Posts tagged as firmware

  • I recently released the 2.0.0 firmware for 16n, the open-source fader controller I maintain and support. This update, though substantial, is focused on one thing: improving the end-user experience around customisation. It allows users to customise the settings of their 16n using only a web browser. Not only that, but their settings will now persist between firmware updates.

    I wanted to unpick the interaction going on here - why I built it and, in particular, how it works - because I find it highly interesting and more than a little strange: tight coupling between a computer browser and a hardware device.

    To demonstrate, here’s a video where I explain the update for new users:


    16n is designed around a 32-bit microcontroller - Paul Stoffregen’s Teensy - which can be programmed for via the popular Arduino IDE. Prior to version 2.0.0, all configuration took place inside a single file that the end-user could edit. To alter how their device behaved, they had to edit some settings inside config.h, and then recompile the firmware and “flash” it onto the device.

    This is a complex demand to make of a user. And whilst the 16n was always envisaged as a DIY device, many people attracted to it who might not have been able to make their own have, entirely understandably, bought their own from other makers. As the project took off, “compile your own firmware“ was a less attractive solution - not to mention one that was harder to support.

    It had long seemed to me that the configuration of the device should be quite a straightforward task for the user; certainly not something that required recompiling the firmware to change. I’d been planning such a move for a successor device to 16n, and whilst that project was a bit stalled, the editor workflow was solid and fully working. I realised that I could backport the editor experience to the current device - and thus the foundation for 2.0.0 was laid.

    MIDI in the browser

    The browser communicates with 16n using MIDI, a relatively ancient serial protocol designed for interconnecting electronic musical instruments (on which more later). And it does this thanks to WebMIDI, a draft specification for a browser API for sending and receiving MIDI. Currently, it’s a bit patchily supported - but there’s good support inside Chrome, as well as Edge and Opera (so it’s not just a single-browser product). And it’s also viable inside Electron, making a cross-platform, standalone editor app possible.

    Before I can explain what’s going on, it’s worth quickly reviewing what MIDI is and what it supports.

    MIDI: a crash course

    MIDI - Musical Instrument Digital Interface describes several things:

    • a protocol for a serial communication format
    • an electronic spec for that serial communication
    • a set of connectors (5-pin DIN) and how they’re wired to support that.

    It is old. The first MIDI instruments were produced around 1981-1982, and their implementation still works today. It is somewhat simple, but really robust and reliable: it is used in thousands of studios, live shows and bedrooms around the world, to make electronic instruments talk to one another. The component with the most longevity is the protocol itself, which is now often transmitted over a USB connection (as opposed to the MIDI-specific DIN-connections of yore). “MIDI” has for many younger musicians just come to describe note-data (as opposed to audio-data) in electronic music programs, or what looks like a USB connection; five-pin DIN cables are a distant memory..

    The serial protocol consists of a set of messages that get sent between MIDI devices. There are relatively few messages. They fall into a few categories, the most obvious of which are:

    • timing messages, to indicate the tempo or pulse of a piece of music (a bit like a metronome), and whether instruments should be started, stopped, or reset to the beginning.
    • note data: when a note is ‘on’ or ‘off’, and if it’s on, what velocity it’s been played it (the spec is designed around keyboard instruments)
    • other non-note controls that are also relevant - whether a sustain pedal is pushed, or a pitch wheel bent, or if one of 127 “continuous controllers” - essentially, knobs or sliders - has been set to a particular value.

    16n itself transmits “continuous controllers” - CCs - from each of its sliders, for instance.

    There’s also a separate category of message called System Exclusive which describe messages that an instrument manufacturer has got their own implementation for at the device end. One of the most common uses for ‘SysEx’ data was transmitting and receiving the “patch data” of a synthesizer - all the settings to define a specific sound. SysEx could be used to backup sound programs, or transmit them to a device, and this meant musicians could keep many more sounds to hand than their instrument could store. SysEx was also used by early samplers as a slow way of transmitting sample data - you could send an audio file from a computer, slowly, down a MIDI cable. And it could be also used to enable computer-based “editors”, whereby a patch could be edited on a large screen, and then transmitted to the device as it was edited.

