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/* tick.c -- Simulation of OpenRISC 1000 tick timer

   Copyright (C) 1999 Damjan Lampret, lampret@opencores.org

   Copyright (C) 2005 György `nog' Jeney, nog@sdf.lonestar.org

   Copyright (C) 2008 Embecosm Limited

   Contributor Jeremy Bennett <jeremy.bennett@embecosm.com>

   This file is part of Or1ksim, the OpenRISC 1000 Architectural Simulator.

   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/>.  */

/* This program is commented throughout in a fashion suitable for processing

   with Doxygen. */

/* This is functional simulation of OpenRISC 1000 architectural tick timer */

/* Autoconf and/or portability configuration */

#include "config.h"

#include "port.h"

/* System includes */

#include <stdlib.h>

#include <stdio.h>

/* Package includes */

#include "arch.h"

#include "abstract.h"

#include "except.h"

#include "tick.h"

#include "opcode/or32.h"

#include "spr-defs.h"

#include "execute.h"

#include "pic.h"

#include "sprs.h"

#include "sim-config.h"

#include "sched.h"

/*! When did the timer start to count */

static long long cycle_count_at_tick_start = 0;

/*! Indicates if the timer is actually counting.  Needed to simulate one-shot

    mode correctly */

int tick_counting;

/*! Reset. It initializes TTCR register. */

void

tick_reset (void)

{

  if (config.sim.verbose)

    {

      PRINTF ("Resetting Tick Timer.\n");

    }

  cpu_state.sprs[SPR_TTCR] = 0;

  cpu_state.sprs[SPR_TTMR] = 0;

  tick_counting = 0;

}

/*! Raises a timer exception */

static void

tick_raise_except (void *dat)

{

  cpu_state.sprs[SPR_TTMR] |= SPR_TTMR_IP;

  /* Reschedule unconditionally, since we have to raise the exception until

   * TTMR_IP has been cleared */

  sched_next_insn (tick_raise_except, NULL);

  /* be sure not to issue a timer exception if an exception occured before it */

  if (cpu_state.sprs[SPR_SR] & SPR_SR_TEE)

    {

      except_handle (EXCEPT_TICK, cpu_state.sprs[SPR_EEAR_BASE]);

    }

}

/*! Restarts the tick timer */

static void

tick_restart (void *dat)

{

  cpu_state.sprs[SPR_TTCR] = 0;

  cycle_count_at_tick_start = runtime.sim.cycles;

  SCHED_ADD (tick_restart, NULL, cpu_state.sprs[SPR_TTMR] & SPR_TTMR_TP);

}

/*! Stops the timer */

static void

tick_one_shot (void *dat)

{

  cpu_state.sprs[SPR_TTCR] = cpu_state.sprs[SPR_TTMR] & SPR_TTMR_TP;

  tick_counting = 0;

}

/*! Schedules the timer jobs */

static void

sched_timer_job (uorreg_t prev_ttmr)

{

  uorreg_t ttmr = cpu_state.sprs[SPR_TTMR];

  uint32_t match_ttmr = ttmr & SPR_TTMR_TP;

  /* TTCR register, only concerned with part of TTCR which will trigger int */

  uint32_t match_ttcr = spr_read_ttcr () & SPR_TTMR_TP;

  uint32_t cycles_until_except;

  /* On clearing TTMR interrupt signal bit remove previous jobs if they

     exist */

  if ((prev_ttmr & SPR_TTMR_IE) && !(ttmr & SPR_TTMR_IP))

    {

      SCHED_FIND_REMOVE (tick_raise_except, NULL);

    }

  switch (prev_ttmr & SPR_TTMR_M)

    {

    case SPR_TTMR_RT:

      SCHED_FIND_REMOVE (tick_restart, NULL);

      break;

    case SPR_TTMR_SR:

      SCHED_FIND_REMOVE (tick_one_shot, NULL);

      break;

    }

  /* Calculate cycles until next tick exception, based on current TTCR value */

  if (match_ttmr >= match_ttcr)

    {

      cycles_until_except = match_ttmr - match_ttcr;

    }

  else

    {

      /* Cycles after "wrap" of section of TTCR which will cause a match and,

         potentially, an exception */

      cycles_until_except = match_ttmr + (0x0fffffffu - match_ttcr) + 1;

    }

  switch (ttmr & SPR_TTMR_M)

    {

    case 0:                      /* Disabled timer */

      if (!cycles_until_except && (ttmr & SPR_TTMR_IE) && !(ttmr & SPR_TTMR_IP))

        SCHED_ADD (tick_raise_except, NULL, 0);

      break;

    case SPR_TTMR_RT:           /* Auto-restart timer */

      SCHED_ADD (tick_restart, NULL, cycles_until_except);

      if ((ttmr & SPR_TTMR_IE) && !(ttmr & SPR_TTMR_IP))

        SCHED_ADD (tick_raise_except, NULL, cycles_until_except);

      break;

    case SPR_TTMR_SR:           /* One-shot timer */

      if (tick_counting)

        {

          SCHED_ADD (tick_one_shot, NULL, cycles_until_except);

          if ((ttmr & SPR_TTMR_IE) && !(ttmr & SPR_TTMR_IP))

            SCHED_ADD (tick_raise_except, NULL, cycles_until_except);

        }

      break;

    case SPR_TTMR_CR:           /* Continuos timer */

      if ((ttmr & SPR_TTMR_IE) && !(ttmr & SPR_TTMR_IP))

        SCHED_ADD (tick_raise_except, NULL, cycles_until_except);

    }

}

/*! Handles a write to the ttcr spr */

void

spr_write_ttcr (uorreg_t value)

{

  cycle_count_at_tick_start = runtime.sim.cycles - value;

  sched_timer_job (cpu_state.sprs[SPR_TTMR]);

}

/*! prev_val is the *previous* value of SPR_TTMR.  The new one can be found in

    cpu_state.sprs[SPR_TTMR] */

void

spr_write_ttmr (uorreg_t prev_val)

{

  uorreg_t value = cpu_state.sprs[SPR_TTMR];

  /* Code running on or1k can't set SPR_TTMR_IP so make sure it isn't */

  cpu_state.sprs[SPR_TTMR] &= ~SPR_TTMR_IP;

  /* If the timer was already disabled, ttcr should not be updated */

  if (tick_counting)

    {

      cpu_state.sprs[SPR_TTCR] = runtime.sim.cycles - cycle_count_at_tick_start;

    }

  cycle_count_at_tick_start = runtime.sim.cycles - cpu_state.sprs[SPR_TTCR];

  tick_counting = value & SPR_TTMR_M;

  /* If TTCR==TTMR_TP when setting MR, we disable counting??

     I think this should be looked at - Julius */

  if ((tick_counting == SPR_TTMR_CR) &&

      (cpu_state.sprs[SPR_TTCR] == (value & SPR_TTMR_TP)))

    {

      tick_counting = 0;

    }

  sched_timer_job (prev_val);

}

uorreg_t

spr_read_ttcr ()

{

  uorreg_t ret;

  if (!tick_counting)

    {

      /* Report the time when the counter stopped (and don't carry on

         counting) */

      ret = cpu_state.sprs[SPR_TTCR];

    }

  else

    {

      ret = runtime.sim.cycles - cycle_count_at_tick_start;

    }

  return  ret;

}