From 38527f9a3b39f6ec914da22fecc7bf949e979750 Mon Sep 17 00:00:00 2001
From: Rodolphe Belouin <rodolphe.belouin@gmail.com>
Date: Sun, 8 Nov 2020 04:35:14 +0100
Subject: [PATCH] Add step sequencer feature (#9703)

* sequencer: create togglable feature

* sequencer: add support for steps

* sequencer: add support for tempo and resolutions

* sequencer: schedule a message print at the right frequency

* sequencer: send a hardcoded note

* sequencer: add support for 8 tracks

* sequencer: play several notes simultaneously

* sequencer: only play the active tracks for a given step

* sequencer: change the default behavior of the track toggler

* sequencer: make number of tracks and track notes customizable

* sequencer: move the keycodes down

Not adding them at the end of the list apparently risks breaking
compatibility with VIA.

Source: https://github.com/qmk/qmk_firmware/pull/9703#discussion_r459202733

* sequencer: add unit tests

* sequencer: add unit test for matrix_scan_sequencer

* sequencer: expose internal state for better unit-testability

* sequencer: add unit tests for matrix_scan_sequencer
---
 build_test.mk                               |   1 +
 common.mk                                   |   1 +
 common_features.mk                          |   7 +
 docs/_summary.md                            |   1 +
 docs/feature_sequencer.md                   |  88 +++
 quantum/process_keycode/process_sequencer.c |  62 ++
 quantum/process_keycode/process_sequencer.h |  21 +
 quantum/quantum.c                           |   7 +
 quantum/quantum.h                           |   5 +
 quantum/quantum_keycodes.h                  |  35 ++
 quantum/sequencer/sequencer.c               | 275 +++++++++
 quantum/sequencer/sequencer.h               | 122 ++++
 quantum/sequencer/tests/midi_mock.c         |  26 +
 quantum/sequencer/tests/midi_mock.h         |  26 +
 quantum/sequencer/tests/rules.mk            |  11 +
 quantum/sequencer/tests/sequencer_tests.cpp | 590 ++++++++++++++++++++
 quantum/sequencer/tests/testlist.mk         |   1 +
 testlist.mk                                 |   1 +
 18 files changed, 1280 insertions(+)
 create mode 100644 docs/feature_sequencer.md
 create mode 100644 quantum/process_keycode/process_sequencer.c
 create mode 100644 quantum/process_keycode/process_sequencer.h
 create mode 100644 quantum/sequencer/sequencer.c
 create mode 100644 quantum/sequencer/sequencer.h
 create mode 100644 quantum/sequencer/tests/midi_mock.c
 create mode 100644 quantum/sequencer/tests/midi_mock.h
 create mode 100644 quantum/sequencer/tests/rules.mk
 create mode 100644 quantum/sequencer/tests/sequencer_tests.cpp
 create mode 100644 quantum/sequencer/tests/testlist.mk

diff --git a/build_test.mk b/build_test.mk
index d13d9a515b..e705c6a3ba 100644
--- a/build_test.mk
+++ b/build_test.mk
@@ -49,6 +49,7 @@ endif
 
 include common_features.mk
 include $(TMK_PATH)/common.mk
+include $(QUANTUM_PATH)/sequencer/tests/rules.mk
 include $(QUANTUM_PATH)/serial_link/tests/rules.mk
 ifneq ($(filter $(FULL_TESTS),$(TEST)),)
 include build_full_test.mk
diff --git a/common.mk b/common.mk
index aea29a7a20..c13b5e2768 100644
--- a/common.mk
+++ b/common.mk
@@ -21,4 +21,5 @@ COMMON_VPATH += $(QUANTUM_PATH)/keymap_extras
 COMMON_VPATH += $(QUANTUM_PATH)/audio
 COMMON_VPATH += $(QUANTUM_PATH)/process_keycode
 COMMON_VPATH += $(QUANTUM_PATH)/api
+COMMON_VPATH += $(QUANTUM_PATH)/sequencer
 COMMON_VPATH += $(DRIVER_PATH)
diff --git a/common_features.mk b/common_features.mk
index 32028c8af5..b49c08c50b 100644
--- a/common_features.mk
+++ b/common_features.mk
@@ -38,6 +38,13 @@ ifeq ($(strip $(AUDIO_ENABLE)), yes)
     SRC += $(QUANTUM_DIR)/audio/luts.c
 endif
 
