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+## PS/2 Mouse Support
+
+Its possible to hook up a PS/2 mouse (for example touchpads or trackpoints) to your keyboard as a composite device.
+
+To hook up a Trackpoint, you need to obtain a Trackpoint module (i.e. harvest from a Thinkpad keyboard), identify the function of each pin of the module, and make the necessary circuitry between controller and Trackpoint module. For more information, please refer to [Trackpoint Hardware](https://deskthority.net/wiki/TrackPoint_Hardware) page on Deskthority Wiki.
+
+There are three available modes for hooking up PS/2 devices: USART (best), interrupts (better) or busywait (not recommended).
+
+### Busywait version
+
+Note: This is not recommended, you may encounter jerky movement or unsent inputs. Please use interrupt or USART version if possible.
+
+In rules.mk:
+
+```
+PS2_MOUSE_ENABLE = yes
+PS2_USE_BUSYWAIT = yes
+```
+
+In your keyboard config.h:
+
+```
+#ifdef PS2_USE_BUSYWAIT
+#   define PS2_CLOCK_PORT  PORTD
+#   define PS2_CLOCK_PIN   PIND
+#   define PS2_CLOCK_DDR   DDRD
+#   define PS2_CLOCK_BIT   1
+#   define PS2_DATA_PORT   PORTD
+#   define PS2_DATA_PIN    PIND
+#   define PS2_DATA_DDR    DDRD
+#   define PS2_DATA_BIT    2
+#endif
+```
+
+### Interrupt version
+
+The following example uses D2 for clock and D5 for data. You can use any INT or PCINT pin for clock, and any pin for data.
+
+In rules.mk:
+
+```
+PS2_MOUSE_ENABLE = yes
+PS2_USE_INT = yes
+```
+
+In your keyboard config.h:
+
+```
+#ifdef PS2_USE_INT
+#define PS2_CLOCK_PORT  PORTD
+#define PS2_CLOCK_PIN   PIND
+#define PS2_CLOCK_DDR   DDRD
+#define PS2_CLOCK_BIT   2
+#define PS2_DATA_PORT   PORTD
+#define PS2_DATA_PIN    PIND
+#define PS2_DATA_DDR    DDRD
+#define PS2_DATA_BIT    5
+
+#define PS2_INT_INIT()  do {    \
+    EICRA |= ((1<<ISC21) |      \
+              (0<<ISC20));      \
+} while (0)
+#define PS2_INT_ON()  do {      \
+    EIMSK |= (1<<INT2);         \
+} while (0)
+#define PS2_INT_OFF() do {      \
+    EIMSK &= ~(1<<INT2);        \
+} while (0)
+#define PS2_INT_VECT   INT2_vect
+#endif
+```
+
+### USART version
+
+To use USART on the ATMega32u4, you have to use PD5 for clock and PD2 for data. If one of those are unavailable, you need to use interrupt version.
+
+In rules.mk:
+
+```
+PS2_MOUSE_ENABLE = yes
+PS2_USE_USART = yes
+```
+
+In your keyboard config.h:
+
+```
+#ifdef PS2_USE_USART
+#define PS2_CLOCK_PORT  PORTD
+#define PS2_CLOCK_PIN   PIND
+#define PS2_CLOCK_DDR   DDRD
+#define PS2_CLOCK_BIT   5
+#define PS2_DATA_PORT   PORTD
+#define PS2_DATA_PIN    PIND
+#define PS2_DATA_DDR    DDRD
+#define PS2_DATA_BIT    2
+
+/* synchronous, odd parity, 1-bit stop, 8-bit data, sample at falling edge */
+/* set DDR of CLOCK as input to be slave */
+#define PS2_USART_INIT() do {   \
+    PS2_CLOCK_DDR &= ~(1<<PS2_CLOCK_BIT);   \
+    PS2_DATA_DDR &= ~(1<<PS2_DATA_BIT);     \
+    UCSR1C = ((1 << UMSEL10) |  \
+              (3 << UPM10)   |  \
+              (0 << USBS1)   |  \
+              (3 << UCSZ10)  |  \
+              (0 << UCPOL1));   \
+    UCSR1A = 0;                 \
+    UBRR1H = 0;                 \
+    UBRR1L = 0;                 \
+} while (0)
+#define PS2_USART_RX_INT_ON() do {  \
+    UCSR1B = ((1 << RXCIE1) |       \
+              (1 << RXEN1));        \
+} while (0)
+#define PS2_USART_RX_POLL_ON() do { \
+    UCSR1B = (1 << RXEN1);          \
+} while (0)
