xv6/lapic.c

// The local APIC manages internal (non-I/O) interrupts.
// See Chapter 8 & Appendix C of Intel processor manual volume 3.

#include "param.h"
#include "types.h"
#include "defs.h"
#include "date.h"
#include "memlayout.h"
#include "traps.h"
#include "mmu.h"
#include "x86.h"

// Local APIC registers, divided by 4 for use as uint[] indices.
#define ID      (0x0020 / 4)   // ID
#define VER     (0x0030 / 4)   // Version
#define TPR     (0x0080 / 4)   // Task Priority
#define EOI     (0x00B0 / 4)   // EOI
#define SVR     (0x00F0 / 4)   // Spurious Interrupt Vector
  #define ENABLE     0x00000100   // Unit Enable
#define ESR     (0x0280 / 4)   // Error Status
#define ICRLO   (0x0300 / 4)   // Interrupt Command
  #define INIT       0x00000500   // INIT/RESET
  #define STARTUP    0x00000600   // Startup IPI
  #define DELIVS     0x00001000   // Delivery status
  #define ASSERT     0x00004000   // Assert interrupt (vs deassert)
  #define DEASSERT   0x00000000
  #define LEVEL      0x00008000   // Level triggered
  #define BCAST      0x00080000   // Send to all APICs, including self.
  #define BUSY       0x00001000
  #define FIXED      0x00000000
#define ICRHI   (0x0310 / 4)   // Interrupt Command [63:32]
#define TIMER   (0x0320 / 4)   // Local Vector Table 0 (TIMER)
  #define X1         0x0000000B   // divide counts by 1
  #define PERIODIC   0x00020000   // Periodic
#define PCINT   (0x0340 / 4)   // Performance Counter LVT
#define LINT0   (0x0350 / 4)   // Local Vector Table 1 (LINT0)
#define LINT1   (0x0360 / 4)   // Local Vector Table 2 (LINT1)
#define ERROR   (0x0370 / 4)   // Local Vector Table 3 (ERROR)
  #define MASKED     0x00010000   // Interrupt masked
#define TICR    (0x0380 / 4)   // Timer Initial Count
#define TCCR    (0x0390 / 4)   // Timer Current Count
#define TDCR    (0x03E0 / 4)   // Timer Divide Configuration

volatile uint *lapic;  // Initialized in mp.c


static void lapicw(int index, int value) {
    lapic[index] = value;
    lapic[ID];  // wait for write to finish, by reading
}

void lapicinit(void) {
    if (!lapic) {
        return;
    }

    // Enable local APIC; set spurious interrupt vector.
    lapicw(SVR, ENABLE | (T_IRQ0 + IRQ_SPURIOUS));

    // The timer repeatedly counts down at bus frequency
    // from lapic[TICR] and then issues an interrupt.
    // If xv6 cared more about precise timekeeping,
    // TICR would be calibrated using an external time source.
    lapicw(TDCR, X1);
    lapicw(TIMER, PERIODIC | (T_IRQ0 + IRQ_TIMER));
    lapicw(TICR, 10000000);

    // Disable logical interrupt lines.
    lapicw(LINT0, MASKED);
    lapicw(LINT1, MASKED);

    // Disable performance counter overflow interrupts
    // on machines that provide that interrupt entry.
    if (((lapic[VER] >> 16) & 0xFF) >= 4) {
        lapicw(PCINT, MASKED);
    }

    // Map error interrupt to IRQ_ERROR.
    lapicw(ERROR, T_IRQ0 + IRQ_ERROR);

    // Clear error status register (requires back-to-back writes).
    lapicw(ESR, 0);
    lapicw(ESR, 0);

    // Ack any outstanding interrupts.
    lapicw(EOI, 0);

    // Send an Init Level De-Assert to synchronise arbitration ID's.
    lapicw(ICRHI, 0);
    lapicw(ICRLO, BCAST | INIT | LEVEL);
    while (lapic[ICRLO] & DELIVS) {
        ;
    }