+ifeq ($(strip $(SEQUENCER_ENABLE)), yes)
+    OPT_DEFS += -DSEQUENCER_ENABLE
+    MUSIC_ENABLE = yes
+    SRC += $(QUANTUM_DIR)/sequencer/sequencer.c
+    SRC += $(QUANTUM_DIR)/process_keycode/process_sequencer.c
+endif
+
 ifeq ($(strip $(MIDI_ENABLE)), yes)
     OPT_DEFS += -DMIDI_ENABLE
     MUSIC_ENABLE = yes
diff --git a/docs/_summary.md b/docs/_summary.md
index 2e874fb1cd..864fdee0db 100644
--- a/docs/_summary.md
+++ b/docs/_summary.md
@@ -80,6 +80,7 @@
     * [One Shot Keys](one_shot_keys.md)
     * [Pointing Device](feature_pointing_device.md)
     * [Raw HID](feature_rawhid.md)
+    * [Sequencer](feature_sequencer.md)
     * [Swap Hands](feature_swap_hands.md)
     * [Tap Dance](feature_tap_dance.md)
     * [Tap-Hold Configuration](tap_hold.md)
diff --git a/docs/feature_sequencer.md b/docs/feature_sequencer.md
new file mode 100644
index 0000000000..8c8587a9b8
--- /dev/null
+++ b/docs/feature_sequencer.md
@@ -0,0 +1,88 @@
+# Sequencer
+
+Since QMK has experimental support for MIDI, you can now turn your keyboard into a [step sequencer](https://en.wikipedia.org/wiki/Music_sequencer#Step_sequencers)!
+
+!> **IMPORTANT:** This feature is highly experimental, it has only been tested on a Planck EZ so far. Also, the scope will be limited to support the drum machine use-case to start with.
+
+## Enable the step sequencer
+
+Add the following line to your `rules.mk`:
+
+```make
+SEQUENCER_ENABLE = yes
+```
+
+By default the sequencer has 16 steps, but you can override this setting in your `config.h`:
+
+```c
+#define SEQUENCER_STEPS 32
+```
+
+## Tracks
+
+You can program up to 8 independent tracks with the step sequencer. Select the tracks you want to edit, enable or disable some steps, and start the sequence!
+
+## Resolutions
+
+While the tempo defines the absolute speed at which the sequencer goes through the steps, the resolution defines the granularity of these steps (from coarser to finer).
+
+|Resolution   |Description            |
+|----------   |-----------            |
+|`SQ_RES_2`   |Every other beat       |
+|`SQ_RES_2T`  |Every 1.5 beats        |
+|`SQ_RES_4`   |Every beat             |
+|`SQ_RES_4T`  |Three times per 2 beats|
+|`SQ_RES_8`   |Twice per beat         |
+|`SQ_RES_8T`  |Three times per beat   |
+|`SQ_RES_16`  |Four times per beat    |
+|`SQ_RES_16T` |Six times per beat     |
+|`SQ_RES_32`  |Eight times per beat   |
+
+## Keycodes
+
+|Keycode  |Description                                        |
+|-------  |-----------                                        |
+|`SQ_ON`  |Start the step sequencer                           |
+|`SQ_OFF` |Stop the step sequencer                            |
+|`SQ_TOG` |Toggle the step sequencer playback                 |
+|`SQ_SALL`|Enable all the steps                               |
+|`SQ_SCLR`|Disable all the steps                              |
+|`SQ_S(n)`|Toggle the step `n`                                |
+|`SQ_TMPD`|Decrease the tempo                                 |
+|`SQ_TMPU`|Increase the tempo                                 |
+|`SQ_R(n)`|Set the resolution to n                            |
+|`SQ_RESD`|Change to the slower resolution                    |
+|`SQ_RESU`|Change to the faster resolution                    |
+|`SQ_T(n)`|Set `n` as the only active track or deactivate all |
+
+## Functions
+
+|Function                                                             |Description                                            |
+|--------                                                             |-----------                                            |
+|`bool is_sequencer_on(void);`                                        |Return whether the sequencer is playing                |
+|`void sequencer_toggle(void);`                                       |Toggle the step sequencer playback                     |
+|`void sequencer_on(void);`                                           |Start the step sequencer                               |
+|`void sequencer_off(void);`                                          |Stop the step sequencer                                |
+|`bool is_sequencer_step_on(uint8_t step);`                           |Return whether the step is currently enabled           |
+|`void sequencer_set_step(uint8_t step, bool value);`                 |Enable or disable the step                             |
+|`void sequencer_set_step_on();`                                      |Enable the step                                        |
+|`void sequencer_set_step_off();`                                     |Disable the step                                       |
+|`void sequencer_toggle_step(uint8_t step);`                          |Toggle the step                                        |
+|`void sequencer_set_all_steps(bool value);`                          |Enable or disable all the steps                        |
+|`void sequencer_set_all_steps_on();`                                 |Enable all the steps                                   |
+|`void sequencer_set_all_steps_off();`                                |Disable all the steps                                  |
+|`uint8_t sequencer_get_tempo(void);`                                 |Return the current tempo                               |
+|`void sequencer_set_tempo(uint8_t tempo);`                           |Set the tempo to `tempo` (between 1 and 255)           |
+|`void sequencer_increase_tempo(void);`                               |Increase the tempo                                     |
+|`void sequencer_decrease_tempo(void);`                               |Decrease the tempo                                     |
+|`sequencer_resolution_t sequencer_get_resolution(void);`             |Return the current resolution                          |
+|`void sequencer_set_resolution(sequencer_resolution_t resolution);`  |Set the resolution to `resolution`                     |
+|`void sequencer_increase_resolution(void);`                          |Change to the faster resolution                        |
+|`void sequencer_decrease_resolution(void);`                          |Change to the slower resolution                        |
+|`bool is_sequencer_track_active(uint8_t track);`                     |Return whether the track is active                     |
+|`void sequencer_set_track_activation(uint8_t track, bool value);`    |Activate or deactivate the `track`                     |
+|`void sequencer_toggle_track_activation(uint8_t track);`             |Toggle the `track`                                     |
+|`void sequencer_activate_track(uint8_t track);`                      |Activate the `track`                                   |
+|`void sequencer_deactivate_track(uint8_t track);`                    |Deactivate the `track`                                 |
+|`void sequencer_toggle_single_active_track(uint8_t track);`          |Set `track` as the only active track or deactivate all |
+
diff --git a/quantum/process_keycode/process_sequencer.c b/quantum/process_keycode/process_sequencer.c
new file mode 100644
index 0000000000..334b4c0092
--- /dev/null
+++ b/quantum/process_keycode/process_sequencer.c
@@ -0,0 +1,62 @@
+/* Copyright 2020 Rodolphe Belouin
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "process_sequencer.h"
+
+bool process_sequencer(uint16_t keycode, keyrecord_t *record) {
+    if (record->event.pressed) {
+        switch (keycode) {
+            case SQ_ON:
+                sequencer_on();
+                return false;
+            case SQ_OFF:
+                sequencer_off();
+                return false;
+            case SQ_TOG:
+                sequencer_toggle();
+                return false;
+            case SQ_TMPD:
+                sequencer_decrease_tempo();
+                return false;
+            case SQ_TMPU:
+                sequencer_increase_tempo();
+                return false;
+            case SEQUENCER_RESOLUTION_MIN ... SEQUENCER_RESOLUTION_MAX:
+                sequencer_set_resolution(keycode - SEQUENCER_RESOLUTION_MIN);
+                return false;
+            case SQ_RESD:
+                sequencer_decrease_resolution();
+                return false;
+            case SQ_RESU:
+                sequencer_increase_resolution();
+                return false;
+            case SQ_SALL:
+                sequencer_set_all_steps_on();
+                return false;
+            case SQ_SCLR:
+                sequencer_set_all_steps_off();
+                return false;
+            case SEQUENCER_STEP_MIN ... SEQUENCER_STEP_MAX:
+                sequencer_toggle_step(keycode - SEQUENCER_STEP_MIN);
+                return false;
+            case SEQUENCER_TRACK_MIN ... SEQUENCER_TRACK_MAX:
+                sequencer_toggle_single_active_track(keycode - SEQUENCER_TRACK_MIN);
+                return false;
+        }
+    }
+
+    return true;
+}
diff --git a/quantum/process_keycode/process_sequencer.h b/quantum/process_keycode/process_sequencer.h
new file mode 100644
index 0000000000..2b85f24299
--- /dev/null
+++ b/quantum/process_keycode/process_sequencer.h
@@ -0,0 +1,21 @@
+/* Copyright 2020 Rodolphe Belouin
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "quantum.h"
+
+bool process_sequencer(uint16_t keycode, keyrecord_t *record);
diff --git a/quantum/quantum.c b/quantum/quantum.c
index dab6c9172f..ebe80ca1ea 100644
--- a/quantum/quantum.c
+++ b/quantum/quantum.c
@@ -229,6 +229,9 @@ bool process_record_quantum(keyrecord_t *record) {
             process_record_via(keycode, record) &&
 #endif
             process_record_kb(keycode, record) &&
+#if defined(SEQUENCER_ENABLE)
+            process_sequencer(keycode, record) &&
+#endif
 #if defined(MIDI_ENABLE) && defined(MIDI_ADVANCED)
             process_midi(keycode, record) &&
 #endif
@@ -633,6 +636,10 @@ void matrix_scan_quantum() {
     matrix_scan_music();
 #endif
 
+#ifdef SEQUENCER_ENABLE
+    matrix_scan_sequencer();
+#endif
+
 #ifdef TAP_DANCE_ENABLE
     matrix_scan_tap_dance();
 #endif
diff --git a/quantum/quantum.h b/quantum/quantum.h
index 42e8c00091..e63711fc31 100644
--- a/quantum/quantum.h
+++ b/quantum/quantum.h
@@ -68,6 +68,11 @@ extern layer_state_t default_layer_state;
 extern layer_state_t layer_state;
 #endif
 
+#if defined(SEQUENCER_ENABLE)
+#    include "sequencer.h"
+#    include "process_sequencer.h"
+#endif
+
 #if defined(MIDI_ENABLE) && defined(MIDI_ADVANCED)
 #    include "process_midi.h"
 #endif
diff --git a/quantum/quantum_keycodes.h b/quantum/quantum_keycodes.h
index c1e31fc867..a2cc7b38d9 100644
--- a/quantum/quantum_keycodes.h
+++ b/quantum/quantum_keycodes.h
@@ -16,6 +16,10 @@
 #ifndef QUANTUM_KEYCODES_H
 #define QUANTUM_KEYCODES_H
 
