etc/portage/package.use
emerge sys-kernel/linux-firmware

Then edit file /etc/portage/savedconfig/sys-kernel/linux-firmware-* and leave only this line to avoid installing unnecessary firmwares

rtlwifi/rtl8192cufw_TMSC.bin

Then reinstall the firmware

emerge sys-kernel/linux-firmware

To make the configurartion valid for all versions of linux-firmware

mv /etc/portage/savedconfig/sys-kernel/linux-firmware-* /etc/portage/savedconfig/sys-kernel/linux-firmware

Connecting to networks

Make sure the card is recognized by the kernel

# ifconfig -a
wlp0s29u1u1: flags=4098<BROADCAST,MULTICAST>  mtu 1500
	ether a1:b2:c3:a4:b5:c6  txqueuelen 1000  (Ethernet)
	RX packets 0  bytes 0 (0.0 B)
	RX errors 0  dropped 0  overruns 0  frame 0
	TX packets 0  bytes 0 (0.0 B)
	TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

To connect to WPA networks we need to instal and configure WPA supplicant

emerge wpa_supplicant

cat /etc/conf.d/wpa_supplicant
wpa_supplicant_args="-D nl80211 -i wlp0s29u1u1 -c /etc/wpa_supplicant/wpa_supplicant.conf"

cat /etc/conf.d/net
modules_wlp0s29u1u1="wpa_supplicant"
config_wlp0s29u1u1="dhcp"

Important: Do not add wpa_supplicant to any runlevel. It will be controlled by /etc/init.d/dhcpcd.

Sample /etc/wpa_supplicant/wpa_supplicant.conf file

update_config=0 # Set to "1" if you want to let any user of group "wheel" to alter this file using tools such wpa_cli or wpa_gui
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=wheel

network={
		ssid="MyWirelessNetwork"
		psk="SuperSecretPassword"
		key_mgmt=WPA-PSK
}

Note: The propietary driver does not support the nl80211 extension so the old WEXT must to be used instead. For using it, when invoking wpa_supplicant use -D wext instead of -D nl80211. It is also possible to try them both secuentialy and use the first one that is supoprted by the current driver by using -D nl80211,wext.