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/*
* This file is part of the coreboot project.
*
* Copyright (C) 2013 Google, Inc.
*
* 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; version 2 of the License.
*
* 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, write to the Free Software
* Foundation, Inc.
*/
#include <stdint.h>
#include <cpu/x86/msr.h>
#include <timer.h>
#define MSR_COUNTER_24_MHz 0x637
static struct monotonic_counter {
int initialized;
struct mono_time time;
uint32_t last_value;
} mono_counter;
static inline uint32_t read_counter_msr(void)
{
/* Even though the MSR is 64-bit it is assumed that the hardware
* is polled frequently enough to only use the lower 32-bits. */
msr_t counter_msr;
counter_msr = rdmsr(MSR_COUNTER_24_MHz);
return counter_msr.lo;
}
void timer_monotonic_get(struct mono_time *mt)
{
uint32_t current_tick;
uint32_t usecs_elapsed;
if (!mono_counter.initialized) {
mono_counter.last_value = read_counter_msr();
mono_counter.initialized = 1;
}
current_tick = read_counter_msr();
usecs_elapsed = (current_tick - mono_counter.last_value) / 24;
/* 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;
}
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