+#if defined(SEQUENCER_ENABLE)
+#    include "sequencer.h"
+#endif
+
 #ifndef MIDI_ENABLE_STRICT
 #    define MIDI_ENABLE_STRICT 0
 #endif
@@ -550,6 +554,37 @@ enum quantum_keycodes {
     JS_BUTTON31,
     JS_BUTTON_MAX = JS_BUTTON31,
 
+#if defined(SEQUENCER_ENABLE)
+    SQ_ON,
+    SQ_OFF,
+    SQ_TOG,
+
+    SQ_TMPD,  // Decrease tempo
+    SQ_TMPU,  // Increase tempo
+
+    SEQUENCER_RESOLUTION_MIN,
+    SEQUENCER_RESOLUTION_MAX = SEQUENCER_RESOLUTION_MIN + SEQUENCER_RESOLUTIONS,
+    SQ_RESD,  // Decrease resolution
+    SQ_RESU,  // Increase resolution
+
+    SQ_SALL,  // All steps on
+    SQ_SCLR,  // All steps off
+    SEQUENCER_STEP_MIN,
+    SEQUENCER_STEP_MAX = SEQUENCER_STEP_MIN + SEQUENCER_STEPS,
+
+    SEQUENCER_TRACK_MIN,
+    SEQUENCER_TRACK_MAX = SEQUENCER_TRACK_MIN + SEQUENCER_TRACKS,
+
+/**
+ * Helpers to assign a keycode to a step, a resolution, or a track.
+ * Falls back to NOOP if n is out of range.
+ */
+#    define SQ_S(n) (n < SEQUENCER_STEPS ? SEQUENCER_STEP_MIN + n : XXXXXXX)
+#    define SQ_R(n) (n < SEQUENCER_RESOLUTIONS ? SEQUENCER_RESOLUTION_MIN + n : XXXXXXX)
+#    define SQ_T(n) (n < SEQUENCER_TRACKS ? SEQUENCER_TRACK_MIN + n : XXXXXXX)
+
+#endif
+
     // always leave at the end
     SAFE_RANGE
 };
diff --git a/quantum/sequencer/sequencer.c b/quantum/sequencer/sequencer.c
new file mode 100644
index 0000000000..0eaf3a17aa
--- /dev/null
+++ b/quantum/sequencer/sequencer.c
@@ -0,0 +1,275 @@
+/* Copyright 2020 Rodolphe Belouin
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "sequencer.h"
+
+#ifdef MIDI_ENABLE
+#    include "process_midi.h"
+#endif
+
+#ifdef MIDI_MOCKED
+#    include "tests/midi_mock.h"
+#endif
+
+sequencer_config_t sequencer_config = {
+    false,     // enabled
+    {false},   // steps
+    {0},       // track notes
+    60,        // tempo
+    SQ_RES_4,  // resolution
+};
+
+sequencer_state_t sequencer_internal_state = {0, 0, 0, 0, SEQUENCER_PHASE_ATTACK};
+
+bool is_sequencer_on(void) { return sequencer_config.enabled; }
+
+void sequencer_on(void) {
+    dprintln("sequencer on");
+    sequencer_config.enabled               = true;
+    sequencer_internal_state.current_track = 0;
+    sequencer_internal_state.current_step  = 0;
+    sequencer_internal_state.timer         = timer_read();
+    sequencer_internal_state.phase         = SEQUENCER_PHASE_ATTACK;
+}
+
+void sequencer_off(void) {
+    dprintln("sequencer off");
+    sequencer_config.enabled              = false;
+    sequencer_internal_state.current_step = 0;
+}
+
+void sequencer_toggle(void) {
+    if (is_sequencer_on()) {
+        sequencer_off();
+    } else {
+        sequencer_on();
+    }
+}
+
+void sequencer_set_track_notes(const uint16_t track_notes[SEQUENCER_TRACKS]) {
+    for (uint8_t i = 0; i < SEQUENCER_TRACKS; i++) {
+        sequencer_config.track_notes[i] = track_notes[i];
+    }
+}
+
+bool is_sequencer_track_active(uint8_t track) { return (sequencer_internal_state.active_tracks >> track) & true; }
+
+void sequencer_set_track_activation(uint8_t track, bool value) {
+    if (value) {
+        sequencer_internal_state.active_tracks |= (1 << track);
+    } else {
+        sequencer_internal_state.active_tracks &= ~(1 << track);
+    }
+    dprintf("sequencer: track %d is %s\n", track, value ? "active" : "inactive");
+}
+
+void sequencer_toggle_track_activation(uint8_t track) { sequencer_set_track_activation(track, !is_sequencer_track_active(track)); }
+
+void sequencer_toggle_single_active_track(uint8_t track) {
+    if (is_sequencer_track_active(track)) {
+        sequencer_internal_state.active_tracks = 0;
+    } else {
+        sequencer_internal_state.active_tracks = 1 << track;
+    }
+}
+
+bool is_sequencer_step_on(uint8_t step) { return step < SEQUENCER_STEPS && (sequencer_config.steps[step] & sequencer_internal_state.active_tracks) > 0; }
+
+bool is_sequencer_step_on_for_track(uint8_t step, uint8_t track) { return step < SEQUENCER_STEPS && (sequencer_config.steps[step] >> track) & true; }
+
+void sequencer_set_step(uint8_t step, bool value) {
+    if (step < SEQUENCER_STEPS) {
+        if (value) {
+            sequencer_config.steps[step] |= sequencer_internal_state.active_tracks;
+        } else {
+            sequencer_config.steps[step] &= ~sequencer_internal_state.active_tracks;
+        }
+        dprintf("sequencer: step %d is %s\n", step, value ? "on" : "off");
+    } else {
+        dprintf("sequencer: step %d is out of range\n", step);
+    }
+}
+
+void sequencer_toggle_step(uint8_t step) {
+    if (is_sequencer_step_on(step)) {
+        sequencer_set_step_off(step);
+    } else {
+        sequencer_set_step_on(step);
+    }
+}
+
+void sequencer_set_all_steps(bool value) {
+    for (uint8_t step = 0; step < SEQUENCER_STEPS; step++) {
+        if (value) {
+            sequencer_config.steps[step] |= sequencer_internal_state.active_tracks;
+        } else {
+            sequencer_config.steps[step] &= ~sequencer_internal_state.active_tracks;
+        }
+    }
+    dprintf("sequencer: all steps are %s\n", value ? "on" : "off");
+}
+
+uint8_t sequencer_get_tempo(void) { return sequencer_config.tempo; }
+
+void sequencer_set_tempo(uint8_t tempo) {
+    if (tempo > 0) {
+        sequencer_config.tempo = tempo;
+        dprintf("sequencer: tempo set to %d bpm\n", tempo);
+    } else {
+        dprintln("sequencer: cannot set tempo to 0");
+    }
+}
+
+void sequencer_increase_tempo(void) {
+    // Handling potential uint8_t overflow
+    if (sequencer_config.tempo < UINT8_MAX) {
+        sequencer_set_tempo(sequencer_config.tempo + 1);
+    } else {
+        dprintf("sequencer: cannot set tempo above %d\n", UINT8_MAX);
+    }
+}
+
+void sequencer_decrease_tempo(void) { sequencer_set_tempo(sequencer_config.tempo - 1); }
+
+sequencer_resolution_t sequencer_get_resolution(void) { return sequencer_config.resolution; }
+
+void sequencer_set_resolution(sequencer_resolution_t resolution) {
+    if (resolution >= 0 && resolution < SEQUENCER_RESOLUTIONS) {
+        sequencer_config.resolution = resolution;
+        dprintf("sequencer: resolution set to %d\n", resolution);
+    } else {
