A micropython module implementing the moddevices control chain protocol (currently on an STM32 development board), as well as a simple program that provides a footswitch implementation with four foot swtiches and corresponding indicator lights.
The code is currently fully-functional. It handshakes and will show up in the Mod Duo(X) UI, and you can freely assign any toggle or option signal to any of the four switch inputs. Indication of the state of the four assignments is provided via four LED output signals.
Tap tempo is under development and will be verified when this is available in the Mod Duo X (or Dwarf) firmware.
Since moving to asyncio there is an issue when assigning lists of parameters to a footswitch. It appears that the serial bytes are not consumed fast enough and the assignment fails. This is being looked into.
Currently this project runs on an ST Microelectronics NUCLEO-F446RE development board with a moddevices Arduino shield attached.
If you want to use the exact same development board, you can use the provided firmware images (compiled with the latest master branch of micropython as of December 25th, 2020) for the micropython runtime. If you want to use a different board, you can compile micropython yourself (see [required-micropython-configuration]).
If you are using an ST-Micro development board with a connected ST-LINK you will need the following drivers/utilities (assuming Windows development, using WSL for Linux when needed) to flash the firmware :
https://www.st.com/en/development-tools/stsw-link009.html
NOTE: We're using an older version since the latest fails due to a bug
https://github.com/stlink-org/stlink/releases/tag/v1.3.0
If you plan on building micropython yourself from scratch, you will need micropython as well as the ARM toolchain.
A stock build of micropython will work with no changes to the default options. Threading is no longer required now that the code has been ported to use asyncio.
This code requires one high-speed timer and is configured to use TIM2 (which is normally used for a servo on the stm32 port of micropython but we have no servos :) ).
In order to allow easy programming and debugging it is recommended that UART2 be left as the REPL uart and UART6 be selected as the communication link to the Mod Duo(X). This means a small hardware modification is also required (see below).
The entire system can be powered from the Mod Duo(X). To configure this, simply change the PWR jumper to be on the E5V side. It is safe to plug the USB cable into the development board for programming and debugging while the Mod Duo(X) is powering the system (and communicating), but there is one small caveat. You must power the board from the ethernet jack (from the Mod Duo(X)) before plugging in the USB cable to the development board. If you plug the USB cable in first, the system will not power up correctly and just won't work.
Since we are using UART6 for communications to the Mod Duo(X), we need to make a small change to the Arduino shield and connect a jumper wire to make things work. This is because:
- The Arduino shield is configured to use
UART2(which is shared with the USB connection to the PC) - One pin from
UART6is not actually on the Arduino headers but is available on another header on the development board
You don't have to do this, but if you instead use UART6 for the debug/programming connection you need to remove the shield and change the powering scheme every time you make a change - which is a total pain in the ass. So, to make it work (and it is totally worth it for ease of debugging/programming), you need to do the following:
- Do not install header pins in the
TXabdRXArduino header positions on the Arduino shield. This avoids connecting the serial pins interfacing with the Mod Duo(X) withUART2on the development board (which we'll be using for debugging and flashing instead). - Install a jumper between pin
-9and pinRXon the Arduino shield - Install a jumper from pin
4ofCN10on the development board to pinTXon the Arduino shield
This effectively jumpers the UART6 pins over to the RX and TX signals going to the Mod Duo(X).
There are two steps to flashing the firmware:
If using an ST Microelectronics NUCLEO-F446RE development board, you can use the provided images for the micropython runtime. If you have compiled micropython from scratch, follow the micropython directions for your board to flash the micropython runtime onto your device.
There is a script in the root folder that uses a locally-installed st-flash.exe utility to flash the micropython firmware onto the device (assumes the ST-LINK driver is installed and the board is plugged in).
Your user-program is written in pure micropython and is flashed separately from the micropython runtime. This is done with a simple serial connection to the micropython REPL using a utility called rshell. This must be installed and there are a couple of scripts provided to flash the user program onto the device. flash_all_py.bat will flash all of the firmware (control chain protocol module and other helper modules) to the device as well as the main user program (footswitch.py). This only needs to be done once (or whenever a helper module changes). The other script - flash_footswitch_py.bat - flashes the main user program to the device. Typically this all you need to flash on a regular basis during development.
Once everything has been flashed, you can plug your "footswitch" into your Mod Duo(X) and you should see it detected in the Mod web GUI!
It is recommended you edit footswitch.py to customize the name and URL of the device as well as any DIO pin names such that they correspond to your specific board/device.