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Custom DIY cdrom/pendrive emulator build, Raspberry Pi

Description

My notes on building a hardware cdrom emulator for ISO images using a Raspberry Pi Zero W, python and shell scripts https://github.com/tjmnmk/gadget_cdrom and the driver code for ST7789 controller from https://files.waveshare.com/upload/b/bd/1.3inch_LCD_HAT_code.7z

Use cases:

  • a truly open-source hardware alternative to Ventoy, in light of the issues
  • Setting up a fresh install of an OS on a computer without the need to create a bootable USB
  • Running a live OS without the need to create a bootable USB
  • Restoring an OS with Live CD tools
  • Recovering a corrupted bootloader with boot-repair-disk-64bit.iso

What's the difference between my build and the pre-compiled image at https://github.com/tjmnmk/gadget_cdrom/releases ?

  • exfat instead of fat32 for the storage (support for files larger than 4GB)
  • Fully manual build on the official release of the OS to avoid any potential security risks
  • Most recent release of Raspberry Pi OS Lite
  • LCD display instead of OLED. It's not better or cheaper, it's just because I had bought the wrong part, and had to change the code to make it work. What do I do with all the real estate on the display? Add CPU load, temperature and free space indicators, of course.
  • 中文字体 (in file names also, but only when copying directly to the image mounted on the host computer)

Build pictures

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Parts list

Software

Build

  • Cut the GPIO header pins to the right length

  • Sift through the nuts and spacers left from the previous builds to find the right combination, add a heatsink if it fits

  • Assemble

  • Download https://downloads.raspberrypi.com/raspios_lite_armhf/images/raspios_lite_armhf-2024-07-04/2024-07-04-raspios-bookworm-armhf-lite.img.xz

  • Burn the image to the microsd card using Imager

    • sudo apt install rpi-imager
    • rpi-imager

  • Mount the microsd card on the host computer

  • Enable SSH

    • sudo touch /media/$USER/bootfs/ssh

  • Add user

    • echo "rpiuser:$(echo 'rpipassword' | openssl passwd -6 -stdin)" | sudo tee /media/$USER/bootfs/userconf

  • Enable modules

    • echo "dtoverlay=dwc2" | sudo tee -a /media/$USER/bootfs/config.txt
    • echo "dwc2" | sudo tee -a /media/$USER/rootfs/etc/modules

  • Unmount, put the card into the rpi, connect a USB-Ethernet adapter to the Raspberry Pi, hook up the USB-Ethernet adapter to a power source, connect the adapter with Ethernet cable to a router for Internet access

  • Boot the Raspberry Pi

  • SSH into the Raspberry Pi

  • At this point the commands are run on the Raspberry Pi

  • Enable wifi for debugging

    • sudo nano /etc/network/interfaces

      • auto wlan0
allow-hotplug wlan0
iface wlan0 inet dhcp
iface default inet dhcp

    • sudo systemctl restart systemd-networkd

      • wpa_passphrase 'tempwifi' '9eu8xdexm08rfh0w9erf9ewf09wexr' | sudo tee /etc/wpa_supplicant/wpa_supplicant-wlan0.conf

      • sudo tee -a /etc/wpa_supplicant/wpa_supplicant-wlan0.conf <<EOF
country=CN
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
ap_scan=1
EOF

      • sudo chmod 640 /etc/wpa_supplicant/wpa_supplicant-wlan0.conf

      • sudo systemctl enable [email protected]

      • sudo systemctl start [email protected]

  • Disable IPv6

    • sudo nano /etc/sysctl.conf

      • net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

    • sudo sysctl -p

  • Reconnect with wifi

  • Enable SPI and set the time zone for the SSL to work correctly

    • sudo raspi-config
      • Interface Options, SPI, Yes, Back
      • Localisation Options, Timezone, Asia, Shanghai, Finish, Reboot (or use sudo dpkg-reconfigure tzdata)

  • (optional) Replace the original repository with Chinese mirrors if in China

    • deb http://archive.raspberrypi.com/debian/ bookworm main
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
#deb-src http://archive.raspberrypi.com/debian/ bookworm main