+        dprintf("sequencer: resolution %d is out of range\n", resolution);
+    }
+}
+
+void sequencer_increase_resolution(void) { sequencer_set_resolution(sequencer_config.resolution + 1); }
+
+void sequencer_decrease_resolution(void) { sequencer_set_resolution(sequencer_config.resolution - 1); }
+
+uint8_t sequencer_get_current_step(void) { return sequencer_internal_state.current_step; }
+
+void sequencer_phase_attack(void) {
+    dprintf("sequencer: step %d\n", sequencer_internal_state.current_step);
+    dprintf("sequencer: time %d\n", timer_read());
+
+    if (sequencer_internal_state.current_track == 0) {
+        sequencer_internal_state.timer = timer_read();
+    }
+
+    if (timer_elapsed(sequencer_internal_state.timer) < sequencer_internal_state.current_track * SEQUENCER_TRACK_THROTTLE) {
+        return;
+    }
+
+#if defined(MIDI_ENABLE) || defined(MIDI_MOCKED)
+    if (is_sequencer_step_on_for_track(sequencer_internal_state.current_step, sequencer_internal_state.current_track)) {
+        process_midi_basic_noteon(midi_compute_note(sequencer_config.track_notes[sequencer_internal_state.current_track]));
+    }
+#endif
+
+    if (sequencer_internal_state.current_track < SEQUENCER_TRACKS - 1) {
+        sequencer_internal_state.current_track++;
+    } else {
+        sequencer_internal_state.phase = SEQUENCER_PHASE_RELEASE;
+    }
+}
+
+void sequencer_phase_release(void) {
+    if (timer_elapsed(sequencer_internal_state.timer) < SEQUENCER_PHASE_RELEASE_TIMEOUT + sequencer_internal_state.current_track * SEQUENCER_TRACK_THROTTLE) {
+        return;
+    }
+#if defined(MIDI_ENABLE) || defined(MIDI_MOCKED)
+    if (is_sequencer_step_on_for_track(sequencer_internal_state.current_step, sequencer_internal_state.current_track)) {
+        process_midi_basic_noteoff(midi_compute_note(sequencer_config.track_notes[sequencer_internal_state.current_track]));
+    }
+#endif
+    if (sequencer_internal_state.current_track > 0) {
+        sequencer_internal_state.current_track--;
+    } else {
+        sequencer_internal_state.phase = SEQUENCER_PHASE_PAUSE;
+    }
+}
+
+void sequencer_phase_pause(void) {
+    if (timer_elapsed(sequencer_internal_state.timer) < sequencer_get_step_duration()) {
+        return;
+    }
+
+    sequencer_internal_state.current_step = (sequencer_internal_state.current_step + 1) % SEQUENCER_STEPS;
+    sequencer_internal_state.phase        = SEQUENCER_PHASE_ATTACK;
+}
+
+void matrix_scan_sequencer(void) {
+    if (!sequencer_config.enabled) {
+        return;
+    }
+
+    if (sequencer_internal_state.phase == SEQUENCER_PHASE_PAUSE) {
+        sequencer_phase_pause();
+    }
+
+    if (sequencer_internal_state.phase == SEQUENCER_PHASE_RELEASE) {
+        sequencer_phase_release();
+    }
+
+    if (sequencer_internal_state.phase == SEQUENCER_PHASE_ATTACK) {
+        sequencer_phase_attack();
+    }
+}
+
+uint16_t sequencer_get_beat_duration(void) { return get_beat_duration(sequencer_config.tempo); }
+
+uint16_t sequencer_get_step_duration(void) { return get_step_duration(sequencer_config.tempo, sequencer_config.resolution); }
+
+uint16_t get_beat_duration(uint8_t tempo) {
+    // Don’t crash in the unlikely case where the given tempo is 0
+    if (tempo == 0) {
+        return get_beat_duration(60);
+    }
+
+    /**
+     * Given
+     *  t = tempo and d = duration, both strictly greater than 0
+     * When
+     *  t beats / minute = 1 beat / d ms
+     * Then
+     *  t beats / 60000ms = 1 beat / d ms
+     *  d ms = 60000ms / t
+     */
+    return 60000 / tempo;
+}
+
+uint16_t get_step_duration(uint8_t tempo, sequencer_resolution_t resolution) {
+    /**
+     * Resolution cheatsheet:
+     * 1/2  => 2 steps per 4 beats
+     * 1/2T => 3 steps per 4 beats
+     * 1/4  => 4 steps per 4 beats
+     * 1/4T => 6 steps per 4 beats
+     * 1/8  => 8 steps per 4 beats
+     * 1/8T => 12 steps per 4 beats
+     * 1/16 => 16 steps per 4 beats
+     * 1/16T => 24 steps per 4 beats
+     * 1/32 => 32 steps per 4 beats
+     *
+     * The number of steps for binary resolutions follows the powers of 2.
+     * The ternary variants are simply 1.5x faster.
+     */
+    bool     is_binary            = resolution % 2 == 0;
+    uint8_t  binary_steps         = 2 << (resolution / 2);
+    uint16_t binary_step_duration = get_beat_duration(tempo) * 4 / binary_steps;
+
+    return is_binary ? binary_step_duration : 2 * binary_step_duration / 3;
+}
diff --git a/quantum/sequencer/sequencer.h b/quantum/sequencer/sequencer.h
new file mode 100644
index 0000000000..aeca7a1e9b
--- /dev/null
+++ b/quantum/sequencer/sequencer.h
@@ -0,0 +1,122 @@
+/* Copyright 2020 Rodolphe Belouin
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdbool.h>
+#include "debug.h"
+#include "timer.h"
+
+// Maximum number of steps: 256
+#ifndef SEQUENCER_STEPS
+#    define SEQUENCER_STEPS 16
+#endif
+
+// Maximum number of tracks: 8
+#ifndef SEQUENCER_TRACKS
+#    define SEQUENCER_TRACKS 8
+#endif
+
+#ifndef SEQUENCER_TRACK_THROTTLE
+#    define SEQUENCER_TRACK_THROTTLE 3
+#endif
+
+#ifndef SEQUENCER_PHASE_RELEASE_TIMEOUT
+#    define SEQUENCER_PHASE_RELEASE_TIMEOUT 30
+#endif
+
+/**
+ * Make sure that the items of this enumeration follow the powers of 2, separated by a ternary variant.
+ * Check the implementation of `get_step_duration` for further explanation.
+ */
+typedef enum { SQ_RES_2, SQ_RES_2T, SQ_RES_4, SQ_RES_4T, SQ_RES_8, SQ_RES_8T, SQ_RES_16, SQ_RES_16T, SQ_RES_32, SEQUENCER_RESOLUTIONS } sequencer_resolution_t;
+
+typedef struct {
+    bool                   enabled;
+    uint8_t                steps[SEQUENCER_STEPS];
+    uint16_t               track_notes[SEQUENCER_TRACKS];
+    uint8_t                tempo;  // Is a maximum tempo of 255 reasonable?
+    sequencer_resolution_t resolution;
+} sequencer_config_t;
+
+/**
+ * Because Digital Audio Workstations get overwhelmed when too many MIDI signals are sent concurrently,
+ * We use a "phase" state machine to delay some of the events.
+ */
+typedef enum sequencer_phase_t {
+    SEQUENCER_PHASE_ATTACK,   // t=0ms, send the MIDI note on signal
+    SEQUENCER_PHASE_RELEASE,  // t=SEQUENCER_PHASE_RELEASE_TIMEOUT ms, send the MIDI note off signal