    // Enable interrupts on the APIC (but not on the processor).
    lapicw(TPR, 0);
}

int lapicid(void) {
    if (!lapic) {
        return 0;
    }
    return lapic[ID] >> 24;
}

// Acknowledge interrupt.
void lapiceoi(void) {
    if (lapic) {
        lapicw(EOI, 0);
    }
}

// Spin for a given number of microseconds.
// On real hardware would want to tune this dynamically.
void microdelay(int us) {
}

#define CMOS_PORT    0x70
#define CMOS_RETURN  0x71

// Start additional processor running entry code at addr.
// See Appendix B of MultiProcessor Specification.
void lapicstartap(uchar apicid, uint addr)      {
    int i;
    ushort *wrv;

    // "The BSP must initialize CMOS shutdown code to 0AH
    // and the warm reset vector (DWORD based at 40:67) to point at
    // the AP startup code prior to the [universal startup algorithm]."
    outb(CMOS_PORT, 0xF);  // offset 0xF is shutdown code
    outb(CMOS_PORT + 1, 0x0A);
    wrv = (ushort*)P2V((0x40 << 4 | 0x67));  // Warm reset vector
    wrv[0] = 0;
    wrv[1] = addr >> 4;

    // "Universal startup algorithm."
    // Send INIT (level-triggered) interrupt to reset other CPU.
    lapicw(ICRHI, apicid << 24);
    lapicw(ICRLO, INIT | LEVEL | ASSERT);
    microdelay(200);
    lapicw(ICRLO, INIT | LEVEL);
    microdelay(100);    // should be 10ms, but too slow in Bochs!

    // Send startup IPI (twice!) to enter code.
    // Regular hardware is supposed to only accept a STARTUP
    // when it is in the halted state due to an INIT.  So the second
    // should be ignored, but it is part of the official Intel algorithm.
    // Bochs complains about the second one.  Too bad for Bochs.
    for (i = 0; i < 2; i++) {
        lapicw(ICRHI, apicid << 24);
        lapicw(ICRLO, STARTUP | (addr >> 12));
        microdelay(200);
    }
}

#define CMOS_STATA   0x0a
#define CMOS_STATB   0x0b
#define CMOS_UIP    (1 << 7)        // RTC update in progress

#define SECS    0x00
#define MINS    0x02
#define HOURS   0x04
#define DAY     0x07
#define MONTH   0x08
#define YEAR    0x09

static uint cmos_read(uint reg) {
    outb(CMOS_PORT,  reg);
    microdelay(200);

    return inb(CMOS_RETURN);
}

static void fill_rtcdate(struct rtcdate *r) {
    r->second = cmos_read(SECS);
    r->minute = cmos_read(MINS);
    r->hour   = cmos_read(HOURS);
    r->day    = cmos_read(DAY);
    r->month  = cmos_read(MONTH);
    r->year   = cmos_read(YEAR);
}

// qemu seems to use 24-hour GWT and the values are BCD encoded
void cmostime(struct rtcdate *r) {
    struct rtcdate t1, t2;
    int sb, bcd;

    sb = cmos_read(CMOS_STATB);

    bcd = (sb & (1 << 2)) == 0;

    // make sure CMOS doesn't modify time while we read it
    for (;;) {
        fill_rtcdate(&t1);
        if (cmos_read(CMOS_STATA) & CMOS_UIP) {
            continue;
        }
        fill_rtcdate(&t2);
        if (memcmp(&t1, &t2, sizeof(t1)) == 0) {
            break;
        }
    }

    // convert
    if (bcd) {
#define    CONV(x)     (t1.x = ((t1.x >> 4) * 10) + (t1.x & 0xf))
        CONV(second);
        CONV(minute);
        CONV(hour  );
        CONV(day   );
        CONV(month );
        CONV(year  );
#undef     CONV
    }

    *r = t1;
    r->year += 2000;
}