[Core] Split support for pointing devices. (#15304)

* Draft implementation

* formatting

* fix combined buttons

* remove pimoroni throttle

* sync pointing on a throttle loop with checksum

* no longer used

* doh

Co-authored-by: Drashna Jaelre <drashna@live.com>

* switch pimoroni to a cpi equivalent

* add cpi support

* allow user modification of seperate mouse reports

* a little tidy up

* add *_RIGHT defines.

* docs

* doxygen comments

* basic changelog

* clean up pimoroni

* small doc fixes

* Update docs/feature_pointing_device.md

Co-authored-by: Drashna Jaelre <drashna@live.com>

* performance tweak if side has usb

* Don't run init funtions on wrong side

* renamed some variables for consistency

* fix pimoroni typos

* Clamp instead of OR

* Promote combined values to uint16_t

* Update pointing_device.c

Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Nick Brassel <nick@tzarc.org>

3 files changed, 126 insertions, 11 deletions

diff --git a/docs/ChangeLog/20220226/PR15304.md b/docs/ChangeLog/20220226/PR15304.md
new file mode 100644
index 0000000000..3cdb40db10
--- /dev/null
+++ b/docs/ChangeLog/20220226/PR15304.md
@@ -0,0 +1,13 @@
+### Split Common core now supports Pointing Devices ([#15304](https://github.com/qmk/qmk_firmware/pull/15304))
+
+Pointing devices can now be shared across a split keyboard with support for a single pointing device or a pointing device on each side.
+
+This feature can be enabled with `#define SPLIT_POINTING_ENABLE` and one of the following options:
+
+| Setting                   | Description                        |
+|---------------------------|------------------------------------|
+|`POINTING_DEVICE_LEFT`     | Pointing device on the left side   |
+|`POINTING_DEVICE_RIGHT`    | Pointing device on the right side  |
+|`POINTING_DEVICE_COMBINED` | Pointing device on both sides      |
+
+See the [Pointing Device](../feature_pointing_device.md) documentation for further configuration options.
diff --git a/docs/feature_pointing_device.md b/docs/feature_pointing_device.md
index 5aef9bea27..f8de92f3b4 100644
--- a/docs/feature_pointing_device.md
+++ b/docs/feature_pointing_device.md
@@ -127,11 +127,10 @@ The Pimoroni Trackball module is a I2C based breakout board with an RGB enable t
 | Setting                             | Description                                                                        | Default |
 |-------------------------------------|------------------------------------------------------------------------------------|---------|
 |`PIMORONI_TRACKBALL_ADDRESS`         | (Required) Sets the I2C Address for the Pimoroni Trackball.                        | `0x0A`  |
-|`PIMORONI_TRACKBALL_TIMEOUT`         | (Optional) The timeout for i2c communication with the trackpad in milliseconds.    | `100`   |
-|`PIMORONI_TRACKBALL_INTERVAL_MS`     | (Optional) The update/read interval for the sensor in milliseconds.                | `8`     |
+|`PIMORONI_TRACKBALL_TIMEOUT`         | (Optional) The timeout for i2c communication with the trackball in milliseconds.   | `100`   |
 |`PIMORONI_TRACKBALL_SCALE`           | (Optional) The multiplier used to generate reports from the sensor.                | `5`     |
 |`PIMORONI_TRACKBALL_DEBOUNCE_CYCLES` | (Optional) The number of scan cycles used for debouncing on the ball press.        | `20`    |
-|`PIMORONI_TRACKBALL_ERROR_COUNT`     | (Optional) Specifies the number of read/write errors until the sensor is disabled. | `10`  |
+|`PIMORONI_TRACKBALL_ERROR_COUNT`     | (Optional) Specifies the number of read/write errors until the sensor is disabled. | `10`    |
 
 ### PMW 3360 Sensor
 
@@ -171,14 +170,35 @@ void           pointing_device_driver_set_cpi(uint16_t cpi) {}
 
