/*
 *  © 2021 Neil McKechnie
 *  © 2021 Mike S
 *  © 2021 Fred Decker
 *  © 2021 Herb Morton
 *  © 2020-2022 Harald Barth
 *  © 2020-2021 M Steve Todd
 *  © 2020-2021 Chris Harlow
 *  All rights reserved.
 *
 *  This file is part of Asbelos DCC API
 *
 *  This 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.
 *
 *  It 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 CommandStation.  If not, see <https://www.gnu.org/licenses/>.
 */
#include "DIAG.h"
#include "DCC.h"
#include "DCCWaveform.h"
#ifndef DISABLE_EEPROM
#include "EEStore.h"
#endif
#include "GITHUB_SHA.h"
#include "version.h"
#include "FSH.h"
#include "IODevice.h"
#include "EXRAIL2.h"
#include "CommandDistributor.h"
#include "TrackManager.h"
#include "DCCTimer.h"

// This module is responsible for converting API calls into
// messages to be sent to the waveform generator.
// It has no visibility of the hardware, timers, interrupts
// nor of the waveform issues such as preambles, start bits checksums or cutouts.
//
// Nor should it have to deal with JMRI responsess other than the OK/FAIL
// or cv value returned. I will move that back to the JMRI interface later
//
// The interface to the waveform generator is narrowed down to merely:
//   Scheduling a message on the prog or main track using a function
//   Obtaining ACKs from the prog track using a function
//   There are no volatiles here.

const byte FN_GROUP_1=0x01;
const byte FN_GROUP_2=0x02;
const byte FN_GROUP_3=0x04;
const byte FN_GROUP_4=0x08;
const byte FN_GROUP_5=0x10;

FSH* DCC::shieldName=NULL;
byte DCC::globalSpeedsteps=128;

void DCC::begin(const FSH * motorShieldName) {
  shieldName=(FSH *)motorShieldName;
#if defined(ARDUINO_ARCH_SAMD)
  StringFormatter::send(SerialUSB,F("<iDCC-EX V-%S / %S / %S G-%S>\n"), F(VERSION), F(ARDUINO_TYPE), shieldName, F(GITHUB_SHA));
#else
  StringFormatter::send(Serial,F("<iDCC-EX V-%S / %S / %S G-%S>\n"), F(VERSION), F(ARDUINO_TYPE), shieldName, F(GITHUB_SHA));
#endif

#ifndef DISABLE_EEPROM
  // Load stuff from EEprom
  (void)EEPROM; // tell compiler not to warn this is unused
  EEStore::init();
#endif

  DCCWaveform::begin();
}


void DCC::setThrottle( uint16_t cab, uint8_t tSpeed, bool tDirection)  {
  byte speedCode = (tSpeed & 0x7F)  + tDirection * 128;
  setThrottle2(cab, speedCode);
  TrackManager::setDCSignal(cab,speedCode); // in case this is a dcc track on this addr
  // retain speed for loco reminders
  updateLocoReminder(cab, speedCode );
}

void DCC::setThrottle2( uint16_t cab, byte speedCode)  {

  uint8_t b[4];
  uint8_t nB = 0;
  // DIAG(F("setSpeedInternal %d %x"),cab,speedCode);

  if (cab > HIGHEST_SHORT_ADDR)
    b[nB++] = highByte(cab) | 0xC0;    // convert train number into a two-byte address
  b[nB++] = lowByte(cab);

  if (globalSpeedsteps <= 28) {

    uint8_t speed128 = speedCode & 0x7F;
    uint8_t speed28;
    uint8_t code28;

    if (speed128 == 0 || speed128 == 1) { // stop or emergency stop
      code28 = speed128;
    } else {
      speed28= (speed128*10+36)/46;                 // convert 2-127 to 1-28
/*
      if (globalSpeedsteps <= 14)                   // Don't want to do 14 steps, to get F0 there is ugly
        code28 = (speed28+3)/2 | (Value of F0);     // convert 1-28 to DCC 14 step speed code
      else
*/
      code28 = (speed28+3)/2 | ( (speed28 & 1) ? 0 : 0b00010000 ); // convert 1-28 to DCC 28 step speed code
    }
    //        Construct command byte from:
    //        command      speed    direction
    b[nB++] = 0b01000000 | code28 | ((speedCode & 0x80) ? 0b00100000 : 0);

