arozos/Quick Notes for Setting Up Raspberry Pi 4 as WiFi Router.md

Quick Notes for Setting Up Raspberry Pi 4 as WiFi Router

This is just a quick notes for myself on how to setup a Raspberry Pi 4 with Mercury AC650M USB WiFi Adapter

Problem

The current setup of the system make use of a ARGON ONE metal case which, will make the build in WiFi adapter really hard to use as an AP. Hence, we need to setup an external WiFi adapter for this purpose.

Required Parts

• Mercury USB WiFi Adapter AC650M (Dual baud 5G no driver version)
• ARGON ONE metal case
• Raspberry Pi 4B
• 64GB Micro SD card

Installation

1. Install Raspberry Pi OS and run apt-updates

2. Download the driver for RTL8821CU

   mkdir -p ~/build
   cd ~/build
   git clone https://github.com/brektrou/rtl8821CU.git
   

3. Install DKMS

   sudo apt-get install dkms
   

4. Upgrade apt

   sudo apt update -y
   sudo apt upgrade -y
   

5. Install bc and reboot

   sudo apt-get install bc
   sudo reboot
   

6. Edit the Make file of the downloaded repo and change these two lines as follows

   CONFIG_PLATFORM_I386_PC = y
   CONFIG_PLATFORM_ARM_RPI = n
   

to

   CONFIG_PLATFORM_I386_PC = n
   CONFIG_PLATFORM_ARM_RPI = y

1. Fix the compile flag on ARM processor

   sudo cp /lib/modules/$(uname -r)/build/arch/arm/Makefile /lib/modules/$(uname -r)/build/arch/arm/Makefile.$(date +%Y%m%d%H%M)
   sudo sed -i 's/-msoft-float//' /lib/modules/$(uname -r)/build/arch/arm/Makefile
   sudo ln -s /lib/modules/$(uname -r)/build/arch/arm /lib/modules/$(uname -r)/build/arch/armv7l
   

2. Build via DKMS

   sudo ./dkms-install.sh
   

3. Plug your USB-wifi-adapter into your PC

4. If wifi can be detected, congratulations. If not, maybe you need to switch your device usb mode by the following steps in terminal:

   1. Find your usb-wifi-adapter device ID, like "0bda:1a2b", by type: lsusb

   2. Need install usb_modeswitch

      sudo usb_modeswitch -KW -v 0bda -p 1a2b
      systemctl start bluetooth.service
      

5. Edit usb_modeswitch rules:

   udo nano /lib/udev/rules.d/40-usb_modeswitch.rules
   

6. Append before the end line LABEL="modeswitch_rules_end" the following:

   # Realtek 8211CU Wifi AC USB
   ATTR{idVendor}=="0bda", ATTR{idProduct}=="1a2b", RUN+="/usr/sbin/usb_modeswitch -K -v 0bda -p 1a2b"