 ## Common Configuration
 
-| Setting                       | Description                                                           | Default       |
-|-------------------------------|-----------------------------------------------------------------------|---------------|
-|`POINTING_DEVICE_ROTATION_90`  | (Optional) Rotates the X and Y data by  90 degrees.                   | _not defined_ |
-|`POINTING_DEVICE_ROTATION_180` | (Optional) Rotates the X and Y data by 180 degrees.                   | _not defined_ |
-|`POINTING_DEVICE_ROTATION_270` | (Optional) Rotates the X and Y data by 270 degrees.                   | _not defined_ |
-|`POINTING_DEVICE_INVERT_X`     | (Optional) Inverts the X axis report.                                 | _not defined_ |
-|`POINTING_DEVICE_INVERT_Y`     | (Optional) Inverts the Y axis report.                                 | _not defined_ |
-|`POINTING_DEVICE_MOTION_PIN`   | (Optional) If supported, will only read from sensor if pin is active. | _not defined_ |
+| Setting                          | Description                                                           | Default           |
+|----------------------------------|-----------------------------------------------------------------------|-------------------|
+|`POINTING_DEVICE_ROTATION_90`     | (Optional) Rotates the X and Y data by  90 degrees.                   | _not defined_     |
+|`POINTING_DEVICE_ROTATION_180`    | (Optional) Rotates the X and Y data by 180 degrees.                   | _not defined_     |
+|`POINTING_DEVICE_ROTATION_270`    | (Optional) Rotates the X and Y data by 270 degrees.                   | _not defined_     |
+|`POINTING_DEVICE_INVERT_X`        | (Optional) Inverts the X axis report.                                 | _not defined_     |
+|`POINTING_DEVICE_INVERT_Y`        | (Optional) Inverts the Y axis report.                                 | _not defined_     |
+|`POINTING_DEVICE_MOTION_PIN`      | (Optional) If supported, will only read from sensor if pin is active. | _not defined_     |
+|`POINTING_DEVICE_TASK_THROTTLE_MS`      | (Optional) Limits the frequency that the sensor is polled for motion. | _not defined_     |
+
+!> When using `SPLIT_POINTING_ENABLE` the `POINTING_DEVICE_MOTION_PIN` functionality is not supported and would recommend `POINTING_DEVICE_TASK_THROTTLE_MS` be set to `1`. Increasing this value will increase transport performance at the cost of possible mouse responsiveness.
+
+
+## Split Keyboard Configuration
+
+The following configuration options are only available when using `SPLIT_POINTING_ENABLE` see [data sync options](feature_split_keyboard.md?id=data-sync-options). The rotation and invert `*_RIGHT` options are only used with `POINTING_DEVICE_COMBINED`. If using `POINTING_DEVICE_LEFT` or `POINTING_DEVICE_RIGHT` use the common configuration above to configure your pointing device.
+
+| Setting                                | Description                                                           | Default       |
+|----------------------------------------|-----------------------------------------------------------------------|---------------|
+|`POINTING_DEVICE_LEFT`                  | Pointing device on the left side (Required - pick one only)           | _not defined_ |
+|`POINTING_DEVICE_RIGHT`                 | Pointing device on the right side (Required - pick one only)          | _not defined_ |
+|`POINTING_DEVICE_COMBINED`              | Pointing device on both sides (Required - pick one only)              | _not defined_ |
+|`POINTING_DEVICE_ROTATION_90_RIGHT`     | (Optional) Rotates the X and Y data by  90 degrees.                   | _not defined_ |
+|`POINTING_DEVICE_ROTATION_180_RIGHT`    | (Optional) Rotates the X and Y data by 180 degrees.                   | _not defined_ |
+|`POINTING_DEVICE_ROTATION_270_RIGHT`    | (Optional) Rotates the X and Y data by 270 degrees.                   | _not defined_ |
+|`POINTING_DEVICE_INVERT_X_RIGHT`        | (Optional) Inverts the X axis report.                                 | _not defined_ |
+|`POINTING_DEVICE_INVERT_Y_RIGHT`        | (Optional) Inverts the Y axis report.                                 | _not defined_ |
+
+!> If there is a `_RIGHT` configuration option or callback, the [common configuration](feature_pointing_device.md?id=common-configuration) option will work for the left. For correct left/right detection you should setup a [handedness option](feature_split_keyboard?id=setting-handedness), `EE_HANDS` is usually a good option for an existing board that doesn't do handedness by hardware.
 