+    SEQUENCER_PHASE_PAUSE     // t=step duration ms, loop
+} sequencer_phase_t;
+
+typedef struct {
+    uint8_t           active_tracks;
+    uint8_t           current_track;
+    uint8_t           current_step;
+    uint16_t          timer;
+    sequencer_phase_t phase;
+} sequencer_state_t;
+
+extern sequencer_config_t sequencer_config;
+
+// We expose the internal state to make the feature more "unit-testable"
+extern sequencer_state_t sequencer_internal_state;
+
+bool is_sequencer_on(void);
+void sequencer_toggle(void);
+void sequencer_on(void);
+void sequencer_off(void);
+
+void sequencer_set_track_notes(const uint16_t track_notes[SEQUENCER_TRACKS]);
+
+bool is_sequencer_track_active(uint8_t track);
+void sequencer_set_track_activation(uint8_t track, bool value);
+void sequencer_toggle_track_activation(uint8_t track);
+void sequencer_toggle_single_active_track(uint8_t track);
+
+#define sequencer_activate_track(track) sequencer_set_track_activation(track, true)
+#define sequencer_deactivate_track(track) sequencer_set_track_activation(track, false)
+
+bool is_sequencer_step_on(uint8_t step);
+bool is_sequencer_step_on_for_track(uint8_t step, uint8_t track);
+void sequencer_set_step(uint8_t step, bool value);
+void sequencer_toggle_step(uint8_t step);
+void sequencer_set_all_steps(bool value);
+
+#define sequencer_set_step_on(step) sequencer_set_step(step, true)
+#define sequencer_set_step_off(step) sequencer_set_step(step, false)
+#define sequencer_set_all_steps_on() sequencer_set_all_steps(true)
+#define sequencer_set_all_steps_off() sequencer_set_all_steps(false)
+
+uint8_t sequencer_get_tempo(void);
+void    sequencer_set_tempo(uint8_t tempo);
+void    sequencer_increase_tempo(void);
+void    sequencer_decrease_tempo(void);
+
+sequencer_resolution_t sequencer_get_resolution(void);
+void                   sequencer_set_resolution(sequencer_resolution_t resolution);
+void                   sequencer_increase_resolution(void);
+void                   sequencer_decrease_resolution(void);
+
+uint8_t sequencer_get_current_step(void);
+
+uint16_t sequencer_get_beat_duration(void);
+uint16_t sequencer_get_step_duration(void);
+
+uint16_t get_beat_duration(uint8_t tempo);
+uint16_t get_step_duration(uint8_t tempo, sequencer_resolution_t resolution);
+
+void matrix_scan_sequencer(void);
diff --git a/quantum/sequencer/tests/midi_mock.c b/quantum/sequencer/tests/midi_mock.c
new file mode 100644
index 0000000000..236e16f9d7
--- /dev/null
+++ b/quantum/sequencer/tests/midi_mock.c
@@ -0,0 +1,26 @@
+/* Copyright 2020 Rodolphe Belouin
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "midi_mock.h"
+
+uint16_t last_noteon  = 0;
+uint16_t last_noteoff = 0;
+
+uint16_t midi_compute_note(uint16_t keycode) { return keycode; }
+
+void process_midi_basic_noteon(uint16_t note) { last_noteon = note; }
+
+void process_midi_basic_noteoff(uint16_t note) { last_noteoff = note; }
diff --git a/quantum/sequencer/tests/midi_mock.h b/quantum/sequencer/tests/midi_mock.h
new file mode 100644
index 0000000000..4d8c2eb307
--- /dev/null
+++ b/quantum/sequencer/tests/midi_mock.h
@@ -0,0 +1,26 @@
+/* Copyright 2020 Rodolphe Belouin
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+extern uint16_t last_noteon;
+extern uint16_t last_noteoff;
+
+uint16_t midi_compute_note(uint16_t keycode);
+void     process_midi_basic_noteon(uint16_t note);
+void     process_midi_basic_noteoff(uint16_t note);
diff --git a/quantum/sequencer/tests/rules.mk b/quantum/sequencer/tests/rules.mk
new file mode 100644
index 0000000000..76c221cf92
--- /dev/null
+++ b/quantum/sequencer/tests/rules.mk
@@ -0,0 +1,11 @@
+# The letter case of these variables might seem odd. However:
+# - it is consistent with the serial_link example that is used as a reference in the Unit Testing article (https://docs.qmk.fm/#/unit_testing?id=adding-tests-for-new-or-existing-features)
+# - Neither `make test:sequencer` or `make test:SEQUENCER` work when using SCREAMING_SNAKE_CASE
+
+sequencer_DEFS := -DNO_DEBUG -DMIDI_MOCKED
+
+sequencer_SRC := \
+	$(QUANTUM_PATH)/sequencer/tests/midi_mock.c \
+	$(QUANTUM_PATH)/sequencer/tests/sequencer_tests.cpp \
+	$(QUANTUM_PATH)/sequencer/sequencer.c \
+	$(TMK_PATH)/common/test/timer.c
diff --git a/quantum/sequencer/tests/sequencer_tests.cpp b/quantum/sequencer/tests/sequencer_tests.cpp
new file mode 100644
index 0000000000..e81984e5b5
--- /dev/null
+++ b/quantum/sequencer/tests/sequencer_tests.cpp
@@ -0,0 +1,590 @@
+/* Copyright 2020 Rodolphe Belouin
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "gtest/gtest.h"
+
+extern "C" {
+#include "sequencer.h"
+#include "midi_mock.h"
+#include "quantum/quantum_keycodes.h"
+}
+
+extern "C" {
+void set_time(uint32_t t);
+void advance_time(uint32_t ms);
+}
+
+class SequencerTest : public ::testing::Test {
+   protected:
+    void SetUp() override {
+        config_copy.enabled = sequencer_config.enabled;
+
+        for (int i = 0; i < SEQUENCER_STEPS; i++) {
+            config_copy.steps[i] = sequencer_config.steps[i];
+        }
+
+        for (int i = 0; i < SEQUENCER_TRACKS; i++) {
+            config_copy.track_notes[i] = sequencer_config.track_notes[i];
+        }
+
+        config_copy.tempo      = sequencer_config.tempo;
+        config_copy.resolution = sequencer_config.resolution;
+
+        state_copy.active_tracks = sequencer_internal_state.active_tracks;
+        state_copy.current_track = sequencer_internal_state.current_track;
+        state_copy.current_step  = sequencer_internal_state.current_step;
+        state_copy.timer         = sequencer_internal_state.timer;
+
+        last_noteon  = 0;
+        last_noteoff = 0;
+
+        set_time(0);
+    }
+
+    void TearDown() override {
+        sequencer_config.enabled = config_copy.enabled;
+
+        for (int i = 0; i < SEQUENCER_STEPS; i++) {
+            sequencer_config.steps[i] = config_copy.steps[i];
+        }
+
+        for (int i = 0; i < SEQUENCER_TRACKS; i++) {
+            sequencer_config.track_notes[i] = config_copy.track_notes[i];
+        }
+
+        sequencer_config.tempo      = config_copy.tempo;
