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...
- 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.
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 8 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
| Pin | Peripheral | Allocation |
|---|---|---|
| 1 | UART-0 | Debug console out (UART) TX |
| 2 | UART-0 | Debug console in (UART) RX |
| 3 | GND | UART GND |
| 6 | UART-1 | MIDI IN |
| 19 | I2C1 | SDA (for I2C LCD) |
| 20 | I2C1 | SCL (for I2C LCD) |
| 29 | PIO | I2S DATA |
| 31 | PIO | MCLK (for I2S DAC chip) |
| 32 | PIO | I2S LR CLK |
| 34 | PIO | I2S DATA CLK |
Software builds for the following hardware targets...
- WAVESHARE_GPIO_LCD - The hardware described above
- WAVESHARE_I2C_LCD - Use an I2C LCD on pins 19+20 instead of the 8-bit parallel interface
- 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
| Name | Description | Source |
|---|---|---|
| Raspberry Pi Pico | DIP module hosting an RP2040 MCU and 2 MiB Flash | PiHut |
| Waveshare Pico Audio | I2S DAC module that directly mounts under the Pico | PiHut |
| MIDI controller | Music keyboard with actual MIDI out (MIDI over the USB connector also works) | Old Roland PC-200 works for me |
| MIDI-in adapter | An optically isolated 5-pin DIN to UART interface | 3 resistors, a diode and an op-amp work well if the controller is battery powered ;-) |
| Reset button | Reset the Pico and allow Flashing | Why not included on the Pico module ?!@# |
| 16x2 I2C LCD | Optional voice name display | PiHut |
| Raspberry Pi Debug probe | Not essential but very helpful | PiHut |
NOTE No particular affiliation with PiHut but they have a nice selection and excellent service
Incomplete but starting to work.
Done...
- I2S (via PIO) 16-bit stereo DAC interface at 49096 Hz
- Basic MIDI in support via UART and USB
- Voice allocator
- YM21280 OPS simulation
- Basic YM21290 EGS simulation
- DX7 voice patches are starting to sound recognisble
- Use the 2nd Arm Cortex-M0
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
- Support for the RP2350 in the Pico-2
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 two arm cores at ~85% CPU usage
See the software blog and hardware blog for more detailed progress updates.
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
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 ..
cmake -DCMAKE_BUILD_TYPE=Release -DPLT_TARGET=native ..
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
This project is licensed under the MIT License - see the LICENSE file for details
- 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
