Bochs/bochs/iodev/pit82c54.cc

/////////////////////////////////////////////////////////////////////////
// $Id: pit82c54.cc,v 1.36 2009-02-08 09:05:52 vruppert Exp $
/////////////////////////////////////////////////////////////////////////
//
//  Copyright (C) 2001  The Bochs Project
//
//  This library is free software; you can redistribute it and/or
//  modify it under the terms of the GNU Lesser General Public
//  License as published by the Free Software Foundation; either
//  version 2 of the License, or (at your option) any later version.
//
//  This library 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
//  Lesser General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public
//  License along with this library; if not, write to the Free Software
//  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA

/*
 * Emulator of an Intel 8254/82C54 Programmable Interval Timer.
 * Greg Alexander <yakovlev@usa.com>
 *
 *
 * Things I am unclear on (greg):
 * 1.)What happens if both the status and count registers are latched,
 *  but the first of the two count registers has already been read?
 *  I.E.:
 *   latch count 0 (16-bit)
 *   Read count 0 (read LSByte)
 *   READ_BACK status of count 0
 *   Read count 0 - do you get MSByte or status?
 *  This will be flagged as an error.
 * 2.)What happens when we latch the output in the middle of a 2-part
 *  unlatched read?
 * 3.)I assumed that programming a counter removes a latched status.
 * 4.)I implemented the 8254 description of mode 0, not the 82C54 one.
 * 5.)clock() calls represent a rising clock edge followed by a falling
 *  clock edge.
 * 6.)What happens when we trigger mode 1 in the middle of a 2-part
 *  write?
 */

// Define BX_PLUGGABLE in files that can be compiled into plugins.  For
// platforms that require a special tag on exported symbols, BX_PLUGGABLE
// is used to know when we are exporting symbols and when we are importing.
#define BX_PLUGGABLE

#include "iodev.h"
#include "pit82c54.h"
#define LOG_THIS this->


void pit_82C54::print_counter(counter_type &thisctr)
{
  BX_INFO(("Printing Counter"));
  BX_INFO(("count: %d",thisctr.count));
  BX_INFO(("count_binary: %x",thisctr.count_binary));
  BX_INFO(("counter gate: %x",thisctr.GATE));
  BX_INFO(("counter OUT: %x",thisctr.OUTpin));
  BX_INFO(("next_change_time: %d",thisctr.next_change_time));
  BX_INFO(("End Counter Printout"));
}

void pit_82C54::print_cnum(Bit8u cnum)
{
  if (cnum>MAX_COUNTER) {
    BX_ERROR(("Bad counter index to print_cnum"));
  } else {
    print_counter(counter[cnum]);
  }
}

void pit_82C54::latch_counter(counter_type &thisctr)
{
    if (thisctr.count_LSB_latched || thisctr.count_MSB_latched) {
      //Do nothing because previous latch has not been read.;
    } else {
      switch(thisctr.read_state) {
      case MSByte:
        thisctr.outlatch=thisctr.count & 0xFFFF;
        thisctr.count_MSB_latched=1;
        break;
      case LSByte:
        thisctr.outlatch=thisctr.count & 0xFFFF;
        thisctr.count_LSB_latched=1;
        break;
      case LSByte_multiple:
        thisctr.outlatch=thisctr.count & 0xFFFF;
        thisctr.count_LSB_latched=1;
        thisctr.count_MSB_latched=1;
        break;
      case MSByte_multiple:
        if (!(seen_problems & UNL_2P_READ)) {
//          seen_problems|=UNL_2P_READ;
          BX_ERROR(("Unknown behavior when latching during 2-part read."));
          BX_ERROR(("  This message will not be repeated."));
        }
        //I guess latching and resetting to LSB first makes sense;
        BX_DEBUG(("Setting read_state to LSB_mult"));
        thisctr.read_state=LSByte_multiple;
        thisctr.outlatch=thisctr.count & 0xFFFF;
        thisctr.count_LSB_latched=1;
        thisctr.count_MSB_latched=1;
        break;
      default:
        BX_ERROR(("Unknown read mode found during latch command."));
        break;
      }
    }
}