+        sequencer_config.resolution = config_copy.resolution;
+
+        sequencer_internal_state.active_tracks = state_copy.active_tracks;
+        sequencer_internal_state.current_track = state_copy.current_track;
+        sequencer_internal_state.current_step  = state_copy.current_step;
+        sequencer_internal_state.timer         = state_copy.timer;
+    }
+
+    sequencer_config_t config_copy;
+    sequencer_state_t  state_copy;
+};
+
+TEST_F(SequencerTest, TestOffByDefault) { EXPECT_EQ(is_sequencer_on(), false); }
+
+TEST_F(SequencerTest, TestOn) {
+    sequencer_config.enabled = false;
+
+    sequencer_on();
+    EXPECT_EQ(is_sequencer_on(), true);
+
+    // sequencer_on is idempotent
+    sequencer_on();
+    EXPECT_EQ(is_sequencer_on(), true);
+}
+
+TEST_F(SequencerTest, TestOff) {
+    sequencer_config.enabled = true;
+
+    sequencer_off();
+    EXPECT_EQ(is_sequencer_on(), false);
+
+    // sequencer_off is idempotent
+    sequencer_off();
+    EXPECT_EQ(is_sequencer_on(), false);
+}
+
+TEST_F(SequencerTest, TestToggle) {
+    sequencer_config.enabled = false;
+
+    sequencer_toggle();
+    EXPECT_EQ(is_sequencer_on(), true);
+
+    sequencer_toggle();
+    EXPECT_EQ(is_sequencer_on(), false);
+}
+
+TEST_F(SequencerTest, TestNoActiveTrackByDefault) {
+    for (int i = 0; i < SEQUENCER_TRACKS; i++) {
+        EXPECT_EQ(is_sequencer_track_active(i), false);
+    }
+}
+
+TEST_F(SequencerTest, TestGetActiveTracks) {
+    sequencer_internal_state.active_tracks = (1 << 7) + (1 << 6) + (1 << 3) + (1 << 1) + (1 << 0);
+
+    EXPECT_EQ(is_sequencer_track_active(0), true);
+    EXPECT_EQ(is_sequencer_track_active(1), true);
+    EXPECT_EQ(is_sequencer_track_active(2), false);
+    EXPECT_EQ(is_sequencer_track_active(3), true);
+    EXPECT_EQ(is_sequencer_track_active(4), false);
+    EXPECT_EQ(is_sequencer_track_active(5), false);
+    EXPECT_EQ(is_sequencer_track_active(6), true);
+    EXPECT_EQ(is_sequencer_track_active(7), true);
+}
+
+TEST_F(SequencerTest, TestGetActiveTracksOutOfBound) {
+    sequencer_set_track_activation(-1, true);
+    sequencer_set_track_activation(8, true);
+
+    EXPECT_EQ(is_sequencer_track_active(-1), false);
+    EXPECT_EQ(is_sequencer_track_active(8), false);
+}
+
+TEST_F(SequencerTest, TestToggleTrackActivation) {
+    sequencer_internal_state.active_tracks = (1 << 7) + (1 << 6) + (1 << 3) + (1 << 1) + (1 << 0);
+
+    sequencer_toggle_track_activation(6);
+
+    EXPECT_EQ(is_sequencer_track_active(0), true);
+    EXPECT_EQ(is_sequencer_track_active(1), true);
+    EXPECT_EQ(is_sequencer_track_active(2), false);
+    EXPECT_EQ(is_sequencer_track_active(3), true);
+    EXPECT_EQ(is_sequencer_track_active(4), false);
+    EXPECT_EQ(is_sequencer_track_active(5), false);
+    EXPECT_EQ(is_sequencer_track_active(6), false);
+    EXPECT_EQ(is_sequencer_track_active(7), true);
+}
+
+TEST_F(SequencerTest, TestToggleSingleTrackActivation) {
+    sequencer_internal_state.active_tracks = (1 << 7) + (1 << 6) + (1 << 3) + (1 << 1) + (1 << 0);
+
+    sequencer_toggle_single_active_track(2);
+
+    EXPECT_EQ(is_sequencer_track_active(0), false);
+    EXPECT_EQ(is_sequencer_track_active(1), false);
+    EXPECT_EQ(is_sequencer_track_active(2), true);
+    EXPECT_EQ(is_sequencer_track_active(3), false);
+    EXPECT_EQ(is_sequencer_track_active(4), false);
+    EXPECT_EQ(is_sequencer_track_active(5), false);
+    EXPECT_EQ(is_sequencer_track_active(6), false);
+    EXPECT_EQ(is_sequencer_track_active(7), false);
+}
+
+TEST_F(SequencerTest, TestStepOffByDefault) {
+    for (int i = 0; i < SEQUENCER_STEPS; i++) {
+        EXPECT_EQ(is_sequencer_step_on(i), false);
+    }
+}
+
+TEST_F(SequencerTest, TestIsStepOffWithNoActiveTracks) {
+    sequencer_config.steps[3] = 0xFF;
+    EXPECT_EQ(is_sequencer_step_on(3), false);
+}
+
+TEST_F(SequencerTest, TestIsStepOffWithGivenActiveTracks) {
+    sequencer_set_track_activation(2, true);
+    sequencer_set_track_activation(3, true);
+
+    sequencer_config.steps[3] = (1 << 0) + (1 << 1);
+
+    // No active tracks have the step enabled, so it is off
+    EXPECT_EQ(is_sequencer_step_on(3), false);
+}
+
+TEST_F(SequencerTest, TestIsStepOnWithGivenActiveTracks) {
+    sequencer_set_track_activation(2, true);
+    sequencer_set_track_activation(3, true);
+
+    sequencer_config.steps[3] = (1 << 2);
+
+    // Track 2 has the step enabled, so it is on
+    EXPECT_EQ(is_sequencer_step_on(3), true);
+}
+
+TEST_F(SequencerTest, TestIsStepOffForGivenTrack) {
+    sequencer_config.steps[3] = 0x00;
+    EXPECT_EQ(is_sequencer_step_on_for_track(3, 5), false);
+}
+
+TEST_F(SequencerTest, TestIsStepOnForGivenTrack) {
+    sequencer_config.steps[3] = (1 << 5);
+    EXPECT_EQ(is_sequencer_step_on_for_track(3, 5), true);
+}
+
+TEST_F(SequencerTest, TestSetStepOn) {
+    sequencer_internal_state.active_tracks = (1 << 6) + (1 << 3) + (1 << 2);
+    sequencer_config.steps[2]              = (1 << 5) + (1 << 2);
+
+    sequencer_set_step(2, true);
+
+    EXPECT_EQ(sequencer_config.steps[2], (1 << 6) + (1 << 5) + (1 << 3) + (1 << 2));
+}
+
+TEST_F(SequencerTest, TestSetStepOff) {
+    sequencer_internal_state.active_tracks = (1 << 6) + (1 << 3) + (1 << 2);
+    sequencer_config.steps[2]              = (1 << 5) + (1 << 2);
+
+    sequencer_set_step(2, false);
+
+    EXPECT_EQ(sequencer_config.steps[2], (1 << 5));
+}
+
+TEST_F(SequencerTest, TestToggleStepOff) {
+    sequencer_internal_state.active_tracks = (1 << 6) + (1 << 3) + (1 << 2);
+    sequencer_config.steps[2]              = (1 << 5) + (1 << 2);
+
+    sequencer_toggle_step(2);
+
+    EXPECT_EQ(sequencer_config.steps[2], (1 << 5));
+}
+
+TEST_F(SequencerTest, TestToggleStepOn) {
+    sequencer_internal_state.active_tracks = (1 << 6) + (1 << 3) + (1 << 2);
+    sequencer_config.steps[2]              = 0;
+
+    sequencer_toggle_step(2);
+
+    EXPECT_EQ(sequencer_config.steps[2], (1 << 6) + (1 << 3) + (1 << 2));
+}
+
+TEST_F(SequencerTest, TestSetAllStepsOn) {
+    sequencer_internal_state.active_tracks = (1 << 6) + (1 << 3) + (1 << 2);
+    sequencer_config.steps[2]              = (1 << 7) + (1 << 6);
+    sequencer_config.steps[4]              = (1 << 3) + (1 << 1);
+