    Each SysEx message begins with a few bytes for a manufacturer to identify themselves (so as not to send it to any other devices on the MIDI chain), a byte to define a message number, and then a stream of data. What that data is is up to the manufacturer - and usually described somewhere in the back pages of the manual.

    Like the DX7 editors of the past, the 16n editor uses MIDI SysEx to send data to and from the hardware.

    How the 16n editor uses SysEx

    With all the background laid out, it’s perhaps easiest just to describe the flow of data in the 16n editor’s code.

    • When a user opens the editor in a web browser, the browser waits for a MIDI interface called 16n to connect. It hears about this via a callback from the WebMIDI API.
    • When it finds one, it starts polling that connection with a message meaning give me your config!
    • If 16n sees a message aimed at a 16n requesting a config, it takes its current configuration, and emits it as a stream of hex inside a SysEx message: here is my config.
    • The editor app can then stop polling, and instantiate a Configuration object from that data, which in turn will spin up the reactive Svelte UI.
    • Once a user has made some edits in the browser, they choose to transmit the config to the device: this again transmits over SysEx, saying to the device: here is a new config for you.
    • The 16n receives the config, stores it in its EEPROM, and then sets itself to use that config.
    • If a 16n interface disconnects, the WebMIDI API sends another callback, and the configuration interface dismantles itself.

    Each message in italics is a different message ID, but that’s the limit of the SysEx vocabulary for 16n: transmitting current state, receiving a new one, and being prompted to send current state.

    With all that in place, the changes to the firmware are relatively few. Firstly, it now checks if the EEPROM looks blank, at first boot, and if it is, 16n will itself store a “default” configuration into EEPROM before reading it. Then, there’s just some extra code to listen for SysEx data, process it and store it on arrival, and to transmit it when asked for.

    What this means for users

    Initially, this is a “breaking change”: at first install, a 16n will go back to a ‘default’ configuration. Except it’s then very quick to re-edit the config in a browser to what it should be, and transmit it. And from that point on, any configuration will persist between firmware upgrades. Also, users can store JSON backups of their configuration(s) on their computer, making it easy to swap between configs, or as a safeguard against user error.

    The new firwmare also makes it much easier to distribute the firmware as a binary, which is easier to install: run the loader program, drag the hex file on, and that’s that. No compilation. The source code is still available if they want it, but there’s no need to install the Arduino IDE to modify a 16n’s settings.

    As well as the settings for what MIDI channel and CC each fader transmits, the editor let users set configuration flags such as whether the LED should blink on data transmission, or how I2C should be configured. We’ve still got some bytes free to play with there, so future configuration options that should be user-settable can also be extracted like this.

    The 16n editor showing an available firmware update

    Finally, because I store the firmware version inside the firmware itself, the device can communicate this to the editor, and thus the editor can alert the user when there’s a new firmware to download, which should help everybody stay up-to-date: particularly important with a device that has such diverse users and manufacturers.

    None of this is a particular new pattern. Novation, for instance, are using this to transfer patch settings, samples, and even firmware updates to their recent synthesizers via their Components tool. It’s a very user-friendly way of approaching this task, though: it’s reliable, uses a tool that’s easy to hand, and because the browser can read configurations from the physical device, you can adjust your settings on any computer to hand, not just your own.

    I also think that by making configuration an easier task, more people will be willing to play with or explore configuration options for their device.

    The point of this post isn’t just to talk about the code and technology that makes this interaction possible, though; it’s also to look at what it feels like to use, the benefits for users, and interactions that might be possible. It’s an unusual interaction - perhaps jarring, or surprising - to configure an object by firing up a web browser and “speaking” directly to it. No wifi to set up, no hub application, no shared password. A cable between two objects, and then a tool - the browser - that usually takes to the wireless world, not the wired. WebUSB also enables similar weird, tangible interactions, in a similar way to the one I’ve performed here, but with a more flexible API.

    I think this an unusual, interesting and empowering interaction, and certainly something I’ll consider for any future connected devices: making configuration as simple and welcoming as possible, using tools a user already understands.