apic_timer.c

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/* SPDX-License-Identifier: GPL-2.0-only */
 
#include <stdint.h>
#include <console/console.h>
#include <delay.h>
#include <thread.h>
#include <cpu/x86/lapic.h>
 
void init_timer(void)
{
        /* Set the APIC timer to no interrupts and periodic mode */
        lapic_write(LAPIC_LVTT, (LAPIC_LVT_TIMER_PERIODIC | LAPIC_LVT_MASKED));
 
        /* Set the divider to 1, no divider */
        lapic_write(LAPIC_TDCR, LAPIC_TDR_DIV_1);
 
        /* Set the initial counter to 0xffffffff */
        lapic_write(LAPIC_TMICT, 0xffffffff);
}
 
void udelay(u32 usecs)
{
        u32 start, value, ticks, timer_fsb;
 
        if (!thread_yield_microseconds(usecs))
                return;
 
        timer_fsb = get_timer_fsb();
        if (!timer_fsb || (lapic_read(LAPIC_LVTT) &
                (LAPIC_LVT_TIMER_PERIODIC | LAPIC_LVT_MASKED)) !=
                (LAPIC_LVT_TIMER_PERIODIC | LAPIC_LVT_MASKED)) {
                init_timer();
                timer_fsb = get_timer_fsb();
        }
 
        /* Calculate the number of ticks to run, our FSB runs at timer_fsb Mhz
         */
        ticks = usecs * timer_fsb;
        start = lapic_read(LAPIC_TMCCT);
        do {
                value = lapic_read(LAPIC_TMCCT);
        } while ((start - value) < ticks);
}
 
#if CONFIG(LAPIC_MONOTONIC_TIMER)
#include <timer.h>
 
static struct monotonic_counter {
        int initialized;
        struct mono_time time;
        uint32_t last_value;
} mono_counter;
 
void timer_monotonic_get(struct mono_time *mt)
{
        uint32_t current_tick;
        uint32_t usecs_elapsed;
        uint32_t timer_fsb;
 
        if (!mono_counter.initialized) {
                init_timer();
                timer_fsb = get_timer_fsb();
                /* An FSB frequency of 200Mhz provides a 20 second polling
                 * interval between timer_monotonic_get() calls before wrap
                 * around occurs. */
                if (timer_fsb > 200)
                        printk(BIOS_WARNING,
                               "apic timer freq (%d) may be too fast.\n",
                               timer_fsb);
                mono_counter.last_value = lapic_read(LAPIC_TMCCT);
                mono_counter.initialized = 1;
        }
 
        timer_fsb = get_timer_fsb();
        current_tick = lapic_read(LAPIC_TMCCT);
        /* Note that the APIC timer counts down. */
        usecs_elapsed = (mono_counter.last_value - current_tick) / timer_fsb;
 
        /* Update current time and tick values only if a full tick occurred. */
        if (usecs_elapsed) {
                mono_time_add_usecs(&mono_counter.time, usecs_elapsed);
                mono_counter.last_value = current_tick;
        }
 
        /* Save result. */
        *mt = mono_counter.time;
}
#endif