void pit_82C54::set_OUT(counter_type &thisctr, bx_bool data)
{
  if (thisctr.OUTpin != data) {
    thisctr.OUTpin = data;
    if (thisctr.out_handler != NULL) {
      thisctr.out_handler(data);
    }
  }
}

  void BX_CPP_AttrRegparmN(2)
pit_82C54::set_count (counter_type &thisctr, Bit32u data)
{
  thisctr.count=data & 0xFFFF;
  set_binary_to_count(thisctr);
}

  void BX_CPP_AttrRegparmN(1)
pit_82C54::set_count_to_binary(counter_type &thisctr)
{
  if (thisctr.bcd_mode) {
    thisctr.count=
      (((thisctr.count_binary/1)%10)<<0) |
      (((thisctr.count_binary/10)%10)<<4) |
      (((thisctr.count_binary/100)%10)<<8) |
      (((thisctr.count_binary/1000)%10)<<12);
  } else {
    thisctr.count=thisctr.count_binary;
  }
}

  void BX_CPP_AttrRegparmN(1)
pit_82C54::set_binary_to_count(counter_type &thisctr)
{
  if (thisctr.bcd_mode) {
    thisctr.count_binary=
      (1*((thisctr.count>>0)&0xF)) +
      (10*((thisctr.count>>4)&0xF)) +
      (100*((thisctr.count>>8)&0xF)) +
      (1000*((thisctr.count>>12)&0xF));
  } else {
    thisctr.count_binary=thisctr.count;
  }
}

  void BX_CPP_AttrRegparmN(1)
pit_82C54::decrement (counter_type &thisctr)
{
  if (!thisctr.count) {
    if (thisctr.bcd_mode) {
      thisctr.count=0x9999;
      thisctr.count_binary=9999;
    } else {
      thisctr.count=0xFFFF;
      thisctr.count_binary=0xFFFF;
    }
  } else {
    thisctr.count_binary--;
    set_count_to_binary(thisctr);
  }
}

void pit_82C54::init(void)
{
  put("PIT81");

  for(int i=0;i<3;i++) {
    BX_DEBUG(("Setting read_state to LSB"));
    counter[i].read_state=LSByte;
    counter[i].write_state=LSByte;
    counter[i].GATE=1;
    counter[i].OUTpin=1;
    counter[i].triggerGATE=0;
    counter[i].mode=4;
    counter[i].first_pass=0;
    counter[i].bcd_mode=0;
    counter[i].count=0;
    counter[i].count_binary=0;
    counter[i].state_bit_1=0;
    counter[i].state_bit_2=0;
    counter[i].null_count=0;
    counter[i].rw_mode=1;
    counter[i].count_written=1;
    counter[i].count_LSB_latched=0;
    counter[i].count_MSB_latched=0;
    counter[i].status_latched=0;
    counter[i].next_change_time=0;
    counter[i].out_handler=NULL;
  }
  seen_problems=0;
}

pit_82C54::pit_82C54(void)
{
  init();
}

void pit_82C54::reset(unsigned type) {}

void pit_82C54::register_state(bx_param_c *parent)
{
  char name[4];

