Sitka Instruments Gravity Firmware Abstraction

This library helps make writing firmware for the Sitka Instruments Gravity eurorack module easier by abstracting away the initialization and peripheral interactions. Now your firmware code can just focus on the logic and behavior of the app, and keep the low level code neatly tucked away in this library.

The latest releases of all Sitka Instruments Gravity firmware builds can be found on the Updater page. You can use this page to flash the latest build directly to the Arduino Nano on the back of your module.

Installation

Download or git clone this repository into your Arduino > libraries folder.

Common directory locations:

• [Windows] C:\Users\{username}\Documents\Arduino\libraries
• [Mac] /Users/{username}/Documents/Arduino/libraries
• [Linux] ~/Arduino/libraries

Required Third-party Libraries

• uClock [MIT] - (Included with this repo) Handle clock tempo, external clock input, and internal clock timer handler.
• RotateEncoder [BSD] - Library for reading and interpreting encoder rotation.
• U8g2 [MIT] - Graphics helper library.
• NeoHWSerial [GPL] - Hardware serial library with attachInterrupt.

Example

Here's a trivial example showing some of the ways to interact with the library. This script rotates the active clock channel according to the set tempo. The encoder can change the temo or rotation direction. The play/pause button will toggle the clock activity on or off. The shift button will freeze the clock from advancing the channel rotation.

#include "libGravity.h"

byte idx = 0;
bool reversed = false;
bool freeze = false;
byte selected_param = 0;

// Initialize the gravity library and attach your handlers in the setup method.
void setup() {
    // Initialize Gravity.
    gravity.Init();

    // Attach handlers.
    gravity.clock.AttachIntHandler(IntClock);
    gravity.encoder.AttachRotateHandler(HandleRotate);
    gravity.encoder.AttachPressHandler(ChangeSelectedParam);
    gravity.play_button.AttachPressHandler(HandlePlayPressed);

    // Initial state.
    gravity.outputs[idx].High();
}

// The loop method must always call `gravity.Process()` to read any peripherial state changes.
void loop() {
    gravity.Process();
    freeze = gravity.shift_button.On();
    UpdateDisplay();
}

// The rest of the code is your apps logic!

void IntClock(uint32_t tick) {
    if (tick % 12 == 0  && ! freeze) {
        gravity.outputs[idx].Low();
        if (reversed) {
            idx = (idx == 0) ? OUTPUT_COUNT - 1 : idx - 1;
        } else {
            idx = (idx + 1) % OUTPUT_COUNT;
        }
        gravity.outputs[idx].High();
    }
}

void HandlePlayPressed() {
    gravity.clock.Pause();
    if (gravity.clock.IsPaused()) {
        for (int i = 0; i < OUTPUT_COUNT; i++) {
            gravity.outputs[i].Low();
        }
    }
}

void HandleRotate(int val) {
    if (selected_param == 0) {
        gravity.clock.SetTempo(gravity.clock.Tempo() + val);
    } else if (selected_param == 1) {
        reversed = (val < 0);
    }
}

void ChangeSelectedParam() {
    selected_param = (selected_param + 1) % 2;
}

void UpdateDisplay() {
    gravity.display.clearDisplay();

    if (freeze) {
        gravity.display.setCursor(42, 30);
        gravity.display.print("FREEZE!");
        gravity.display.display();
        return;
    }

    gravity.display.setCursor(10, 0);
    gravity.display.print("Tempo: ");
    gravity.display.print(gravity.clock.Tempo());

    gravity.display.setCursor(10, 10);
    gravity.display.print("Direction: ");
    gravity.display.print((reversed) ? "Backward" : "Forward");

    gravity.display.drawChar(0, selected_param * 10, 0x10, 1, 0, 1);

    gravity.display.display();
}

Builing New Firmware Using libGravity

When starting a new firmware sketch you can use the skeleton app as a place to start.

Building New Firmware from scratch

If you do not want to use the libGravity hardware abstraction library and want to roll your own vanilla firmware, take a look at the peripherials.h file for the pinout definitions used by the module.

Build for release

$ arduino-cli compile -v -b  arduino:avr:nano ./firmware/Gravity/Gravity.ino -e --output-dir=./build/