+#define PS2_USART_OFF() do {    \
+    UCSR1C = 0;                 \
+    UCSR1B &= ~((1 << RXEN1) |  \
+                (1 << TXEN1));  \
+} while (0)
+#define PS2_USART_RX_READY      (UCSR1A & (1<<RXC1))
+#define PS2_USART_RX_DATA       UDR1
+#define PS2_USART_ERROR         (UCSR1A & ((1<<FE1) | (1<<DOR1) | (1<<UPE1)))
+#define PS2_USART_RX_VECT       USART1_RX_vect
+#endif
+```
+
+### Additional Settings
+
+#### PS/2 mouse features
+
+These enable settings supported by the PS/2 mouse protocol: http://www.computer-engineering.org/ps2mouse/
+
+```
+/* Use remote mode instead of the default stream mode (see link) */
+#define PS2_MOUSE_USE_REMOTE_MODE  
+
+/* Enable the scrollwheel or scroll gesture on your mouse or touchpad */
+#define PS2_MOUSE_ENABLE_SCROLLING
+
+/* Some mice will need a scroll mask to be configured. The default is 0xFF. */
+#define PS2_MOUSE_SCROLL_MASK 0x0F
+
+/* Applies a transformation to the movement before sending to the host (see link) */
+#define PS2_MOUSE_USE_2_1_SCALING
+
+/* The time to wait after initializing the ps2 host */
+#define PS2_MOUSE_INIT_DELAY 1000 /* Default */
+```
+
+You can also call the following functions from ps2_mouse.h
+
+```
+void ps2_mouse_disable_data_reporting(void);
+
+void ps2_mouse_enable_data_reporting(void);
+
+void ps2_mouse_set_remote_mode(void);
+
+void ps2_mouse_set_stream_mode(void);
+
+void ps2_mouse_set_scaling_2_1(void);
+
+void ps2_mouse_set_scaling_1_1(void);
+
+void ps2_mouse_set_resolution(ps2_mouse_resolution_t resolution);
+
+void ps2_mouse_set_sample_rate(ps2_mouse_sample_rate_t sample_rate);
+```
+
+#### Fine control
+
+Use the following defines to change the sensitivity and speed of the mouse.
+Note: you can also use `ps2_mouse_set_resolution` for the same effect (not supported on most touchpads).
+
+```
+#define PS2_MOUSE_X_MULTIPLIER 3
+#define PS2_MOUSE_Y_MULTIPLIER 3
+#define PS2_MOUSE_V_MULTIPLIER 1
+```
+
+#### Scroll button
+
+If you're using a trackpoint, you will likely want to be able to use it for scrolling.
+Its possible to enable a "scroll button/s" that when pressed will cause the mouse to scroll instead of moving.
+To enable the feature, you must set a scroll button mask as follows:
+
+```
+#define PS2_MOUSE_SCROLL_BTN_MASK (1<<PS2_MOUSE_BUTTON_MIDDLE) /* Default */
+```
+
+To disable the scroll button feature:
+
+```
+#define PS2_MOUSE_SCROLL_BTN_MASK 0
+```
+
+The available buttons are:
+
+```
+#define PS2_MOUSE_BTN_LEFT      0
+#define PS2_MOUSE_BTN_RIGHT     1
+#define PS2_MOUSE_BTN_MIDDLE    2
+```
+
+You can also combine buttons in the mask by `|`ing them together.
+
+Once you've configured your scroll button mask, you must configure the scroll button send interval.
+This is the interval before which if the scroll buttons were released they would be sent to the host.
+After this interval, they will cause the mouse to scroll and will not be sent.
+
+```
+#define PS2_MOUSE_SCROLL_BTN_SEND 300 /* Default */
+```
+
+To disable sending the scroll buttons:
+```
+#define PS2_MOUSE_SCROLL_BTN_SEND 0
+```
+
+Fine control over the scrolling is supported with the following defines:
+
+```
+#define PS2_MOUSE_SCROLL_DIVISOR_H 2
+#define PS2_MOUSE_SCROLL_DIVISOR_V 2
+```
+
+#### Debug settings
+
+To debug the mouse, add `debug_mouse = true` or enable via bootmagic.
+
+```
+/* To debug the mouse reports */
+#define PS2_MOUSE_DEBUG_HID
+#define PS2_MOUSE_DEBUG_RAW
+```