  for (unsigned i=0; i<3; i++) {
    sprintf(name, "%d", i);
    bx_list_c *tim = new bx_list_c(parent, name, 22);
    new bx_shadow_bool_c(tim, "GATE", &counter[i].GATE);
    new bx_shadow_bool_c(tim, "OUTpin", &counter[i].OUTpin);
    new bx_shadow_num_c(tim, "count", &counter[i].count);
    new bx_shadow_num_c(tim, "outlatch", &counter[i].outlatch);
    new bx_shadow_num_c(tim, "inlatch", &counter[i].inlatch);
    new bx_shadow_num_c(tim, "status_latch", &counter[i].status_latch);
    new bx_shadow_num_c(tim, "rw_mode", &counter[i].rw_mode);
    new bx_shadow_num_c(tim, "mode", &counter[i].mode);
    new bx_shadow_bool_c(tim, "bcd_mode", &counter[i].bcd_mode);
    new bx_shadow_bool_c(tim, "null_count", &counter[i].null_count);
    new bx_shadow_bool_c(tim, "count_LSB_latched", &counter[i].count_LSB_latched);
    new bx_shadow_bool_c(tim, "count_MSB_latched", &counter[i].count_MSB_latched);
    new bx_shadow_bool_c(tim, "status_latched", &counter[i].status_latched);
    new bx_shadow_num_c(tim, "count_binary", &counter[i].count_binary);
    new bx_shadow_bool_c(tim, "triggerGATE", &counter[i].triggerGATE);
    new bx_shadow_num_c(tim, "write_state", (Bit8u*)&counter[i].write_state);
    new bx_shadow_num_c(tim, "read_state", (Bit8u*)&counter[i].read_state);
    new bx_shadow_bool_c(tim, "count_written", &counter[i].count_written);
    new bx_shadow_bool_c(tim, "first_pass", &counter[i].first_pass);
    new bx_shadow_bool_c(tim, "state_bit_1", &counter[i].state_bit_1);
    new bx_shadow_bool_c(tim, "state_bit_2", &counter[i].state_bit_2);
    new bx_shadow_num_c(tim, "next_change_time", &counter[i].next_change_time);
  }
}

void  BX_CPP_AttrRegparmN(2)
pit_82C54::decrement_multiple(counter_type &thisctr, Bit32u cycles)
{
  while(cycles>0) {
    if (cycles<=thisctr.count_binary) {
      thisctr.count_binary-=cycles;
      cycles-=cycles;
      set_count_to_binary(thisctr);
    } else {
      cycles-=(thisctr.count_binary+1);
      thisctr.count_binary-=thisctr.count_binary;
      set_count_to_binary(thisctr);
      decrement(thisctr);
    }
  }
}

void pit_82C54::clock_multiple(Bit8u cnum, Bit32u cycles)
{
  if (cnum>MAX_COUNTER) {
    BX_ERROR(("Counter number too high in clock"));
  } else {
    counter_type &thisctr = counter[cnum];
    while(cycles>0) {
      if (thisctr.next_change_time==0) {
        if (thisctr.count_written) {
          switch(thisctr.mode) {
          case 0:
            if (thisctr.GATE && (thisctr.write_state!=MSByte_multiple)) {
              decrement_multiple(thisctr, cycles);
            }
            break;
          case 1:
            decrement_multiple(thisctr, cycles);
            break;
          case 2:
            if (!thisctr.first_pass && thisctr.GATE) {
              decrement_multiple(thisctr, cycles);
            }
            break;
          case 3:
            if (!thisctr.first_pass && thisctr.GATE) {
              decrement_multiple(thisctr, 2*cycles);
            }
            break;
          case 4:
            if (thisctr.GATE) {
              decrement_multiple(thisctr, cycles);
            }
            break;
          case 5:
            decrement_multiple(thisctr, cycles);
            break;
          default:
            break;
          }
        }
        cycles-=cycles;
      } else {
        switch(thisctr.mode) {
        case 0:
        case 1:
        case 2:
        case 4:
        case 5:
          if (thisctr.next_change_time > cycles) {
            decrement_multiple(thisctr,cycles);
            thisctr.next_change_time-=cycles;
            cycles-=cycles;
          } else {
            decrement_multiple(thisctr,(thisctr.next_change_time-1));
            cycles-=thisctr.next_change_time;
            clock(cnum);
          }
          break;
        case 3:
          if (thisctr.next_change_time > cycles) {
            decrement_multiple(thisctr,cycles*2);
            thisctr.next_change_time-=cycles;
            cycles-=cycles;
          } else {
            decrement_multiple(thisctr,(thisctr.next_change_time-1)*2);
            cycles-=thisctr.next_change_time;
            clock(cnum);
          }
          break;
        default:
          cycles-=cycles;
          break;
        }
      }
    }
#if 0
    print_counter(thisctr);
#endif
  }
}

