MiniDexed

Dexed is a FM synthesizer closely modeled on the famous DX7 by a well-known Japanese manufacturer. MiniDexed is a port to run it on a bare metal Raspberry Pi (without a Linux kernel or operating system). This is a work in progress. Contributions are highly welcome.

TODO

Contributions are highly welcome.

• Get Synth_Dexed to build with circle-stdlib
• Upload SD card contents to GitHub Releases
• Get it to build for and boot on a Raspberry Pi 4
• Get it to react to USB MIDI
• Get it to react to MIDI via Raspberry Pi 4 GPIO
• Get it to produce some sound on the headphone jack
• Get it to produce some sound produced by Dexed
• Load a default (hardcoded) sysex
• Get it to build for and boot on a Raspberry Pi 3
• Get it to build for and boot on a Raspberry Pi 2
• Get it to build for and boot on a Raspberry Pi 1
• Support multiple voices through Program Change MIDI messages
• Add functionality for loading .syx files (e.g., from Dexed_cart_1.0.zip)
• Get 8 Dexed instances to run simultaneously (like in a TX816) and mix their output together
• Add a way to configure each Dexed instance
• Allow for each Dexed instance to be stereo shifted
• Add reverb effect

I am wondering whether we can run multiple Dexed instances, in order to recreate basically an open source equivalent of the TX802 (8 DX7 instances without the keyboard in one box).

Usage

• Download from GitHub Releases
• Unzip
• Put the files into the root directory of a FAT32 formatted partition on SD/microSD card
• Put SD/microSD card into Raspberry Pi 1, 2, 3 or 4 (Zero and Zero 2 can probably be used but need HDMI or a supported i2c DAC for audio out)
• Attach headphones to the headphone jack using sounddev=sndpwm in cmdline.txt (default)
• Alternatively, attach a PCM5102A or PCM5122 based DAC and select i2c sound output using sounddev=sndi2s | sndhdmi in cmdline.txt
• Alternatively, attach a HDMI display with sound and select HDMI sound output using sounddev=sndhdmi in cmdline.txt (this may introduce slight latency)
• Attach a MIDI keyboard via USB
• Boot
• Stat playing

Building locally

E.g., to build for Raspberry Pi 4 on a Ubuntu 20.04 build system, you can use the following example. See build.yml for complete build steps that create versions for Raspberry Pi 1, 2, 3,and 4 in 32-bit and 64-bit as required.

RPI=4

git clone https://github.com/probonopd/MiniDexed
cd MiniDexed

# Recursively pull git submodules
git submodule update --init --recursive

# Install toolchain
wget -q https://developer.arm.com/-/media/Files/downloads/gnu-a/10.3-2021.07/binrel/gcc-arm-10.3-2021.07-x86_64-aarch64-none-elf.tar.xz
tar xf gcc-arm-*-*.tar.xz 
export PATH=$(readlink -f ./gcc-*/bin/):$PATH

# Build circle-stdlib library
cd circle-stdlib/
./configure -r ${RPI} --prefix "aarch64-none-elf-"
make -j$(nproc)
cd ..

# Build MiniDexed
cd src
make -j$(nproc)
ls *.img
cd ..

# Get Raspberry Pi boot files
cd ./circle-stdlib/libs/circle/boot
make
make armstub64
cd -

# Make zip that contains Raspberry Pi 4 boot files. The contents can be copied to a FAT32 formatted partition on a microSD card
mkdir -p sdcard
cp -r ./circle-stdlib/libs/circle/boot/* sdcard
mv sdcard/config64.txt sdcard/config.txt
rm -rf sdcard/config32.txt sdcard/README sdcard/Makefile sdcard/armstub sdcard/COPYING.linux
cp ./src/*img sdcard/
zip -r MiniDexed_Raspberry_Pi_${RPI}.zip sdcard/*

# Optionally, create a RPi image. This can be written to a microSD card using tools like Etcher or dd
sudo apt install --yes  mount parted
IMG="`date +%Y-%m-%d`_minidexed-RPi${RPI}.img"
dd of="${IMG}" seek=50MiB bs=1 count=0
sudo parted "${IMG}" mktable msdos
sudo parted "${IMG}" mkpart primary fat32 2048s 100%
DEV=`sudo losetup --find --partscan --show "${IMG}"`
sudo mkfs.vfat -F 32 -n BOOT "${DEV}p1"
mkdir boot
sudo mount "${DEV}p1" boot
sudo cp sdcard/* boot
sudo umount boot
sudo losetup -d "${DEV}"
rm -r boot

Acknowledgements

• asb2m10 for the Dexed sound engine
• dcoredump for https://codeberg.org/dcoredump/Synth_Dexed, a port of Dexed for embedded systems
• rsta2 for https://github.com/rsta2/circle, the library to run code on bare betal Raspberry Pi (without a Linux kernel or operating system) and for the initial MiniDexed code
• smuehlst for https://github.com/smuehlst/circle-stdlib, a version with Standard C and C++ library support