picoX7

A software simulation of the Yamaha DX7 with a MIDI interface for the Raspberry Pi Pico

Slightly boring video of the picoX7 playing the Yamaha DX7 ROM cartrdige 1A patches...

Software dependencies

• https://github.com/AnotherJohnH/Platform
• arm-none-eabi-gcc
• cmake
• ninja (make works too)
• SDL2 (for native test target)

Both Pico and native targets should build on MacOS or Linux.

Hardware information

For more information on the circuit above see the schematic and the hardware blog

• Currently building for an I2S DAC based around the Cirrus Logic CS4344 from WaveShare (see below) Works well but notice Cirrus Logic have discontinued this device. Should be easy to switch to another I2S DAC
• The Pico is significantly overclocked to 191.08 MHz to support 6 voices and generate a jitter free sample rate of 49096 Hz.
• UART-0 used as a debug console (115200 baud)
• UART-1 (RX) implements the physical MIDI-IN interface
• Two PIO state machines are used to generate I2S and MCLK for the DAC module

Alternative hardware targets

Software builds for the following hardware targets...

• WAVESHARE_GPIO_LCD - The hardware described above
• WAVESHARE_I2C_LCD - Untested LCD probably not working yet
• PIMORONI_VGA_DEMO - Support for the Pimoroni Pico VGA Demo Base (!!!! untested !!!!)

NOTE: The LCD and LED displays are optional and will not block operation if not fitted

Components

NOTE No particular affiliation with PiHut but they have a nice selection and good service

Status

Incomplete but starting to work.

Done...

• I2S (via PIO) 16-bit stereo DAC interface at 49096 Hz
• Basic MIDI in support via UART
• Voice allocator
• YM21280 OPS simulation
• Basic YM21290 EGS simulation
• DX7 voice patches are starting to sound recognisble

To do, (at least)...

• Tune EGS simulation
• Pitch envelope
• LFO
• Rate and level scaling
• Mod and key sensitivity
• Maybe a logarithmic OPS implementation
• Optimise to squeeze in more voices
• Use the 2nd Arm Cortex-M0 (currently idle!)

Limitations...

• DAC implementation is quite different to the original. Suspect dynamic range is reduced
• Hitachi 6303 (~MC6803) CPU controller and firmware is not being emulated
• not using logs for sine amplitude modulation in the OPS => almost certainly not bit accurate
• 8 voices (not 16!) - Running on just one arm core at ~85% CPU usage

See the software blog and hardware blog for more detailed progress updates.

How to build

Checkout

This repo uses git sub-modules, so checkout using --recurse to clone all the dependent source...

git clone --recurse https://github.com/AnotherJohnH/picoX7.git

or

git clone --recurse ssh://git@github.com/AnotherJohnH/picoX7.git

Build

Being developed on MacOS but should build fine on Linux too.

Indirect build of all supported targets (with cmake and ninja)...

make

Build directly using cmake...

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release -DPLT_TARGET=rpipico -DCMAKE_TOOLCHAIN_FILE=Platform/MTL/rpipico/toolchain.cmake ..
make

Flashable image will be found under the build sub directory here...

.../Source/picoX7_WAVESHARE_GPIO_LCD.uf2
.../Source/picoX7_WAVESHARE_I2C_LCD.uf2
.../Source/picoX7_PIMORONI_VGA_DEMO.uf2

License

This project is licensed under the MIT License - see the LICENSE file for details

Acknowledgements

• Ken Shirriff for his very helpful series of blogs reverse engineering the YM21280
• AJXS for their annotated disassembly of the DX7 firmware ROM
• The Dexed developers for providing an easily accessible DX7 audio reference
• The raspberry-pi foundation for the innovative RP2040
• The engineers at Yamaha