  void BX_CPP_AttrRegparmN(1)
pit_82C54::clock(Bit8u cnum)
{
    if (cnum>MAX_COUNTER) {
      BX_ERROR(("Counter number too high in clock"));
    } else {
      counter_type &thisctr = counter[cnum];
      switch(thisctr.mode) {
      case 0:
        if (thisctr.count_written) {
          if (thisctr.null_count) {
            set_count(thisctr, thisctr.inlatch);
            if (thisctr.GATE) {
              if (thisctr.count_binary==0) {
                thisctr.next_change_time=1;
              } else {
                thisctr.next_change_time=thisctr.count_binary & 0xFFFF;
              }
            } else {
              thisctr.next_change_time=0;
            }
            thisctr.null_count=0;
          } else {
            if (thisctr.GATE && (thisctr.write_state!=MSByte_multiple)) {
              decrement(thisctr);
              if (!thisctr.OUTpin) {
                thisctr.next_change_time=thisctr.count_binary & 0xFFFF;
                if (!thisctr.count) {
                  set_OUT(thisctr,1);
                }
              } else {
                thisctr.next_change_time=0;
              }
            } else {
              thisctr.next_change_time=0; //if the clock isn't moving.
            }
          }
        } else {
          thisctr.next_change_time=0; //default to 0.
        }
        thisctr.triggerGATE=0;
        break;
      case 1:
        if (thisctr.count_written) {
          if (thisctr.triggerGATE) {
            set_count(thisctr, thisctr.inlatch);
            if (thisctr.count_binary==0) {
              thisctr.next_change_time=1;
            } else {
              thisctr.next_change_time=thisctr.count_binary & 0xFFFF;
            }
            thisctr.null_count=0;
            set_OUT(thisctr,0);
            if (thisctr.write_state==MSByte_multiple) {
              BX_ERROR(("Undefined behavior when loading a half loaded count."));
            }
          } else {
            decrement(thisctr);
            if (!thisctr.OUTpin) {
              if (thisctr.count_binary==0) {
                thisctr.next_change_time=1;
              } else {
                thisctr.next_change_time=thisctr.count_binary & 0xFFFF;
              }
              if (thisctr.count==0) {
                set_OUT(thisctr,1);
              }
            } else {
              thisctr.next_change_time=0;
            }
          }
        } else {
          thisctr.next_change_time=0; //default to 0.
        }
        thisctr.triggerGATE=0;
        break;
      case 2:
        if (thisctr.count_written) {
          if (thisctr.triggerGATE || thisctr.first_pass) {
            set_count(thisctr, thisctr.inlatch);
            thisctr.next_change_time=(thisctr.count_binary-1) & 0xFFFF;
            thisctr.null_count=0;
            if (thisctr.inlatch==1) {
              BX_ERROR(("ERROR: count of 1 is invalid in pit mode 2."));
            }
            if (!thisctr.OUTpin) {
              set_OUT(thisctr,1);
            }
            if (thisctr.write_state==MSByte_multiple) {
              BX_ERROR(("Undefined behavior when loading a half loaded count."));
            }
            thisctr.first_pass=0;
          } else {
            if (thisctr.GATE) {
              decrement(thisctr);
              thisctr.next_change_time=(thisctr.count_binary-1) & 0xFFFF;
              if (thisctr.count==1) {
                thisctr.next_change_time=1;
                set_OUT(thisctr,0);
                thisctr.first_pass=1;
              }
            } else {
              thisctr.next_change_time=0;
            }
          }
        } else {
          thisctr.next_change_time=0;
        }
        thisctr.triggerGATE=0;
        break;
      case 3:
        if (thisctr.count_written) {
          if ((thisctr.triggerGATE || thisctr.first_pass
             || thisctr.state_bit_2) && thisctr.GATE) {
            set_count(thisctr, thisctr.inlatch & 0xFFFE);
            thisctr.state_bit_1=thisctr.inlatch & 0x1;
            if (!thisctr.OUTpin || !thisctr.state_bit_1) {
              if (((thisctr.count_binary/2)-1)==0) {
                thisctr.next_change_time=1;
              } else {
                thisctr.next_change_time=((thisctr.count_binary/2)-1) & 0xFFFF;
              }
            } else {
              if ((thisctr.count_binary/2)==0) {
                thisctr.next_change_time=1;