+    sequencer_set_all_steps(true);
+
+    EXPECT_EQ(sequencer_config.steps[2], (1 << 7) + (1 << 6) + (1 << 3) + (1 << 2));
+    EXPECT_EQ(sequencer_config.steps[4], (1 << 6) + (1 << 3) + (1 << 2) + (1 << 1));
+}
+
+TEST_F(SequencerTest, TestSetAllStepsOff) {
+    sequencer_internal_state.active_tracks = (1 << 6) + (1 << 3) + (1 << 2);
+    sequencer_config.steps[2]              = (1 << 7) + (1 << 6);
+    sequencer_config.steps[4]              = (1 << 3) + (1 << 1);
+
+    sequencer_set_all_steps(false);
+
+    EXPECT_EQ(sequencer_config.steps[2], (1 << 7));
+    EXPECT_EQ(sequencer_config.steps[4], (1 << 1));
+}
+
+TEST_F(SequencerTest, TestSetTempoZero) {
+    sequencer_config.tempo = 123;
+
+    sequencer_set_tempo(0);
+
+    EXPECT_EQ(sequencer_config.tempo, 123);
+}
+
+TEST_F(SequencerTest, TestIncreaseTempoMax) {
+    sequencer_config.tempo = UINT8_MAX;
+
+    sequencer_increase_tempo();
+
+    EXPECT_EQ(sequencer_config.tempo, UINT8_MAX);
+}
+
+TEST_F(SequencerTest, TestSetResolutionLowerBound) {
+    sequencer_config.resolution = SQ_RES_4;
+
+    sequencer_set_resolution((sequencer_resolution_t)-1);
+
+    EXPECT_EQ(sequencer_config.resolution, SQ_RES_4);
+}
+
+TEST_F(SequencerTest, TestSetResolutionUpperBound) {
+    sequencer_config.resolution = SQ_RES_4;
+
+    sequencer_set_resolution(SEQUENCER_RESOLUTIONS);
+
+    EXPECT_EQ(sequencer_config.resolution, SQ_RES_4);
+}
+
+TEST_F(SequencerTest, TestGetBeatDuration) {
+    EXPECT_EQ(get_beat_duration(60), 1000);
+    EXPECT_EQ(get_beat_duration(120), 500);
+    EXPECT_EQ(get_beat_duration(240), 250);
+    EXPECT_EQ(get_beat_duration(0), 1000);
+}
+
+TEST_F(SequencerTest, TestGetStepDuration60) {
+    /**
+     * Resolution cheatsheet:
+     * 1/2  => 2 steps per 4 beats
+     * 1/2T => 3 steps per 4 beats
+     * 1/4  => 4 steps per 4 beats
+     * 1/4T => 6 steps per 4 beats
+     * 1/8  => 8 steps per 4 beats
+     * 1/8T => 12 steps per 4 beats
+     * 1/16 => 16 steps per 4 beats
+     * 1/16T => 24 steps per 4 beats
+     * 1/32 => 32 steps per 4 beats
+     *
+     * The number of steps for binary resolutions follows the powers of 2.
+     * The ternary variants are simply 1.5x faster.
+     */
+    EXPECT_EQ(get_step_duration(60, SQ_RES_2), 2000);
+    EXPECT_EQ(get_step_duration(60, SQ_RES_4), 1000);
+    EXPECT_EQ(get_step_duration(60, SQ_RES_8), 500);
+    EXPECT_EQ(get_step_duration(60, SQ_RES_16), 250);
+    EXPECT_EQ(get_step_duration(60, SQ_RES_32), 125);
+
+    EXPECT_EQ(get_step_duration(60, SQ_RES_2T), 1333);
+    EXPECT_EQ(get_step_duration(60, SQ_RES_4T), 666);
+    EXPECT_EQ(get_step_duration(60, SQ_RES_8T), 333);
+    EXPECT_EQ(get_step_duration(60, SQ_RES_16T), 166);
+}
+
+TEST_F(SequencerTest, TestGetStepDuration120) {
+    /**
+     * Resolution cheatsheet:
+     * 1/2  => 2 steps per 4 beats
+     * 1/2T => 3 steps per 4 beats
+     * 1/4  => 4 steps per 4 beats
+     * 1/4T => 6 steps per 4 beats
+     * 1/8  => 8 steps per 4 beats
+     * 1/8T => 12 steps per 4 beats
+     * 1/16 => 16 steps per 4 beats
+     * 1/16T => 24 steps per 4 beats
+     * 1/32 => 32 steps per 4 beats
+     *
+     * The number of steps for binary resolutions follows the powers of 2.
+     * The ternary variants are simply 1.5x faster.
+     */
+    EXPECT_EQ(get_step_duration(30, SQ_RES_2), 4000);
+    EXPECT_EQ(get_step_duration(30, SQ_RES_4), 2000);
+    EXPECT_EQ(get_step_duration(30, SQ_RES_8), 1000);
+    EXPECT_EQ(get_step_duration(30, SQ_RES_16), 500);
+    EXPECT_EQ(get_step_duration(30, SQ_RES_32), 250);
+
+    EXPECT_EQ(get_step_duration(30, SQ_RES_2T), 2666);
+    EXPECT_EQ(get_step_duration(30, SQ_RES_4T), 1333);
+    EXPECT_EQ(get_step_duration(30, SQ_RES_8T), 666);
+    EXPECT_EQ(get_step_duration(30, SQ_RES_16T), 333);
+}
+
+void setUpMatrixScanSequencerTest(void) {
+    sequencer_config.enabled    = true;
+    sequencer_config.tempo      = 120;
+    sequencer_config.resolution = SQ_RES_16;
+
+    // Configure the notes for each track
+    sequencer_config.track_notes[0] = MI_C;
+    sequencer_config.track_notes[1] = MI_D;
+    sequencer_config.track_notes[2] = MI_E;
+    sequencer_config.track_notes[3] = MI_F;
+    sequencer_config.track_notes[4] = MI_G;
+    sequencer_config.track_notes[5] = MI_A;
+    sequencer_config.track_notes[6] = MI_B;
+    sequencer_config.track_notes[7] = MI_C;
+
+    // Turn on some steps
+    sequencer_config.steps[0] = (1 << 0);
+    sequencer_config.steps[2] = (1 << 1) + (1 << 0);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldAttackFirstTrackOfFirstStep) {
+    setUpMatrixScanSequencerTest();
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(last_noteon, MI_C);
+    EXPECT_EQ(last_noteoff, 0);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldAttackSecondTrackAfterFirstTrackOfFirstStep) {
+    setUpMatrixScanSequencerTest();
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(sequencer_internal_state.current_step, 0);
+    EXPECT_EQ(sequencer_internal_state.current_track, 1);
+    EXPECT_EQ(sequencer_internal_state.phase, SEQUENCER_PHASE_ATTACK);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldNotAttackInactiveTrackFirstStep) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = 0;
+    sequencer_internal_state.current_track = 1;
+
+    // Wait some time after the first track has been attacked
+    advance_time(SEQUENCER_TRACK_THROTTLE);
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(last_noteon, 0);
+    EXPECT_EQ(last_noteoff, 0);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldAttackThirdTrackAfterSecondTrackOfFirstStep) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = 0;
+    sequencer_internal_state.current_track = 1;
+
+    // Wait some time after the second track has been attacked
+    advance_time(2 * SEQUENCER_TRACK_THROTTLE);
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(sequencer_internal_state.current_step, 0);
+    EXPECT_EQ(sequencer_internal_state.current_track, 2);
+    EXPECT_EQ(sequencer_internal_state.phase, SEQUENCER_PHASE_ATTACK);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldEnterReleasePhaseAfterLastTrackHasBeenProcessedFirstStep) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = 0;
