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Customized Denon Prime 4 Firmware

This repository contains the efforts done to create and flash custom firmware for the Denon Prime 4. This may also be relevant to other Denon DJ equipment, however the main efforts are focused on the Denon Prime 4.

Prebuilt firmware

You can download the latest prebuilt version of the customized firmware from here directly or access the other versions via the GitHub project Releases page.

Setup

Steps below have only been tested on an Arch Linux system. Basic development packages (for example build-essentials or base-devel package), u-boot tools and 7-zip are required to be installed on your system.

Furthermore, Buildroot has its own list of requirements.

You will also need QEMU (specifically its ARM emulation) with it registered via binfmt to execute ARM binaries. On Arch Linux this would be covered by installing qemu-user-static and from AUR binfmt-qemu-static (you could also just write the config file binfmt-qemu-static installs yourself).

To reproduce the modified firmware with OpenSSH:

  1. Run ./unpack.sh to download and unpack the original firmware package.
  2. Run ./clone-buildroot.sh to download the matching buildroot environment via Git to the buildroot/2021.02.10 directory.
  3. Run ./compile-buildroot.sh to build the required toolchain and packages in buildroot. Note that this will ask for sudo access to modify the unpacked firmware images via loopback mount.
  4. Run ./pack.sh to finally pack the modified image files back into a new firmware package. It will have a .dtb extension but you can rename this to .img and flash it directly to your hardware.
  5. Optionally run ./unpack-updater.sh to download Denon's original Windows tool for flashing firmware via USB cable, then run ./generate-updater-win.sh to download 7-zip's SFX module to generate a self-extracting executable based on that tool but with your own image instead.

Customizations

  • Use ./mount.sh to chroot into unpacked rootfs at any time.
  • Use ./mount.sh --write to chroot into rootfs without read-only flags set. Do your modifications and exit the shell, and it will be stored in the rootfs.
  • You can pass any command to ./mount.sh such as (echo YourPassword123 && echo YourPassword123) | ./mount.sh --write passwd for scripting.

Information

Reboot into update mode from SSH

Command reboot loader will reboot the device into update mode. The same command is called from the original /usr/Engine/Scripts/engine script.

Buildroot

The rootfs seems to be built using Buildroot 2021.02.10 with the kernel version being 5.10.109-inmusic-2022-03-30-rt64 #1 SMP PREEMPT_RT Wed May 18 00:35:15 UTC 2022 armv7l GNU/Linux at the time of writing this.

This repository makes use of that fact to build software in an easy manner.

Firmware update source

The firmware pulls the latest firmware and its URL from https://autoupdate.airmusictech.com/PrimeUpdates.xml.

Notes

These are just my own notes and findings in the original firmware.