              } else {
                thisctr.next_change_time=(thisctr.count_binary/2) & 0xFFFF;
              }
            }
            thisctr.null_count=0;
            if (thisctr.inlatch==1) {
              BX_ERROR(("Count of 1 is invalid in pit mode 3."));
            }
            if (!thisctr.OUTpin) {
              set_OUT(thisctr,1);
            } else if (thisctr.OUTpin && !thisctr.first_pass) {
              set_OUT(thisctr,0);
            }
            if (thisctr.write_state==MSByte_multiple) {
              BX_ERROR(("Undefined behavior when loading a half loaded count."));
            }
            thisctr.state_bit_2=0;
            thisctr.first_pass=0;
          } else {
            if (thisctr.GATE) {
              decrement(thisctr);
              decrement(thisctr);
              if (!thisctr.OUTpin || !thisctr.state_bit_1) {
                thisctr.next_change_time=((thisctr.count_binary/2)-1) & 0xFFFF;
              } else {
                thisctr.next_change_time=(thisctr.count_binary/2) & 0xFFFF;
              }
              if (thisctr.count==0) {
                thisctr.state_bit_2=1;
                thisctr.next_change_time=1;
              }
              if ((thisctr.count==2) &&
                 (!thisctr.OUTpin || !thisctr.state_bit_1))
              {
                thisctr.state_bit_2=1;
                thisctr.next_change_time=1;
              }
            } else {
              thisctr.next_change_time=0;
            }
          }
        } else {
          thisctr.next_change_time=0;
        }
        thisctr.triggerGATE=0;
        break;
      case 4:
        if (thisctr.count_written) {
          if (!thisctr.OUTpin) {
            set_OUT(thisctr,1);
          }
          if (thisctr.null_count) {
            set_count(thisctr, thisctr.inlatch);
            if (thisctr.GATE) {
              if (thisctr.count_binary==0) {
                thisctr.next_change_time=1;
              } else {
                thisctr.next_change_time=thisctr.count_binary & 0xFFFF;
              }
            } else {
              thisctr.next_change_time=0;
            }
            thisctr.null_count=0;
            if (thisctr.write_state==MSByte_multiple) {
              BX_ERROR(("Undefined behavior when loading a half loaded count."));
            }
            thisctr.first_pass=1;
          } else {
            if (thisctr.GATE) {
              decrement(thisctr);
              if (thisctr.first_pass) {
                thisctr.next_change_time=thisctr.count_binary & 0xFFFF;
                if (!thisctr.count) {
                  set_OUT(thisctr,0);
                  thisctr.next_change_time=1;
                  thisctr.first_pass=0;
                }
              } else {
                thisctr.next_change_time=0;
              }
            } else {
              thisctr.next_change_time=0;
            }
          }
        } else {
          thisctr.next_change_time=0;
        }
        thisctr.triggerGATE=0;
        break;
      case 5:
        if (thisctr.count_written) {
          if (!thisctr.OUTpin) {
            set_OUT(thisctr,1);
          }
          if (thisctr.triggerGATE) {
            set_count(thisctr, thisctr.inlatch);
            if (thisctr.count_binary==0) {
              thisctr.next_change_time=1;
            } else {
              thisctr.next_change_time=thisctr.count_binary & 0xFFFF;
            }
            thisctr.null_count=0;
            if (thisctr.write_state==MSByte_multiple) {
              BX_ERROR(("Undefined behavior when loading a half loaded count."));
            }
            thisctr.first_pass=1;
          } else {
            decrement(thisctr);
            if (thisctr.first_pass) {
              thisctr.next_change_time=thisctr.count_binary & 0xFFFF;
              if (!thisctr.count) {
                set_OUT(thisctr,0);
                thisctr.next_change_time=1;
                thisctr.first_pass=0;
              }
            } else {
              thisctr.next_change_time=0;
            }
          }
        } else {
          thisctr.next_change_time=0;
        }
        thisctr.triggerGATE=0;
        break;
      default:
        BX_ERROR(("Mode not implemented."));
        thisctr.next_change_time=0;
        thisctr.triggerGATE=0;
        break;
      }
    }
}