+    sequencer_internal_state.current_track = SEQUENCER_TRACKS - 1;
+
+    // Wait until all notes have been attacked
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(last_noteon, 0);
+    EXPECT_EQ(last_noteoff, 0);
+    EXPECT_EQ(sequencer_internal_state.current_step, 0);
+    EXPECT_EQ(sequencer_internal_state.current_track, SEQUENCER_TRACKS - 1);
+    EXPECT_EQ(sequencer_internal_state.phase, SEQUENCER_PHASE_RELEASE);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldReleaseBackwards) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = 0;
+    sequencer_internal_state.current_track = SEQUENCER_TRACKS - 1;
+    sequencer_internal_state.phase         = SEQUENCER_PHASE_RELEASE;
+
+    // Wait until all notes have been attacked
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+    // + the release timeout
+    advance_time(SEQUENCER_PHASE_RELEASE_TIMEOUT);
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(sequencer_internal_state.current_step, 0);
+    EXPECT_EQ(sequencer_internal_state.current_track, SEQUENCER_TRACKS - 2);
+    EXPECT_EQ(sequencer_internal_state.phase, SEQUENCER_PHASE_RELEASE);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldNotReleaseInactiveTrackFirstStep) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = 0;
+    sequencer_internal_state.current_track = SEQUENCER_TRACKS - 1;
+    sequencer_internal_state.phase         = SEQUENCER_PHASE_RELEASE;
+
+    // Wait until all notes have been attacked
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+    // + the release timeout
+    advance_time(SEQUENCER_PHASE_RELEASE_TIMEOUT);
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(last_noteon, 0);
+    EXPECT_EQ(last_noteoff, 0);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldReleaseFirstTrackFirstStep) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = 0;
+    sequencer_internal_state.current_track = 0;
+    sequencer_internal_state.phase         = SEQUENCER_PHASE_RELEASE;
+
+    // Wait until all notes have been attacked
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+    // + the release timeout
+    advance_time(SEQUENCER_PHASE_RELEASE_TIMEOUT);
+    // + all the other notes have been released
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(last_noteon, 0);
+    EXPECT_EQ(last_noteoff, MI_C);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldEnterPausePhaseAfterRelease) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = 0;
+    sequencer_internal_state.current_track = 0;
+    sequencer_internal_state.phase         = SEQUENCER_PHASE_RELEASE;
+
+    // Wait until all notes have been attacked
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+    // + the release timeout
+    advance_time(SEQUENCER_PHASE_RELEASE_TIMEOUT);
+    // + all the other notes have been released
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(sequencer_internal_state.current_step, 0);
+    EXPECT_EQ(sequencer_internal_state.current_track, 0);
+    EXPECT_EQ(sequencer_internal_state.phase, SEQUENCER_PHASE_PAUSE);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldProcessFirstTrackOfSecondStepAfterPause) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = 0;
+    sequencer_internal_state.current_track = 0;
+    sequencer_internal_state.phase         = SEQUENCER_PHASE_PAUSE;
+
+    // Wait until all notes have been attacked
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+    // + the release timeout
+    advance_time(SEQUENCER_PHASE_RELEASE_TIMEOUT);
+    // + all the other notes have been released
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+    // + the step duration (one 16th at tempo=120 lasts 125ms)
+    advance_time(125);
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(sequencer_internal_state.current_step, 1);
+    EXPECT_EQ(sequencer_internal_state.current_track, 1);
+    EXPECT_EQ(sequencer_internal_state.phase, SEQUENCER_PHASE_ATTACK);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldProcessSecondTrackTooEarly) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = 2;
+    sequencer_internal_state.current_track = 1;
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(last_noteon, 0);
+    EXPECT_EQ(last_noteoff, 0);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldProcessSecondTrackOnTime) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = 2;
+    sequencer_internal_state.current_track = 1;
+
+    // Wait until first track has been attacked
+    advance_time(SEQUENCER_TRACK_THROTTLE);
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(last_noteon, MI_D);
+    EXPECT_EQ(last_noteoff, 0);
+}
+
+TEST_F(SequencerTest, TestMatrixScanSequencerShouldLoopOnceSequenceIsOver) {
+    setUpMatrixScanSequencerTest();
+
+    sequencer_internal_state.current_step  = SEQUENCER_STEPS - 1;
+    sequencer_internal_state.current_track = 0;
+    sequencer_internal_state.phase         = SEQUENCER_PHASE_PAUSE;
+
+    // Wait until all notes have been attacked
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+    // + the release timeout
+    advance_time(SEQUENCER_PHASE_RELEASE_TIMEOUT);
+    // + all the other notes have been released
+    advance_time((SEQUENCER_TRACKS - 1) * SEQUENCER_TRACK_THROTTLE);
+    // + the step duration (one 16th at tempo=120 lasts 125ms)
+    advance_time(125);
+
+    matrix_scan_sequencer();
+    EXPECT_EQ(sequencer_internal_state.current_step, 0);
+    EXPECT_EQ(sequencer_internal_state.current_track, 1);
+    EXPECT_EQ(sequencer_internal_state.phase, SEQUENCER_PHASE_ATTACK);
+}
diff --git a/quantum/sequencer/tests/testlist.mk b/quantum/sequencer/tests/testlist.mk
new file mode 100644
index 0000000000..bb38991109
--- /dev/null
+++ b/quantum/sequencer/tests/testlist.mk
@@ -0,0 +1 @@
+TEST_LIST += sequencer
diff --git a/testlist.mk b/testlist.mk
index d949fb3eae..ca1408806c 100644
--- a/testlist.mk
+++ b/testlist.mk
@@ -1,6 +1,7 @@
 TEST_LIST = $(notdir $(patsubst %/rules.mk,%,$(wildcard $(ROOT_DIR)/tests/*/rules.mk)))
 FULL_TESTS := $(TEST_LIST)
 
+include $(ROOT_DIR)/quantum/sequencer/tests/testlist.mk
 include $(ROOT_DIR)/quantum/serial_link/tests/testlist.mk
 
 define VALIDATE_TEST_LIST