arch/all-pc/kernel/kernel_timer.h

   1 #include <hardware/pit.h>
   2
   3 /*
   4  * Start up channel 0 in 'terminal count' mode (mode 0).
   5  * It will count down to zero, and then will issue a single interrupt,
   6  * but we don't care about it since interrupts are neither used nor enabled.
   7  * It's safe to use the timer freely here. timer.device starts up long after
   8  * this code.
   9  */
  10 static inline void pit_start(unsigned short start)
  11 {
  12     outb(CH0|ACCESS_FULL|MODE_TERMINAL, PIT_CONTROL);
  13     ch_write(start, PIT_CH0);
  14 }
  15
  16 /*
  17  * In this mode the counter wraps around to 0xFFFF and continues decrementing.
  18  * It's assumed that the start value is reasonably lower, and the CPU has time
  19  * to detect the wraparound.
  20  */
  21 static inline unsigned short pit_wait(unsigned short start)
  22 {
  23     unsigned short tick;
  24
  25     do
  26     {
  27         outb(CH0|ACCESS_LATCH, PIT_CONTROL);
  28         tick = ch_read(PIT_CH0);
  29     } while ((tick > 0) && (tick < start));
  30
  31     return tick;
  32 }
  33
  34 void pit_udelay(unsigned int usec);