  • Root filesystem built with buildroot 2021.02.10 (apparently erroneously git describe'd in firmware as 2021.02.9-83-g1f864943a0), so this is what I'm using for my modifications as well
  • Incomplete list of pre-installed software on PRIME 4 firmware:
    • alsa-utils 1.2.4
    • busybox 1.33.2
    • bzip2 1.0.8
    • dfu-util 0.9
    • flac 1.3.3
    • kmod 29 +ZSTD +XZ +ZLIB +LIBCRYPTO -EXPERIMENTAL
    • lame 3.100
    • libcap 2.48
    • libexpat 1.8.4
    • libgpiod 1.6.3 with tools
    • libmali 14.0 (r1p0, without OpenCL)
    • libopenssl 1.1
    • libpng 16.37.0
    • libsamplerate 0.1.8
    • libzlib 1.2.11
    • mpg123 1.25.15
    • OpenSSL 1.1
    • pixz 1.0.7
    • Qt5 framework installed to /usr/qt and loaded via LD_LIBRARY_PATH=/usr/qt/lib
    • systemd 247 -PAM -AUDIT -SELINUX -IMA -APPARMOR -SMACK -SYSVINIT -UTMP -LIBCRYPTSETUP -GCRYPT +GNUTLS -ACL +XZ -LZ4 +ZSTD -SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 -IDN -PCRE2 default-hierarchy=hybrid
    • xz/liblzma 5.2.5
    • zstd 1.4.9
    • …?
  • Engine
    • Installed in /usr/Engine
    • Referenced to as "Planck", specifically versioned as Planck-1.2.1-3210-g1ab18eaa
    • This is probably the Denon-internal project name for Engine/Engine OS
    • Seems to be built by Jenkins and its build tag seems to be jenkins-Planck-Embedded_Release-1188
  • SoundSwitch
    • Installed in /usr/SoundSwitch
    • Referenced to simply as "SoundSwitch", specifically version with git hash 0b20b3f96a
  • Customizations seem to have the "az01" prefix attached to file names or service names
  • There is a reference to Akai MPC hardware which is the configuration's file path for the display brightness setting
  • OS uses file system overlays for /etc and /var to redirect changes to /media/az01-internal/system/
  • Credentials for streaming services are stored in /media/az01-internal/StreamingAccounts.json
    • Beatport LINK credentials specifically are just bare username and password
  • At least on my device, an old firmware version from 2022-03-05 seems to be stored in /media/az01-internal/az01-update.img for some reason
  • Engine app is its own systemd service (/etc/systemd/system/engine.service)
    • actually calls a wrapper script which does device-specific setup for performance, GPU drivers, initial device values etc.
    • Engine app itself is a Qt app called with above LD_LIBRARY_PATH hack
    • Engine app renders directly to framebuffer, no X or Wayland involved or even installed on the original firmware
    • Engine app also does the fade transition from boot logo (note the version number being displayed until Engine starts and it abruptly disappears) to the Engine UI
  • Platters, controls, sliders, etc. all provided via MIDI to the internal system. Pretty much seems to be same thing as what is done in Computer-attached mode where it's MIDI via USB.
  • Firmware update process checks the SHA-1 hashes provided for the xz-compressed images in the device tree blob. These are automatically reconstructed by my modification process.

Information below is from the original repository by @ghuntley.

denon prime4 firmware research

notes

inspecting the firmware

$ file PRIME4-2.2.1-Update.img 
PRIME4-2.2.1-Update.img: Device Tree Blob version 17, size=141671335, boot CPU=0, string block size=103, DT structure block size=141670280

The device tree blob is "compiled" by a special compiler that produces the binary in the proper form for U-Boot and Linux to understand.

$ brew install u-boot-tools
$ sudo apt-get install u-boot-tools

$ dumpimage -l PRIME4-2.2.1-Update.img          
FIT description: JC11 upgrade image
Created:         Wed May 18 07:14:06 2022
 Image 0 (splash)
  Description:  Splash screen
  Created:      Wed May 18 07:14:06 2022
  Type:         Unknown Image
  Compression:  Unknown Compression
  Data Size:    4976 Bytes = 4.86 KiB = 0.00 MiB
  Hash algo:    sha1
  Hash value:   6c80d25a71311d1b385adbd598bfe7309b716767
 Image 1 (recoverysplash)
  Description:  Update mode splash screen
  Created:      Wed May 18 07:14:06 2022
  Type:         Unknown Image
  Compression:  Unknown Compression
  Data Size:    5520 Bytes = 5.39 KiB = 0.01 MiB
  Hash algo:    sha1
  Hash value:   f2f25f8a52f4a9cbba8d89e25f45dead69aefdca
 Image 2 (rootfs)
  Description:  Root filesystem
  Created:      Wed May 18 07:14:06 2022
  Type:         Unknown Image
  Compression:  Unknown Compression
  Data Size:    141659132 Bytes = 138339.00 KiB = 135.10 MiB
  Hash algo:    sha1
  Hash value:   e845bd36f1be5368fb0d5b113f0ca68a5e949aa5

extracting the firmware

dumpimage -T flat_dt -p 0 -o splash.xz PRIME4-2.2.1-Update.img 
dumpimage -T flat_dt -p 1 -o recovery.xz PRIME4-2.2.1-Update.img
dumpimage -T flat_dt -p 2 -o rootfs.xz PRIME4-2.2.1-Update.img

sudo apt-get install xz-utils p7zip e2tools

xz -d splash.xz
xz -d recovery.xz
xz -d rootfs.xz

$ e2ls rootfs
bin          boot         dev          etc          home         lib          
lib32        linuxrc      lost+found   media        mnt          opt          
proc         root         run          sbin         srv          sys          
tmp          usr          var