kernel / pub / scm / linux / kernel / git / iwamatsu / linux-stable / refs/heads/linux-2.6.18.y / . / arch / v850 / kernel / 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; | |

} |