x15/kern/timer.h

/*
 * Copyright (c) 2017 Richard Braun.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *
 * Low resolution timer system.
 */

#ifndef KERN_TIMER_H
#define KERN_TIMER_H

#include <stdint.h>

#include <kern/hlist.h>
#include <kern/init.h>
#include <kern/work.h>

// Scheduling flags.
#define TIMER_DETACHED      0x1   // Timer completion isn't synchronized.
#define TIMER_INTR          0x2   // Handler is run from interrupt context.
#define TIMER_HIGH_PRIO     0x4   // Handler is run in high priority thread.

struct timer;

// Type for timer functions.
typedef void (*timer_fn_t) (struct timer *);

/*
 * Locking keys :
 * (c) cpu_data
 * (a) atomic
 *
 * (*) The cpu member is used to determine which lock serializes access to
 * the structure. It must be accessed atomically, but updated while the
 * timer is locked.
 */
struct timer
{
  union
    {
      struct hlist_node node;   // (c)
      struct work work;
    };

  uint64_t ticks;             // (c)
  timer_fn_t fn;
  unsigned int cpu;           // (c,a,*)
  unsigned short state;       // (c)
  unsigned short flags;       // (c)
  struct thread *joiner;      // (c)
};


/*
 * Return the absolute expiration time of the timer, in ticks.
 *
 * This function may not be called while another thread is scheduling the
 * timer.
 */
static inline uint64_t
timer_get_time (const struct timer *timer)
{
  return (timer->ticks);
}

/*
 * Initialize a timer.
 *
 * Timers that are reponsible for releasing their own resources must
 * be detached.
 */
void timer_init (struct timer *timer, timer_fn_t fn, int flags);

/*
 * Schedule a timer.
 *
 * The time of expiration is an absolute time in ticks.
 *
 * Timers may safely be rescheduled after completion. Periodic timers are
 * implemented by rescheduling from the handler.
 *
 * If the timer has been canceled, this function does nothing. A
 * canceled timer must be reinitialized before being scheduled again.
 *
 * This function may safely be called in interrupt context.
 */
void timer_schedule (struct timer *timer, uint64_t ticks);

/*
 * Cancel a timer.
 *
 * The given timer must not be detached.
 *
 * If the timer has already expired, this function waits until the timer
 * function completes, or returns immediately if the function has already
 * completed.
 *
 * This function may safely be called from the timer handler, but not on
 * the current timer. Canceling a timer from the handler is achieved by
 * simply not rescheduling it.
 */
void timer_cancel (struct timer *timer);

/*
 * Report a periodic event on the current processor.
 *
 * Interrupts and preemption must be disabled when calling this function.
 */
void timer_report_periodic_event (void);

/*
 * This init operation provides :
 *  - timer initialization and scheduling
 */
INIT_OP_DECLARE (timer_bootstrap);

#endif