    • sudo tee /etc/apt/sources.list.d/raspi.list <<EOF
deb https://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ bookworm main non-free contrib rpi
deb-src https://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ bookworm main non-free contrib rpi
# deb [arch=arm64] https://mirrors.tuna.tsinghua.edu.cn/raspbian/multiarch/ bookworm main
EOF

    • sudo sed -i '1s/^/#/' /etc/apt/sources.list

  • (optional) Create a larger swap file

    • sudo swapoff -a
    • sudo dd if=/dev/zero of=/swap bs=1M count=1024
    • sudo mkswap /swap
    • sudo chmod 600 /swap
    • sudo swapon /swap
    • free -m
    • echo "/swap none swap sw 0 0" | sudo tee -a /etc/fstab
    • swapon --show

  • Update the Raspberry Pi

    • sudo apt update
    • sudo apt upgrade

  • Configure locale for unicode characters support

    • sudo dpkg-reconfigure locales
      • choose en_US.UTF-8

  • Install the required packages

    • sudo apt install -y python3-psutil lm-sensors nmon screen git p7zip-full python3-rpi.gpio python3-smbus python3-spidev python3-numpy python3-pil fonts-dejavu ntfs-3g

  • Test the display

    • cd ~
    • wget https://files.waveshare.com/upload/b/bd/1.3inch_LCD_HAT_code.7z
    • 7z x 1.3inch_LCD_HAT_code.7z
    • sudo chmod 777 -R 1.3inch_LCD_HAT_code
    • cd 1.3inch_LCD_HAT_code/1.3inch_LCD_HAT_code/python
    • sudo python3 main.py

  • (do not use) Apply kernel patch for large ISOs, recompile natively and install the kernel. Takes up a day, cross-compiling might be a better idea.

    • sudo apt install bc bison flex libssl-dev make ca-certificates

    • screen

    • cd ~

    • git clone --depth=1 https://github.com/raspberrypi/linux

      • or
        • wget https://github.com/raspberrypi/linux/archive/refs/heads/rpi-6.6.y.zip
        • unzip rpi-6.6.y.zip
        • mv linux-rpi-6.6.y linux

    • cd linux

    • KERNEL=kernel

    • head Makefile -n 4

      • 
# SPDX-License-Identifier: GPL-2.0

VERSION = 6
PATCHLEVEL = 6
SUBLEVEL = 56

    • cp drivers/usb/gadget/function/storage_common.c drivers/usb/gadget/function/storage_common.c.updated

    • create a patch

      • nano drivers/usb/gadget/function/storage_common.c.updated
      • remove six lines at line 243
      • might as well create a patch while you're at it
        • diff -Naru drivers/usb/gadget/function/storage_common.c drivers/usb/gadget/function/storage_common.c.updated > 00-remove_iso_limit.patch

    • or just use the included patch for version 6.6.56

      • patch drivers/usb/gadget/function/storage_common.c 00-remove_iso_limit.patch

    • make bcmrpi_defconfig

    • make -j1 zImage modules dtbs

    • sudo make -j1 modules_install

    • sudo cp /boot/firmware/$KERNEL.img /boot/firmware/$KERNEL-backup.img

    • sudo cp arch/arm/boot/zImage /boot/firmware/$KERNEL.img

    • sudo cp arch/arm/boot/dts/broadcom/*.dtb /boot/firmware/

    • sudo cp arch/arm/boot/dts/overlays/*.dtb* /boot/firmware/overlays/

    • sudo cp arch/arm/boot/dts/overlays/README /boot/firmware/overlays/

    • sudo reboot

  • Shutdown the Pi, remove the microsd card, mount it on the host computer (/media/$USER/bootfs and /media/$USER/rootfs), apply the patch and cross-compile the kernel. Ubuntu 24.04 host for cross-compiling

