nt-lite/code/hal/hal_mouse.c

// hal_mouse.c - PS/2 auxiliary mouse driver
//
// Sits on IRQ 12, sharing the 8042 controller with the keyboard (IRQ 1).
// hal_keyboard.c has already issued command 0xA8 (enable aux port) by the
// time HalMouseInitialize is called, so we only need to:
//   1. Enable aux interrupts in the 8042 command byte (bit 1, clears bit 5).
//   2. Send the standard mouse init sequence (reset → defaults → enable).
//   3. Wire up the ISR and expose the HAL_MOUSE vtable.
//
// Packet format - standard 3-byte PS/2 mouse (no scroll wheel):
//   Byte 0:  [YOV][XOV][YS][XS][1][M][R][L]
//   Byte 1:  delta-X unsigned magnitude (sign in byte-0 bit 4)
//   Byte 2:  delta-Y unsigned magnitude (sign in byte-0 bit 5); PS/2 Y+ = up
//
// The ISR accumulates the 3-byte packet, converts it to a screen-space delta
// (Y-axis flipped), clamps the absolute position to [0, bounds), enqueues a
// MOUSE_EVENT, and then calls EraseOldCursor / DrawNewCursor via the two
// screen helpers that hal_screen.c exports.
//
// Threading model
// ---------------
//   Single-producer (ISR on IRQ 12) / single-consumer ring buffer.
//   All ISR-written fields are volatile; on a uniprocessor this is sufficient.
//   On SMP, add acquire/release barriers around gHead / gTail.

#include <stdint.h>
#include <stdbool.h>
#include <intrin.h>
#include <hal_api.h>

// -- PS/2 port addresses -------------------------------------------------------
#define PS2_DATA  0x60u
#define PS2_STAT  0x64u
#define PS2_CMD   0x64u

// -- Ring buffer ---------------------------------------------------------------
#define MOUSE_BUF_SIZE  64u
#define MOUSE_BUF_MASK  (MOUSE_BUF_SIZE - 1u)

typedef struct {
    int     dx, dy;
    uint8_t buttons;    // bit0=left, bit1=right, bit2=middle
} MOUSE_EVENT;

static MOUSE_EVENT  gBuf[MOUSE_BUF_SIZE];
static volatile int gHead = 0;   // consumer read pointer
static volatile int gTail = 0;   // producer write pointer (updated by ISR)

// -- Absolute cursor position & screen bounds ----------------------------------
static volatile int gMouseX  = 0;
static volatile int gMouseY  = 0;
static volatile int gBoundsW = 1920;
static volatile int gBoundsH = 1080;

// -- 3-byte packet assembly ----------------------------------------------------
static volatile uint8_t gPacket[3];
static volatile int     gPacketIdx = 0;   // 0, 1, or 2

// -- Optional callback (called from ISR) ---------------------------------------
static void (* volatile gCallback)(int dx, int dy, uint8_t buttons) = NULL;

// -- Cursor helpers provided by hal_screen.c -----------------------------------
// Declared here; defined in hal_screen.c.
extern void HalScreenDrawCursor(int x, int y);
extern void HalScreenEraseCursor(void);

// -- 8042 low-level helpers ----------------------------------------------------
// Wait until the 8042's input buffer is empty (bit 1 of status = 0) so we
// can safely write to PS2_DATA or PS2_CMD.
static void Ps2WaitInput(void) {
    int timeout = 100000;
    while ((__inbyte(PS2_STAT) & 0x02u) && --timeout) { /* spin */ }
}

// Wait until the 8042's output buffer has data (bit 0 of status = 1).
static void Ps2WaitOutput(void) {
    int timeout = 100000;
    while (!(__inbyte(PS2_STAT) & 0x01u) && --timeout) { /* spin */ }
}

// Route the next write to the auxiliary (mouse) device rather than the keyboard.
static void MouseSendByte(uint8_t byte) {
    Ps2WaitInput();
    __outbyte(PS2_CMD, 0xD4u);   // "write to mouse" prefix
    Ps2WaitInput();
    __outbyte(PS2_DATA, byte);
}

// Read one byte from the PS/2 output buffer (shared by keyboard and mouse).
static uint8_t MouseRecvByte(void) {
    Ps2WaitOutput();
    return __inbyte(PS2_DATA);
}

// -- Interrupt service routine --------------------------------------------------
// Called with interrupts disabled by KeIrqDispatch (IRQ 12).
// The dispatcher sends the APIC EOI before this function is invoked.
static void MouseIsr(void) {
    uint8_t data = __inbyte(PS2_DATA);

    // Synchronisation guard: the first byte of every packet has bit 3 set.
    // If we lose sync, wait for the next valid first byte before assembling.
    if (gPacketIdx == 0) {
        if (!(data & 0x08u)) return;   // not a valid first byte - discard
    }

    gPacket[gPacketIdx++] = data;
    if (gPacketIdx < 3) return;        // packet not yet complete
    gPacketIdx = 0;

    // -- Decode flags ----------------------------------------------------------
    uint8_t flags   = gPacket[0];

    // Overflow bits: if either is set the movement data is meaningless.
    if (flags & 0xC0u) return;

    uint8_t buttons = flags & 0x07u;

    // Convert unsigned magnitudes + sign bits to signed 9-bit values.
    int dx = (int)gPacket[1] - ((flags & 0x10u) ? 256 : 0);
    int dy = (int)gPacket[2] - ((flags & 0x20u) ? 256 : 0);
    dy = -dy;   // PS/2 Y+ = up; screen Y+ = down, so invert.