void pit_82C54::clock_all(Bit32u cycles)
{
    BX_DEBUG(("clock_all:  cycles=%d",cycles));
    clock_multiple(0,cycles);
    clock_multiple(1,cycles);
    clock_multiple(2,cycles);
}

Bit8u pit_82C54::read(Bit8u address)
{
    if (address>MAX_ADDRESS) {
      BX_ERROR(("Counter address incorrect in data read."));
    } else if (address==CONTROL_ADDRESS) {
      BX_DEBUG(("PIT Read: Control Word Register."));
      //Read from control word register;
      /* This might be okay.  If so, 0 seems the most logical
       *  return value from looking at the docs.
       */
      BX_ERROR(("Read from control word register not defined."));
      return 0;
    } else {
      //Read from a counter;
      BX_DEBUG(("PIT Read: Counter %d.",address));
      counter_type &thisctr=counter[address];
      if (thisctr.status_latched) {
        //Latched Status Read;
        if (thisctr.count_MSB_latched &&
          (thisctr.read_state==MSByte_multiple)) {
          BX_ERROR(("Undefined output when status latched and count half read."));
        } else {
          thisctr.status_latched=0;
          return thisctr.status_latch;
        }
      } else {
        //Latched Count Read;
        if (thisctr.count_LSB_latched) {
          //Read Least Significant Byte;
          if (thisctr.read_state==LSByte_multiple) {
            BX_DEBUG(("Setting read_state to MSB_mult"));
            thisctr.read_state=MSByte_multiple;
          }
          thisctr.count_LSB_latched=0;
          return (thisctr.outlatch & 0xFF);
        } else if (thisctr.count_MSB_latched) {
          //Read Most Significant Byte;
          if (thisctr.read_state==MSByte_multiple) {
            BX_DEBUG(("Setting read_state to LSB_mult"));
            thisctr.read_state=LSByte_multiple;
          }
          thisctr.count_MSB_latched=0;
          return ((thisctr.outlatch>>8) & 0xFF);
        } else {
          //Unlatched Count Read;
          if (!(thisctr.read_state & 0x1)) {
            //Read Least Significant Byte;
            if (thisctr.read_state==LSByte_multiple) {
              thisctr.read_state=MSByte_multiple;
              BX_DEBUG(("Setting read_state to MSB_mult"));
            }
            return (thisctr.count & 0xFF);
          } else {
            //Read Most Significant Byte;
            if (thisctr.read_state==MSByte_multiple) {
              BX_DEBUG(("Setting read_state to LSB_mult"));
              thisctr.read_state=LSByte_multiple;
            }
            return ((thisctr.count>>8) & 0xFF);
          }
        }
      }
    }