    • sudo apt install bc bison flex libssl-dev make libc6-dev libncurses5-dev
    • sudo apt install crossbuild-essential-armhf
    • cd ~
    • git clone --depth=1 https://github.com/raspberrypi/linux
    • cd linux
    • KERNEL=kernel
    • make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- bcmrpi_defconfig
    • check the version head Makefile -n 4
    • apply the patch patch drivers/usb/gadget/function/storage_common.c 00-remove_iso_limit.patch
    • make -j8 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs
    • sudo env PATH=$PATH make -j8 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- INSTALL_MOD_PATH=/media/$USER/rootfs modules_install
    • sudo cp /media/$USER/bootfs/$KERNEL.img /media/$USER/bootfs/$KERNEL-backup.img
    • sudo cp arch/arm/boot/zImage /media/$USER/bootfs/$KERNEL.img
    • sudo cp arch/arm/boot/dts/broadcom/*.dtb /media/$USER/bootfs/
    • sudo cp arch/arm/boot/dts/overlays/*.dtb* /media/$USER/bootfs/overlays/
    • sudo cp arch/arm/boot/dts/overlays/README /media/$USER/bootfs/overlays/
    • sudo umount /media/$USER/bootfs
    • sudo umount /media/$USER/rootfs

  • Install the gadget_cdrom

    • cd /opt
    • sudo git clone https://github.com/placebeyondtheclouds/gadget_cdrom.git
    • sudo git clone https://github.com/placebeyondtheclouds/rpi-cdrom-emulator-build.git
    • cd gadget_cdrom
    • copy/replace the files
      • sudo cp /opt/rpi-cdrom-emulator-build/gadget_cdrom_lcd.py /opt/gadget_cdrom/
      • sudo cp /opt/rpi-cdrom-emulator-build/configST7789.py /opt/gadget_cdrom/
      • sudo cp /opt/rpi-cdrom-emulator-build/ST7789.py /opt/gadget_cdrom/
      • sudo cp /opt/rpi-cdrom-emulator-build/create_image.sh /opt/gadget_cdrom/
      • sudo cp /opt/rpi-cdrom-emulator-build/gadget_cdrom_lcd.service /opt/gadget_cdrom/gadget_cdrom_lcd.service
      • sudo wget https://archlinux.org/packages/extra/any/wqy-microhei/download/ -O /opt/gadget_cdrom/font.tgz
      • sudo tar -xvf /opt/gadget_cdrom/font.tgz -C /
    • sudo chmod +x *.py
    • sudo ./create_image.sh, 40GB, exfat
    • sudo ln -s /opt/gadget_cdrom/gadget_cdrom_lcd.service /etc/systemd/system/gadget_cdrom_lcd.service
    • sudo systemctl enable gadget_cdrom_lcd.service
    • sudo systemctl restart gadget_cdrom_lcd.service
    • sudo reboot

  • (optional) Backup

    • cd ~
    • sudo dd if=/dev/sdb | gzip -9 > cdemu-backup.img.gz
      • restore later with sudo zcat cdemu-backup.img.gz | sudo dd of=/dev/sdb if needed

  • (optional) Fast copy ISO files from the host computer to the memory card

    • sudo mkdir /mnt/iso
    • sudo mount /dev/sdb2 /media/$USER/rootfs
    • cd /media/$USER/rootfs
    • sudo mount -t exfat "$(sudo losetup -PLf iso.img --show)p1" /mnt/iso
    • sudo cp ~/Downloads/boot-repair-disk-64bit.iso /mnt/iso
    • sudo umount /mnt/iso
    • sudo umount /media/$USER/rootfs

  • (optional) Mount the image from inside the rpi

    • sudo systemctl stop gadget_cdrom_lcd.service
    • sudo umount /iso
    • sudo mount -t exfat "$(sudo losetup -PLf /iso.img --show)p1" /iso
    • sudo umount /iso

Todo

  • fix display flickering
  • fix Chinese file names

Takeaways

  • Long startup time, about a minute

References

bugfixes

DEBUG:__main__:isolist: []
DEBUG:__main__:Pressed mount
Traceback (most recent call last):
  File "/opt/gadget_cdrom/gadget_cdrom.py", line 382, in <module>
    Main().main()
  File "/opt/gadget_cdrom/gadget_cdrom.py", line 355, in main
    f()
  File "/opt/gadget_cdrom/gadget_cdrom.py", line 370, in _button_mount
    self._state.insert_iso()
  File "/opt/gadget_cdrom/gadget_cdrom.py", line 140, in insert_iso
    iso_name = self.iso_ls()[self.get_iso_select()]
               ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
IndexError: list index out of range

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CD-DVD ISO hardware emulation

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