    // -- Update absolute position (clamped to screen bounds) ------------------
    HalScreenEraseCursor();

    int nx = gMouseX + dx;
    int ny = gMouseY + dy;
    if (nx < 0)             nx = 0;
    if (nx >= gBoundsW)     nx = gBoundsW - 1;
    if (ny < 0)             ny = 0;
    if (ny >= gBoundsH)     ny = gBoundsH - 1;
    gMouseX = nx;
    gMouseY = ny;

    HalScreenDrawCursor(nx, ny);

    // -- Enqueue event; silently drop if buffer is full -----------------------
    int next = (gTail + 1) & (int)MOUSE_BUF_MASK;
    if (next != gHead) {
        gBuf[gTail].dx      = dx;
        gBuf[gTail].dy      = dy;
        gBuf[gTail].buttons = buttons;
        gTail               = next;
    }

    // -- Optional callback (raw ISR context) -----------------------------------
    void (*cb)(int, int, uint8_t) = (void (*)(int, int, uint8_t))gCallback;
    if (cb) cb(dx, dy, buttons);
}

// -- Consumer API --------------------------------------------------------------
static bool MousePoll(void) {
    return gHead != gTail;
}

static bool MouseRead(int* dx, int* dy, uint8_t* buttons) {
    if (gHead == gTail) return false;
    *dx      = gBuf[gHead].dx;
    *dy      = gBuf[gHead].dy;
    *buttons = gBuf[gHead].buttons;
    gHead    = (gHead + 1) & (int)MOUSE_BUF_MASK;
    return true;
}

static void MouseGetPosition(int* x, int* y) {
    *x = gMouseX;
    *y = gMouseY;
}

static void MouseSetPosition(int x, int y) {
    gMouseX = x;
    gMouseY = y;
}

static void MouseSetBounds(int w, int h) {
    gBoundsW = w;
    gBoundsH = h;
}

static void MouseSetCallback(void (*cb)(int dx, int dy, uint8_t buttons)) {
    gCallback = cb;
}

// -- Initializer ---------------------------------------------------------------
// Called from HalInitialize in hal_main.c after the screen is ready.
// hal_keyboard.c has already sent 0xA8 (enable aux port) to port 0x64.
void HalMouseInitialize(HAL_MOUSE* out, int screenW, int screenH) {
    gBoundsW = screenW;
    gBoundsH = screenH;
    gMouseX  = screenW / 2;
    gMouseY  = screenH / 2;

    // -----------------------------------------------------------------
    // Step 1: Enable aux interrupts in the 8042 command byte.
    //   - Bit 1 (0x02): enable auxiliary interrupt (drives IRQ 12).
    //   - Bit 5 (0x20): disables the aux clock when set; clear it.
    // -----------------------------------------------------------------
    Ps2WaitInput();
    __outbyte(PS2_CMD, 0x20u);   // read current command byte
    Ps2WaitOutput();
    uint8_t cmd = __inbyte(PS2_DATA);
    cmd |=  0x02u;               // enable aux interrupt
    cmd &= ~0x20u;               // clear "disable aux clock"
    Ps2WaitInput();
    __outbyte(PS2_CMD, 0x60u);   // write command byte
    Ps2WaitInput();
    __outbyte(PS2_DATA, cmd);

    // -----------------------------------------------------------------
    // Step 2: Reset mouse (0xFF).
    //   Mouse replies: ACK (0xFA), self-test pass (0xAA), ID (0x00).
    // -----------------------------------------------------------------
    MouseSendByte(0xFFu);        // reset
    MouseRecvByte();             // 0xFA  - ACK
    MouseRecvByte();             // 0xAA  - BAT passed
    MouseRecvByte();             // 0x00  - device ID

    // -----------------------------------------------------------------
    // Step 3: Set default parameters (sampling rate 100, 4 counts/mm).
    //   Mouse replies: ACK.
    // -----------------------------------------------------------------
    MouseSendByte(0xF6u);        // set defaults
    MouseRecvByte();             // ACK

    // -----------------------------------------------------------------
    // Step 4: Enable data reporting.
    //   Mouse will now send 3-byte packets on every movement/button event.
    // -----------------------------------------------------------------
    MouseSendByte(0xF4u);        // enable data reporting
    MouseRecvByte();             // ACK

    // Draw the initial cursor at the centre of the screen.
    HalScreenDrawCursor(gMouseX, gMouseY);

    // Populate vtable.
    out->Poll        = MousePoll;
    out->Read        = MouseRead;
    out->SetCallback = MouseSetCallback;
    out->GetPosition = MouseGetPosition;
    out->SetPosition = MouseSetPosition;
    out->SetBounds   = MouseSetBounds;
    out->Isr         = MouseIsr;
    out->IrqNumber   = 12;
}