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/* clockedf.c - support routines for alternate clock rate
              - this is the FAR version of clocked.c for loadable drivers

  altclk_in(hz, fn) - install routine with specified rate
                          "hz" should be a multiple of system rate of 100 Hz

  altclk_out()      - uninstall alternate clock routine and restore system rate
			return old value of "altclk"

  altclk_rate(hz)   - set clock interrupt rate
			new rate must be an even multiple of system rate "HZ"
			return 0 if completed ok, -1 otherwise

  History:
    90/08/08 hws	initial version, works with hs.c modified for com[1-4]
    90/08/14 hws	make it more like a Unix system call
    90/09/12 hws	add far version
*/

#include	<sys/coherent.h>	/* altclk */
#include	<sys/const.h>	/* HZ */

#define	PIT	0x40	/* 8253 port */
#define	TMR0_M3	0x36	/* timer 0, mode 3 */
#if 0
/* nominal IBM rate is 1.1900 MHz */
#define	SYS_HZ	1190000L	/* rate of input clock to timer 0 */
#else
/* current kernel rate is 1.1932 MHz */
#define	SYS_HZ	1193200L	/* rate of input clock to timer 0 */
#endif

typedef int (*PFI)();	/* pointer to function returning int */

extern saddr_t ucs;

static int altclk_rate(hz)
unsigned int hz;
{
  int s;	/* to save CPU irpt flag */
  unsigned int interval;	/* period for hz, in units of 1.19 MHz ticks */
  int ret;

  if (hz >= HZ && hz % HZ == 0) {	/* can't go slower than HZ! */
    interval = SYS_HZ/hz;
    s = sphi();	/* disable irpts */
    outb(PIT+3, TMR0_M3);
    outb(PIT, interval & 0xff);
    outb(PIT, interval >> 8);	/* unsigned shift */
    spl(s);	/* restore previous irpt state */
    ret = 0;
  }
  else {
    ret = -1;
  }
  return ret;
}

int altclk_in(hz, fn)
int hz;
PFI fn;
{
  int ret;
  int s;

  if ((ret = altclk_rate(hz)) == 0) {
    s = sphi();
    altclk = fn;
    altsel = cs_sel();
    spl(s);
  }
  return ret;
}

PFI altclk_out()
{
  PFI ret;
  int s;

  ret = altclk;
  if (ret) {
    altclk_rate(HZ);
    s = sphi();
    altclk = 0;
    altsel = 0;
    spl(s);
  }
  return ret;
}

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