timer.c

#include "timer.h"

// a scratch area per CPU for machine-mode timer interrupts.
reg_t timer_scratch[NCPU][5];

#define interval 20000000 // cycles; about 2 second in qemu.

void timer_init()
{
  // each CPU has a separate source of timer interrupts.
  int id = r_mhartid();

  // ask the CLINT for a timer interrupt.
  // int interval = 1000000; // cycles; about 1/10th second in qemu.

  *(reg_t *)CLINT_MTIMECMP(id) = *(reg_t *)CLINT_MTIME + interval;

  // prepare information in scratch[] for timervec.
  // scratch[0..2] : space for timervec to save registers.
  // scratch[3] : address of CLINT MTIMECMP register.
  // scratch[4] : desired interval (in cycles) between timer interrupts.
  reg_t *scratch = &timer_scratch[id][0];
  scratch[3] = CLINT_MTIMECMP(id);
  scratch[4] = interval;
  w_mscratch((reg_t)scratch);

  // enable machine-mode timer interrupts.
  w_mie(r_mie() | MIE_MTIE);
}

static int timer_count = 0;

void timer_handler()
{
  lib_printf("timer_handler: %d\n", ++timer_count);
  int id = r_mhartid();
  *(reg_t *)CLINT_MTIMECMP(id) = *(reg_t *)CLINT_MTIME + interval;
}