 
 ## Callbacks and Functions 
@@ -196,6 +216,21 @@ void           pointing_device_driver_set_cpi(uint16_t cpi) {}
 | `pointing_device_set_report(mouse_report)`                 | Sets the mouse report to the assigned `mouse_report_t` data structured passed to the function.                | 
 | `pointing_device_send(void)`                               | Sends the current mouse report to the host system.  Function can be replaced.                                 | 
 | `has_mouse_report_changed(old, new)`                       | Compares the old and new `mouse_report_t` data and returns true only if it has changed.                       |
+| `pointing_device_adjust_by_defines(mouse_report)`          | Applies rotations and invert configurations to a raw mouse report.                                             |
+
+
+## Split Keyboard Callbacks and Functions
+
+The combined functions below are only available when using `SPLIT_POINTING_ENABLE` and `POINTING_DEVICE_COMBINED`. The 2 callbacks `pointing_device_task_combined_*` replace the single sided equivalents above. See the [combined pointing devices example](feature_pointing_device.md?id=combined-pointing-devices)
+
+| Function                                                        | Description                                                                                                              |
+|-----------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------|
+| `pointing_device_set_shared_report(mouse_report)`               | Sets the shared mouse report to the assigned `mouse_report_t` data structured passed to the function.                    |
+| `pointing_device_set_cpi_on_side(bool, uint16_t)`               | Sets the CPI/DPI of one side, if supported. Passing `true` will set the left and `false` the right`                      |
+| `pointing_device_combine_reports(left_report, right_report)`    | Returns a combined mouse_report of left_report and right_report (as a `mouse_report_t` data structure)                   |
+| `pointing_device_task_combined_kb(left_report, right_report)`   | Callback, so keyboard code can intercept and modify the data. Returns a combined mouse report.                           |
+| `pointing_device_task_combined_user(left_report, right_report)` | Callback, so user code can intercept and modify. Returns a combined mouse report using `pointing_device_combine_reports` |
+| `pointing_device_adjust_by_defines_right(mouse_report)`         | Applies right side rotations and invert configurations to a raw mouse report.                                            |
 
 
 # Manipulating Mouse Reports
@@ -242,3 +277,62 @@ case MS_SPECIAL:
 ```
 
 Recall that the mouse report is set to zero (except the buttons) whenever it is sent, so the scrolling would only occur once in each case.
+
+## Split Examples
+
+The following examples make use the `SPLIT_POINTING_ENABLE` functionality and show how to manipulate the mouse report for a scrolling mode.
+
+### Single Pointing Device
+
+The following example will work with either `POINTING_DEVICE_LEFT` or `POINTING_DEVICE_RIGHT` and enables scrolling mode while on a particular layer.
+
+```c
+
+static bool scrolling_mode = false;
+
+layer_state_t layer_state_set_user(layer_state_t state) {
+    switch (get_highest_layer(state)) {
+        case _RAISE:  // If we're on the _RAISE layer enable scrolling mode
+            scrolling_mode = true;
+            pointing_device_set_cpi(2000);
+            break;
+        default:
+            if (scrolling_mode) {  // check if we were scrolling before and set disable if so
+                scrolling_mode = false;
+                pointing_device_set_cpi(8000);
+            }
+            break;
+    }
+    return state;
+}
+
+report_mouse_t pointing_device_task_user(report_mouse_t mouse_report) {
+    if (scrolling_mode) {
+        mouse_report.h = mouse_report.x;
+        mouse_report.v = mouse_report.y;
+        mouse_report.x = 0;
+        mouse_report.y = 0;
+    }
+    return mouse_report;
+}
+
+```
+
+### Combined Pointing Devices
+
+The following example requires `POINTING_DEVICE_COMBINED` and sets the left side pointing device to scroll only.
+
+```c
+void keyboard_post_init_user(void) {
+    pointing_device_set_cpi_on_side(true, 1000); //Set cpi on left side to a low value for slower scrolling.
+    pointing_device_set_cpi_on_side(false, 8000); //Set cpi on right side to a reasonable value for mousing.
+}
+
+report_mouse_t pointing_device_task_combined_user(report_mouse_t left_report, report_mouse_t right_report) {
+    left_report.h = left_report.x;
+    left_report.v = left_report.y;
+    left_report.x = 0;
+    left_report.y = 0;
+    return pointing_device_combine_reports(left_report, right_report);
+}
+```
diff --git a/docs/feature_split_keyboard.md b/docs/feature_split_keyboard.md
index c8ba18beeb..b51593308e 100644
--- a/docs/feature_split_keyboard.md
+++ b/docs/feature_split_keyboard.md
@@ -266,6 +266,14 @@ This enables transmitting the current OLED on/off status to the slave side of th
 
 This enables transmitting the current ST7565 on/off status to the slave side of the split keyboard. The purpose of this feature is to support state (on/off state only) syncing.
 
+```c
+#define SPLIT_POINTING_ENABLE
+```
+
+This enables transmitting the pointing device status to the master side of the split keyboard. The purpose of this feature is to enable use pointing devices on the slave side. 
+
+!> There is additional required configuration for `SPLIT_POINTING_ENABLE` outlined in the [pointing device documentation](feature_pointing_device.md?id=split-keyboard-configuration).
+
 ### Custom data sync between sides :id=custom-data-sync
 
 QMK's split transport allows for arbitrary data transactions at both the keyboard and user levels. This is modelled on a remote procedure call, with the master invoking a function on the slave side, with the ability to send data from master to slave, process it slave side, and send data back from slave to master.