Improve PS/2 mouse performance

[and3rson]

Source PR: #5408

Credits to @tomykaira for doing the actual work!

Description

This PR improves performance of PS/2 mouse in both interrupt mode and USART mode. On my keyboard, it reduces matrix scan delay from 11ms to 1ms. This makes it possible to use encoder AND trackpoint at the same time without any lags!

Additional changes introduced are:

• Compatibility with USART mode: platforms/avr/drivers/ps2/ps2_usart.c:76
• Call ps2_mouse_set_stream_mode during initialization if stream mode is selected - not sure why that wasn't done already: drivers/ps2/ps2_mouse.c:56. This makes USART mode work properly when booting the keyboard.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

• PS2_MOUSE_ENABLE ridiculously slows down matrix scan rate #5357
• Avoid READ command in stream mode #5408

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

Test case

Wiring & trackpoint images (source: https://github.com/joric/jorne/wiki/Trackpoint)

Config (tested with both INT & USARG modes)

#define PS2_MOUSE_INIT_DELAY 200

#ifdef PS2_USE_USART
#define PS2_CLOCK_PIN   D5
#define PS2_DATA_PIN    D2

/* #define PS2_MOUSE_USE_REMOTE_MODE */

/* 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

#ifdef PS2_USE_INT
// Note: pins are swapped, so re-soldering is needed to test both modes
#define PS2_CLOCK_PIN   D2
#define PS2_DATA_PIN    D5

/* #define PS2_MOUSE_USE_REMOTE_MODE */

#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
#endif

Demo of me using trackpoint & encoder simultaneously: https://imgur.com/a/cqL8j1x