LAPIC Timer - 2 Ways: Periodic and Oneshot mode

apic.c

/*
	This file is extracted from a modern x86_64 UNIX-like microkernel-based
	operating system which is called apoptOS
	Everything is openly developed on GitHub: https://github.com/Tix3Dev/apoptOS

	Copyright (C) 2022  Yves Vollmeier <https://github.com/Tix3Dev>
	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.
	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.
	You should have received a copy of the GNU General Public License
	along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

#define LAPIC_ID_REG		0x020
#define LAPIC_EOI_REG		0x0B0
#define LAPIC_SPURIOUS_REG	0x0F0
#define LAPIC_ICR0_REG		0x300
#define LAPIC_ICR1_REG		0x310
#define LAPIC_TIMER_REG		0x320
#define LAPIC_TIMER_INITCNT_REG	0x380
#define LAPIC_TIMER_CURCNT_REG	0x390
#define LAPIC_TIMER_DIV_REG	0x3E0

#define LAPIC_ENABLE_BIT	(1 << 8)
#define LAPIC_TIMER_DISABLE_BIT	(1 << 16)

#define LAPIC_TIMER_PERIODIC_MODE 0x20000

#define US_TIMESLICE_PERIOD 5000

#define LAPIC_TIMER_INT	32


/* 1 Way: Periodic mode */


// unmask timer pin and start periodic LAPIC timer (with specified period)
void lapic_timer_init(void)
{
    uint32_t period = lapic_timer_calibrate(US_TIMESLICE_PERIOD);

    lapic_write_reg(LAPIC_TIMER_REG, LAPIC_TIMER_INT | LAPIC_TIMER_PERIODIC_MODE);
    lapic_write_reg(LAPIC_TIMER_DIV_REG, 0x3);
    lapic_write_reg(LAPIC_TIMER_INITCNT_REG, period);
    
    log(INFO, "LAPIC timer initialized - Firing IRQ's from now on\n");
}

// return how many ticks it took the LAPIC timer for the specified amount of microseconds
uint32_t lapic_timer_calibrate(uint32_t us)
{
    lapic_write_reg(LAPIC_TIMER_DIV_REG, 0x3);

    uint32_t initial_count = 0xFFFFFFFF;
    lapic_write_reg(LAPIC_TIMER_INITCNT_REG, initial_count);

    hpet_usleep(us);

    lapic_write_reg(LAPIC_TIMER_REG, LAPIC_TIMER_DISABLE_BIT);
    uint32_t final_count = lapic_read_reg(LAPIC_TIMER_CURCNT_REG);

    uint32_t total_ticks = initial_count - final_count;
    return total_ticks;
}

lapic_timer_init();


/* 2 Way: Oneshot mode */


static uint32_t lapic_timer_freq = 0;

// globally set the lapic timer frequency through calibration
void lapic_timer_init(void)
{
    // frequency = ticks per second -> calibrate 1ms -> multiply by 1000 to get one second
    lapic_timer_freq = lapic_timer_calibrate(1000) * 1000;

    log(INFO, "LAPIC timer initialized - Oneshot's possible from now on\n");
}

// return how many ticks it took the LAPIC timer for the specified amount of microseconds
uint32_t lapic_timer_calibrate(uint32_t us)
{
    lapic_write_reg(LAPIC_TIMER_DIV_REG, 3);

    uint32_t initial_count = 0xFFFFFFFF;
    lapic_write_reg(LAPIC_TIMER_INITCNT_REG, initial_count);

    hpet_usleep(us);

    lapic_write_reg(LAPIC_TIMER_REG, LAPIC_TIMER_DISABLE_BIT);
    uint32_t final_count = lapic_read_reg(LAPIC_TIMER_CURCNT_REG);

    uint32_t total_ticks = initial_count - final_count;
    return total_ticks;
}

// send an interrupt vector (through the LVT and not IOAPIC redirection table) after
// the specified amount of microseconds, where interrupt vector = LAPIC_TIMER_INT
void lapic_timer_oneshot(uint32_t us)
{
    uint32_t ticks = us * (lapic_timer_freq / 1000000);

    lapic_write_reg(LAPIC_TIMER_REG, LAPIC_TIMER_INT);
    lapic_write_reg(LAPIC_TIMER_DIV_REG, 3);
    lapic_write_reg(LAPIC_TIMER_INITCNT_REG, ticks);
}

lapic_timer_init();

// if desired, e.g. to wait 5 seconds:
// lapic_timer_oneshot(5 * 1000 * 1000);