source: bootcd/isolinux/syslinux-6.03/core/idle.c

/* ----------------------------------------------------------------------- *
 *   
 *   Copyright 2008 H. Peter Anvin - All Rights Reserved
 *   Copyright 2009-2010 Intel Corporation; author: H. Peter Anvin
 *
 *   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, Inc., 51 Franklin St, Fifth Floor,
 *   Boston MA 02110-1301, USA; either version 2 of the License, or
 *   (at your option) any later version; incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

/*
 * idle.c:
 *
 * This function provided protected-mode access to the idle handling.
 * It needs to be carefully coordinated with idle.inc, which provides
 * idle services to real-mode code.
 */

#include "core.h"
#include <sys/cpu.h>

#define TICKS_TO_IDLE   4       /* Also in idle.inc */

static jiffies_t _IdleTimer;
__export uint16_t NoHalt = 0;

int (*idle_hook_func)(void);

void reset_idle(void)
{
    _IdleTimer = jiffies();
    sti();      /* Guard against BIOS/PXE brokenness... */
}

__export void __idle(void)
{
    if (jiffies() - _IdleTimer < TICKS_TO_IDLE)
        return;

    if (idle_hook_func && idle_hook_func())
        return;                 /* Nonzero return = do not idle */

    sti();
    if (NoHalt)
        cpu_relax();
    else
        hlt();
}