include/asm-blackfin/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 #endif
  35
  36 #endif