2020 November 28 Breaking Changes Update (#11053)

* Branch point for 2020 November 28 Breaking Change                                                

* Remove matrix_col_t to allow MATRIX_ROWS > 32 (#10183)                                           

* Add support for soft serial to ATmega32U2 (#10204)                                               

* Change MIDI velocity implementation to allow direct control of velocity value (#9940)            

* Add ability to build a subset of all keyboards based on platform.                                

* Actually use eeprom_driver_init().                                                               

* Make bootloader_jump weak for ChibiOS. (#10417)                                                  

* Joystick 16-bit support (#10439)                                                                 

* Per-encoder resolutions (#10259)                                                                 

* Share button state from mousekey to pointing_device (#10179)                                     

* Add hotfix for chibios keyboards not wake (#10088)                                               

* Add advanced/efficient RGB Matrix Indicators (#8564)                                             

* Naming change.                                                                                   

* Support for STM32 GPIOF,G,H,I,J,K (#10206)                                                       

* Add milc as a dependency and remove the installed milc (#10563)                                  

* ChibiOS upgrade: early init conversions (#10214)                                                 

* ChibiOS upgrade: configuration file migrator (#9952)                                             

* Haptic and solenoid cleanup (#9700)                                                              

* XD75 cleanup (#10524)                                                                            

* OLED display update interval support (#10388)                                                    

* Add definition based on currently-selected serial driver. (#10716)                               

* New feature: Retro Tapping per key (#10622)                                                      

* Allow for modification of output RGB values when using rgblight/rgb_matrix. (#10638)             

* Add housekeeping task callbacks so that keyboards/keymaps are capable of executing code for each main loop iteration. (#10530)

* Rescale both ChibiOS and AVR backlighting.                                                       

* Reduce Helix keyboard build variation (#8669)                                                    

* Minor change to behavior allowing display updates to continue between task ticks (#10750)        

* Some GPIO manipulations in matrix.c change to atomic. (#10491)                                   

* qmk cformat (#10767)                                                                             

* [Keyboard] Update the Speedo firmware for v3.0 (#10657)                                          

* Maartenwut/Maarten namechange to evyd13/Evy (#10274)                                             

* [quantum] combine repeated lines of code (#10837)                                                

* Add step sequencer feature (#9703)                                                               

* aeboards/ext65 refactor (#10820)                                                                 

* Refactor xelus/dawn60 for Rev2 later (#10584)                                                    

* add DEBUG_MATRIX_SCAN_RATE_ENABLE to common_features.mk (#10824)                                 

* [Core] Added `add_oneshot_mods` & `del_oneshot_mods` (#10549)                                    

* update chibios os usb for the otg driver (#8893)                                                 

* Remove HD44780 References, Part 4 (#10735)                                                       

* [Keyboard] Add Valor FRL TKL (+refactor) (#10512)                                                

* Fix cursor position bug in oled_write_raw functions (#10800)                                     

* Fixup version.h writing when using SKIP_VERSION=yes (#10972)                                     

* Allow for certain code in the codebase assuming length of string. (#10974)                       

* Add AT90USB support for serial.c (#10706)                                                        

* Auto shift: support repeats and early registration (#9826)                                       

* Rename ledmatrix.h to match .c file (#7949)                                                      

* Split RGB_MATRIX_ENABLE into _ENABLE and _DRIVER (#10231)                                        

* Split LED_MATRIX_ENABLE into _ENABLE and _DRIVER (#10840)                                        

* Merge point for 2020 Nov 28 Breaking Change                                                      

1 files changed, 88 insertions, 0 deletions

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 |
+