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highres_timer.c

/*
 * arch/v850/kernel/highres_timer.c -- High resolution timing routines
 *
 *  Copyright (C) 2001,02,03  NEC Electronics Corporation
 *  Copyright (C) 2001,02,03  Miles Bader <miles@gnu.org>
 *
 * This file is subject to the terms and conditions of the GNU General
 * Public License.  See the file COPYING in the main directory of this
 * archive for more details.
 *
 * Written by Miles Bader <miles@gnu.org>
 */

#include <asm/system.h>
#include <asm/v850e_timer_d.h>
#include <asm/highres_timer.h>

#define HIGHRES_TIMER_USEC_SHIFT   12

/* Pre-calculated constant used for converting ticks to real time
   units.  We initialize it to prevent it being put into BSS.  */
static u32 highres_timer_usec_prescale = 1;

void highres_timer_slow_tick_irq (void) __attribute__ ((noreturn));
void highres_timer_slow_tick_irq (void)
{
      /* This is an interrupt handler, so it must be very careful to
         not to trash any registers.  At this point, the stack-pointer
         (r3) has been saved in the chip ram location ENTRY_SP by the
         interrupt vector, so we can use it as a scratch register; we
         must also restore it before returning.  */
      asm ("ld.w  %0[r0], sp;"
           "add   1, sp;"
           "st.w  sp, %0[r0];"
           "ld.w  %1[r0], sp;" /* restore pre-irq stack-pointer */
           "reti"
           ::
            "i" (HIGHRES_TIMER_SLOW_TICKS_ADDR),
            "i" (ENTRY_SP_ADDR)
           : "memory");
}

void highres_timer_reset (void)
{
      V850E_TIMER_D_TMD (HIGHRES_TIMER_TIMER_D_UNIT) = 0;
      HIGHRES_TIMER_SLOW_TICKS = 0;
}

void highres_timer_start (void)
{
      u32 fast_tick_rate;

      /* Start hardware timer.  */
      v850e_timer_d_configure (HIGHRES_TIMER_TIMER_D_UNIT,
                         HIGHRES_TIMER_SLOW_TICK_RATE);

      fast_tick_rate =
            (V850E_TIMER_D_BASE_FREQ
             >> V850E_TIMER_D_DIVLOG2 (HIGHRES_TIMER_TIMER_D_UNIT));

      /* The obvious way of calculating microseconds from fast ticks
         is to do:

           usec = fast_ticks * 10^6 / fast_tick_rate

         However, divisions are much slower than multiplications, and
         the above calculation can overflow, so we do this instead:

           usec = fast_ticks * (10^6 * 2^12 / fast_tick_rate) / 2^12

           since we can pre-calculate (10^6 * (2^12 / fast_tick_rate))
         and use a shift for dividing by 2^12, this avoids division,
         and is almost as accurate (it differs by about 2 microseconds
         at the extreme value of the fast-tick counter's ranger).  */
      highres_timer_usec_prescale = ((1000000 << HIGHRES_TIMER_USEC_SHIFT)
                               / fast_tick_rate);

      /* Enable the interrupt (which is hardwired to this use), and
         give it the highest priority.  */
      V850E_INTC_IC (IRQ_INTCMD (HIGHRES_TIMER_TIMER_D_UNIT)) = 0;
}

void highres_timer_stop (void)
{
      /* Stop the timer.  */
      V850E_TIMER_D_TMCD (HIGHRES_TIMER_TIMER_D_UNIT) =
            V850E_TIMER_D_TMCD_CAE;
      /* Disable its interrupt, just in case.  */
      v850e_intc_disable_irq (IRQ_INTCMD (HIGHRES_TIMER_TIMER_D_UNIT));
}

inline void highres_timer_read_ticks (u32 *slow_ticks, u32 *fast_ticks)
{
      int flags;
      u32 fast_ticks_1, fast_ticks_2, _slow_ticks;

      local_irq_save (flags);
      fast_ticks_1 = V850E_TIMER_D_TMD (HIGHRES_TIMER_TIMER_D_UNIT);
      _slow_ticks = HIGHRES_TIMER_SLOW_TICKS;
      fast_ticks_2 = V850E_TIMER_D_TMD (HIGHRES_TIMER_TIMER_D_UNIT);
      local_irq_restore (flags);

      if (fast_ticks_2 < fast_ticks_1)
            _slow_ticks++;

      *slow_ticks = _slow_ticks;
      *fast_ticks = fast_ticks_2;
}

inline void highres_timer_ticks_to_timeval (u32 slow_ticks, u32 fast_ticks,
                                  struct timeval *tv)
{
      unsigned long sec, sec_rem, usec;

      usec = ((fast_ticks * highres_timer_usec_prescale)
            >> HIGHRES_TIMER_USEC_SHIFT);

      sec = slow_ticks / HIGHRES_TIMER_SLOW_TICK_RATE;
      sec_rem = slow_ticks % HIGHRES_TIMER_SLOW_TICK_RATE;

      usec += sec_rem * (1000000 / HIGHRES_TIMER_SLOW_TICK_RATE);

      tv->tv_sec = sec;
      tv->tv_usec = usec;
}

void highres_timer_read (struct timeval *tv)
{
      u32 fast_ticks, slow_ticks;
      highres_timer_read_ticks (&slow_ticks, &fast_ticks);
      highres_timer_ticks_to_timeval (slow_ticks, fast_ticks, tv);
}

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