text: /*-
   * Copyright (c) 1998 Michael Smith <msmith@freebsd.org>
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   */
  
  #include <sys/cdefs.h>
  __FBSDID("$FreeBSD: soc2013/dpl/head/sys/boot/i386/libi386/time.c 229064 2011-12-21 16:47:01Z ed $");
  
  #include <stand.h>
  #include <btxv86.h>
  #include "bootstrap.h"
  #include "libi386.h"
  
  static int	bios_seconds(void);
  
  /*
   * Return the BIOS time-of-day value.
   *
   * XXX uses undocumented BCD support from libstand.
   */
  static int
  bios_seconds(void)
  {
      int			hr, minute, sec;
      
      v86.ctl = 0;
      v86.addr = 0x1a;		/* int 0x1a, function 2 */
      v86.eax = 0x0200;
      v86int();
  
      hr = bcd2bin((v86.ecx & 0xff00) >> 8);	/* hour in %ch */
      minute = bcd2bin(v86.ecx & 0xff);		/* minute in %cl */
      sec = bcd2bin((v86.edx & 0xff00) >> 8);	/* second in %dh */
      
      return (hr * 3600 + minute * 60 + sec);
  }
  
  /*
   * Return the time in seconds since the beginning of the day.
   *
   * Some BIOSes (notably qemu) don't correctly read the RTC
   * registers in an atomic way, sometimes returning bogus values.
   * Therefore we "debounce" the reading by accepting it only when
   * we got 8 identical values in succession.
   *
   * If we pass midnight, don't wrap back to 0.
   */
  time_t
  time(time_t *t)
  {
      static time_t lasttime;
      time_t now, check;
      int same, try;
  
      same = try = 0;
      check = bios_seconds();
      do {
  	now = check;
  	check = bios_seconds();
  	if (check != now)
  	    same = 0;
      } while (++same < 8 && ++try < 1000);
  
      if (now < lasttime)
  	now += 24 * 3600;
      lasttime = now;
      
      if (t != NULL)
  	*t = now;
      return(now);
  }
  
  /*
   * Use the BIOS Wait function to pause for (period) microseconds.
   *
   * Resolution of this function is variable, but typically around
   * 1ms.
   */
  void
  delay(int period)
  {
      v86.ctl = 0;
      v86.addr = 0x15;		/* int 0x15, function 0x86 */
      v86.eax = 0x8600;
      v86.ecx = period >> 16;
      v86.edx = period & 0xffff;
      v86int();
  }
  