arch/x86/core/cpuhalt.c

/*
 * Copyright (c) 2011-2015 Wind River Systems, Inc.
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr.h>
#include <debug/tracing.h>
#include <arch/cpu.h>

/**
 *
 * @brief Power save idle routine
 *
 * This function will be called by the kernel idle loop or possibly within
 * an implementation of _sys_power_save_idle in the kernel when the
 * '_sys_power_save_flag' variable is non-zero.  The 'hlt' instruction
 * will be issued causing a low-power consumption sleep mode.
 *
 * @return N/A
 */
void k_cpu_idle(void)
{
	z_sys_trace_idle();
#if defined(CONFIG_BOOT_TIME_MEASUREMENT)
	__idle_time_stamp = k_cycle_get_32();
#endif

	__asm__ volatile (
	    "sti\n\t"
	    "hlt\n\t");
}

/**
 *
 * @brief Atomically re-enable interrupts and enter low power mode
 *
 * INTERNAL
 * The requirements for k_cpu_atomic_idle() are as follows:
 * 1) The enablement of interrupts and entering a low-power mode needs to be
 *    atomic, i.e. there should be no period of time where interrupts are
 *    enabled before the processor enters a low-power mode.  See the comments
 *    in k_lifo_get(), for example, of the race condition that
 *    occurs if this requirement is not met.
 *
 * 2) After waking up from the low-power mode, the interrupt lockout state
 *    must be restored as indicated in the 'key' input parameter.
 *
 * @return N/A
 */

void k_cpu_atomic_idle(unsigned int key)
{
	z_sys_trace_idle();

	__asm__ volatile (
	    "sti\n\t"
	    /*
	     * The following statement appears in "Intel 64 and IA-32
	     * Architectures Software Developer's Manual", regarding the 'sti'
	     * instruction:
	     *
	     * "After the IF flag is set, the processor begins responding to
	     *    external, maskable interrupts after the next instruction is
	     *    executed."
	     *
	     * Thus the IA-32 implementation of k_cpu_atomic_idle() will
	     * atomically re-enable interrupts and enter a low-power mode.
	     */
	    "hlt\n\t");

	/* restore interrupt lockout state before returning to caller */
	if ((key & 0x200U) == 0U) {
		__asm__ volatile("cli");
	}
}