    //Should only get here on errors;
    return 0;
}

void pit_82C54::write(Bit8u address, Bit8u data)
{
    if (address>MAX_ADDRESS) {
      BX_ERROR(("Counter address incorrect in data write."));
    } else if (address==CONTROL_ADDRESS) {
      Bit8u SC, RW, M, BCD;
      controlword=data;
      BX_DEBUG(("Control Word Write."));
      SC = (controlword>>6) & 0x3;
      RW = (controlword>>4) & 0x3;
      M = (controlword>>1) & 0x7;
      BCD = controlword & 0x1;
      if (SC == 3) {
        //READ_BACK command;
        int i;
        BX_DEBUG(("READ_BACK command."));
        for(i=0;i<=MAX_COUNTER;i++) {
          if ((M>>i) & 0x1) {
            //If we are using this counter;
            counter_type &thisctr=counter[i];
            if (!((controlword>>5) & 1)) {
              //Latch Count;
              latch_counter(thisctr);
            }
            if (!((controlword>>4) & 1)) {
              //Latch Status;
              if (thisctr.status_latched) {
                //Do nothing because latched status has not been read.;
              } else {
                thisctr.status_latch=
                  ((thisctr.OUTpin & 0x1) << 7) |
                  ((thisctr.null_count & 0x1) << 6) |
                  ((thisctr.rw_mode & 0x3) << 4) |
                  ((thisctr.mode & 0x7) << 1) |
                  (thisctr.bcd_mode&0x1);
                thisctr.status_latched=1;
              }
            }
          }
        }
      } else {
        counter_type &thisctr = counter[SC];
        if (!RW) {
          //Counter Latch command;
          BX_DEBUG(("Counter Latch command.  SC=%d",SC));
          latch_counter(thisctr);
        } else {
          //Counter Program Command;
          BX_DEBUG(("Counter Program command.  SC=%d, RW=%d, M=%d, BCD=%d",SC,RW,M,BCD));
          thisctr.null_count=1;
          thisctr.count_LSB_latched=0;
          thisctr.count_MSB_latched=0;
          thisctr.status_latched=0;
          thisctr.inlatch=0;
          thisctr.count_written=0;
          thisctr.first_pass=1;
          thisctr.rw_mode=RW;
          thisctr.bcd_mode=(BCD > 0);
          thisctr.mode=M;
          switch(RW) {
          case 0x1:
            BX_DEBUG(("Setting read_state to LSB"));
            thisctr.read_state=LSByte;
            thisctr.write_state=LSByte;
            break;
          case 0x2:
            BX_DEBUG(("Setting read_state to MSB"));
            thisctr.read_state=MSByte;
            thisctr.write_state=MSByte;
            break;
          case 0x3:
            BX_DEBUG(("Setting read_state to LSB_mult"));
            thisctr.read_state=LSByte_multiple;
            thisctr.write_state=LSByte_multiple;
            break;
          default:
            BX_ERROR(("RW field invalid in control word write."));
            break;
          }
          //All modes except mode 0 have initial output of 1.;
          if (M) {
            set_OUT(thisctr, 1);
          } else {
            set_OUT(thisctr, 0);
          }
          thisctr.next_change_time=0;
        }
      }
    } else {
      //Write to counter initial value.
      counter_type &thisctr = counter[address];
      BX_DEBUG(("Write Initial Count: counter=%d, count=%d",address,data));
      switch(thisctr.write_state) {
      case LSByte_multiple:
        thisctr.inlatch=(thisctr.inlatch & (0xFF<<8)) | data;
        thisctr.write_state=MSByte_multiple;
        break;
      case LSByte:
        thisctr.inlatch=(thisctr.inlatch & (0xFF<<8)) | data;
        thisctr.null_count=1;
        thisctr.count_written=1;
        break;
      case MSByte_multiple:
        thisctr.write_state=LSByte_multiple;
      case MSByte: //shared between MSB_multiple and MSByte
        thisctr.inlatch=(thisctr.inlatch & 0xFF) | (data<<8);
        thisctr.null_count=1;
        thisctr.count_written=1;
        break;
      default:
        BX_ERROR(("write counter in invalid write state."));
        break;
      }
      switch(thisctr.mode) {
      case 0:
        if (thisctr.write_state==MSByte_multiple) {
          set_OUT(thisctr,0);
        }
        thisctr.next_change_time=1;
        break;
      case 1:
        if (thisctr.triggerGATE) { //for initial writes, if already saw trigger.
          thisctr.next_change_time=1;
        } //Otherwise, no change.
        break;
      case 6:
      case 2:
        thisctr.next_change_time=1; //FIXME: this could be loosened.
        break;
      case 7:
      case 3:
        thisctr.next_change_time=1; //FIXME: this could be loosened.
        break;
      case 4:
        thisctr.next_change_time=1;
        break;
      case 5:
        if (thisctr.triggerGATE) { //for initial writes, if already saw trigger.
          thisctr.next_change_time=1;
        } //Otherwise, no change.
        break;
      }
    }
}

