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v850e_utils.c

/*
 * include/asm-v850/v850e_utils.h -- Utility functions associated with
 *    V850E CPUs
 *
 *  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/v850e_utils.h>

/* Calculate counter clock-divider and count values to attain the
   desired frequency RATE from the base frequency BASE_FREQ.  The
   counter is expected to have a clock-divider, which can divide the
   system cpu clock by a power of two value from MIN_DIVLOG2 to
   MAX_DIV_LOG2, and a word-size of COUNTER_SIZE bits (the counter
   counts up and resets whenever it's equal to the compare register,
   generating an interrupt or whatever when it does so).  The returned
   values are: *DIVLOG2 -- log2 of the desired clock divider and *COUNT
   -- the counter compare value to use.  Returns true if it was possible
   to find a reasonable value, otherwise false (and the other return
   values will be set to be as good as possible).  */
int calc_counter_params (unsigned long base_freq,
                   unsigned long rate,
                   unsigned min_divlog2, unsigned max_divlog2,
                   unsigned counter_size,
                   unsigned *divlog2, unsigned *count)
{
      unsigned _divlog2;
      int ok = 0;

      /* Find the lowest clock divider setting that can represent RATE.  */
      for (_divlog2 = min_divlog2; _divlog2 <= max_divlog2; _divlog2++) {
            /* Minimum interrupt rate possible using this divider.  */
            unsigned min_int_rate
                  = (base_freq >> _divlog2) >> counter_size;

            if (min_int_rate <= rate) {
                  /* This setting is the highest resolution
                     setting that's slow enough enough to attain
                     RATE interrupts per second, so use it.  */
                  ok = 1;
                  break;
            }
      }

      if (_divlog2 > max_divlog2)
            /* Can't find correct setting.  */
            _divlog2 = max_divlog2;

      if (divlog2)
            *divlog2 = _divlog2;
      if (count)
            *count = ((base_freq >> _divlog2) + rate/2) / rate;

      return ok;
}

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