LXR linux/arch/blackfin/include/asm/time.h

   1/*
   2 * asm-blackfin/time.h:
   3 *
   4 * Copyright 2004-2008 Analog Devices Inc.
   5 *
   6 * Licensed under the GPL-2 or later.
   7 */
   8
   9#ifndef _ASM_BLACKFIN_TIME_H
  10#define _ASM_BLACKFIN_TIME_H
  11
  12/*
  13 * The way that the Blackfin core timer works is:
  14 *  - CCLK is divided by a programmable 8-bit pre-scaler (TSCALE)
  15 *  - Every time TSCALE ticks, a 32bit is counted down (TCOUNT)
  16 *
  17 * If you take the fastest clock (1ns, or 1GHz to make the math work easier)
  18 *    10ms is 10,000,000 clock ticks, which fits easy into a 32-bit counter
  19 *    (32 bit counter is 4,294,967,296ns or 4.2 seconds) so, we don't need
  20 *    to use TSCALE, and program it to zero (which is pass CCLK through).
  21 *    If you feel like using it, try to keep HZ * TIMESCALE to some
  22 *    value that divides easy (like power of 2).
  23 */
  24
  25#ifndef CONFIG_CPU_FREQ
  26# define TIME_SCALE 1
  27#else
  28/*
  29 * Blackfin CPU frequency scaling supports max Core Clock 1, 1/2 and 1/4 .
  30 * Whenever we change the Core Clock frequency changes we immediately
  31 * adjust the Core Timer Presale Register. This way we don't lose time.
  32 */
  33#define TIME_SCALE 4
  34
  35# ifdef CONFIG_CYCLES_CLOCKSOURCE
  36extern unsigned long long __bfin_cycles_off;
  37extern unsigned int __bfin_cycles_mod;
  38# endif
  39#endif
  40
  41#if defined(CONFIG_TICKSOURCE_CORETMR)
  42extern void bfin_coretmr_init(void);
  43extern void bfin_coretmr_clockevent_init(void);
  44#endif
  45
  46#endif
  47