void pit_82C54::set_GATE(Bit8u cnum, bx_bool data)
{
  if (cnum>MAX_COUNTER) {
    BX_ERROR(("Counter number incorrect in 82C54 set_GATE"));
  } else {
    counter_type &thisctr = counter[cnum];
    if (!((thisctr.GATE&&data) || (!(thisctr.GATE||data)))) {
      BX_INFO(("Changing GATE %d to: %d",cnum,data));
      thisctr.GATE=data;
      if (thisctr.GATE) {
        thisctr.triggerGATE=1;
      }
      switch(thisctr.mode) {
        case 0:
          if (data && thisctr.count_written) {
            if (thisctr.null_count) {
              thisctr.next_change_time=1;
            } else {
              if ((!thisctr.OUTpin) &&
                   (thisctr.write_state!=MSByte_multiple))
              {
                if (thisctr.count_binary==0) {
                  thisctr.next_change_time=1;
                } else {
                  thisctr.next_change_time=thisctr.count_binary & 0xFFFF;
                }
              } else {
                thisctr.next_change_time=0;
              }
            }
          } else {
            if (thisctr.null_count) {
              thisctr.next_change_time=1;
            } else {
              thisctr.next_change_time=0;
            }
          }
          break;
        case 1:
          if (data && thisctr.count_written) { //only triggers cause a change.
            thisctr.next_change_time=1;
          }
          break;
        case 2:
          if (!data) {
            set_OUT(thisctr,1);
            thisctr.next_change_time=0;
          } else {
            if (thisctr.count_written) {
              thisctr.next_change_time=1;
            } else {
              thisctr.next_change_time=0;
            }
          }
          break;
        case 3:
          if (!data) {
            set_OUT(thisctr,1);
            thisctr.first_pass=1;
            thisctr.next_change_time=0;
          } else {
            if (thisctr.count_written) {
              thisctr.next_change_time=1;
            } else {
              thisctr.next_change_time=0;
            }
          }
          break;
        case 4:
          if (!thisctr.OUTpin || thisctr.null_count) {
            thisctr.next_change_time=1;
          } else {
            if (data && thisctr.count_written) {
              if (thisctr.first_pass) {
                if (thisctr.count_binary==0) {
                  thisctr.next_change_time=1;
                } else {
                  thisctr.next_change_time=thisctr.count_binary & 0xFFFF;
                }
              } else {
                thisctr.next_change_time=0;
              }
            } else {
              thisctr.next_change_time=0;
            }
          }
          break;
        case 5:
          if (data && thisctr.count_written) { //only triggers cause a change.
            thisctr.next_change_time=1;
          }
          break;
        default:
          break;
      }
    }
  }
}

bx_bool pit_82C54::read_OUT(Bit8u cnum)
{
  if (cnum>MAX_COUNTER) {
    BX_ERROR(("Counter number incorrect in 82C54 read_OUT"));
    return 0;
  }

  return counter[cnum].OUTpin;
}

bx_bool pit_82C54::read_GATE(Bit8u cnum)
{
  if (cnum>MAX_COUNTER) {
    BX_ERROR(("Counter number incorrect in 82C54 read_GATE"));
    return 0;
  }

  return counter[cnum].GATE;
}

Bit32u pit_82C54::get_clock_event_time(Bit8u cnum)
{
  if (cnum>MAX_COUNTER) {
    BX_ERROR(("Counter number incorrect in 82C54 read_GATE"));
    return 0;
  }

  return counter[cnum].next_change_time;
}

Bit32u pit_82C54::get_next_event_time(void)
{
  Bit32u time0=get_clock_event_time(0);
  Bit32u time1=get_clock_event_time(1);
  Bit32u time2=get_clock_event_time(2);

  Bit32u out=time0;
  if (time1 && (time1<out))
    out=time1;
  if (time2 && (time2<out))
    out=time2;
  return out;
}

Bit16u pit_82C54::get_inlatch(int counternum)
{
  return counter[counternum].inlatch;
}

void pit_82C54::set_OUT_handler(Bit8u counternum, out_handler_t outh)
{
  counter[counternum].out_handler = outh;
}