LXR linux/arch/v850/kernel/v850e

   1/*
   2 * include/asm-v850/v850e_utils.h -- Utility functions associated with
   3 *      V850E CPUs
   4 *
   5 *  Copyright (C) 2001,02,03  NEC Electronics Corporation
   6 *  Copyright (C) 2001,02,03  Miles Bader <miles@gnu.org>
   7 *
   8 * This file is subject to the terms and conditions of the GNU General
   9 * Public License.  See the file COPYING in the main directory of this
  10 * archive for more details.
  11 *
  12 * Written by Miles Bader <miles@gnu.org>
  13 */
  14
  15#include <asm/v850e_utils.h>
  16
  17/* Calculate counter clock-divider and count values to attain the
  18   desired frequency RATE from the base frequency BASE_FREQ.  The
  19   counter is expected to have a clock-divider, which can divide the
  20   system cpu clock by a power of two value from MIN_DIVLOG2 to
  21   MAX_DIV_LOG2, and a word-size of COUNTER_SIZE bits (the counter
  22   counts up and resets whenever it's equal to the compare register,
  23   generating an interrupt or whatever when it does so).  The returned
  24   values are: *DIVLOG2 -- log2 of the desired clock divider and *COUNT
  25   -- the counter compare value to use.  Returns true if it was possible
  26   to find a reasonable value, otherwise false (and the other return
  27   values will be set to be as good as possible).  */
  28int calc_counter_params (unsigned long base_freq,
  29                         unsigned long rate,
  30                         unsigned min_divlog2, unsigned max_divlog2,
  31                         unsigned counter_size,
  32                         unsigned *divlog2, unsigned *count)
  33{
  34        unsigned _divlog2;
  35        int ok = 0;
  36
  37        /* Find the lowest clock divider setting that can represent RATE.  */
  38        for (_divlog2 = min_divlog2; _divlog2 <= max_divlog2; _divlog2++) {
  39                /* Minimum interrupt rate possible using this divider.  */
  40                unsigned min_int_rate
  41                        = (base_freq >> _divlog2) >> counter_size;
  42
  43                if (min_int_rate <= rate) {
  44                        /* This setting is the highest resolution
  45                           setting that's slow enough enough to attain
  46                           RATE interrupts per second, so use it.  */
  47                        ok = 1;
  48                        break;
  49                }
  50        }
  51
  52        if (_divlog2 > max_divlog2)
  53                /* Can't find correct setting.  */
  54                _divlog2 = max_divlog2;
  55
  56        if (divlog2)
  57                *divlog2 = _divlog2;
  58        if (count)
  59                *count = ((base_freq >> _divlog2) + rate/2) / rate;
  60
  61        return ok;
  62}
  63