  } else { // 128 speedsteps

    b[nB++] = SET_SPEED;                      // 128-step speed control byte
    b[nB++] = speedCode; // for encoding see setThrottle

  }

  DCCWaveform::mainTrack.schedulePacket(b, nB, 0);
}

void DCC::setFunctionInternal(int cab, byte byte1, byte byte2) {
  // DIAG(F("setFunctionInternal %d %x %x"),cab,byte1,byte2);
  byte b[4];
  byte nB = 0;

  if (cab > HIGHEST_SHORT_ADDR)
    b[nB++] = highByte(cab) | 0xC0;    // convert train number into a two-byte address
  b[nB++] = lowByte(cab);
  if (byte1!=0) b[nB++] = byte1;
  b[nB++] = byte2;

  DCCWaveform::mainTrack.schedulePacket(b, nB, 0);
}

uint8_t DCC::getThrottleSpeed(int cab) {
  int reg=lookupSpeedTable(cab);
  if (reg<0) return -1;
  return speedTable[reg].speedCode & 0x7F;
}

bool DCC::getThrottleDirection(int cab) {
  int reg=lookupSpeedTable(cab);
  if (reg<0) return true;
  return (speedTable[reg].speedCode & 0x80) !=0;
}

// Set function to value on or off
void DCC::setFn( int cab, int16_t functionNumber, bool on) {
  if (cab<=0 ) return;

  if (functionNumber>28) {
    //non reminding advanced binary bit set
    byte b[5];
    byte nB = 0;
    if (cab > HIGHEST_SHORT_ADDR)
      b[nB++] = highByte(cab) | 0xC0;    // convert train number into a two-byte address
    b[nB++] = lowByte(cab);
    if (functionNumber <= 127) {
       b[nB++] = 0b11011101;   // Binary State Control Instruction short form
       b[nB++] = functionNumber | (on ? 0x80 : 0);
    }
    else  {
       b[nB++] = 0b11000000;   // Binary State Control Instruction long form
       b[nB++] = (functionNumber & 0x7F) | (on ? 0x80 : 0);  // low order bits and state flag
       b[nB++] = functionNumber >>7 ;  // high order bits
    }
    DCCWaveform::mainTrack.schedulePacket(b, nB, 4);
    return;
  }

  int reg = lookupSpeedTable(cab);
  if (reg<0) return;

  // Take care of functions:
  // Set state of function
  unsigned long previous=speedTable[reg].functions;
  unsigned long funcmask = (1UL<<functionNumber);
  if (on) {
      speedTable[reg].functions |= funcmask;
  } else {
      speedTable[reg].functions &= ~funcmask;
  }
  if (speedTable[reg].functions != previous) {
    updateGroupflags(speedTable[reg].groupFlags, functionNumber);
    CommandDistributor::broadcastLoco(reg);
  }
}

// Flip function state
void DCC::changeFn( int cab, int16_t functionNumber) {
  if (cab<=0 || functionNumber>28) return;
  int reg = lookupSpeedTable(cab);
  if (reg<0) return;
  unsigned long funcmask = (1UL<<functionNumber);
  speedTable[reg].functions ^= funcmask;
  updateGroupflags(speedTable[reg].groupFlags, functionNumber);
  CommandDistributor::broadcastLoco(reg);
}

int DCC::getFn( int cab, int16_t functionNumber) {
  if (cab<=0 || functionNumber>28) return -1;  // unknown
  int reg = lookupSpeedTable(cab);
  if (reg<0) return -1;

  unsigned long funcmask = (1UL<<functionNumber);
  return  (speedTable[reg].functions & funcmask)? 1 : 0;
}

// Set the group flag to say we have touched the particular group.
// A group will be reminded only if it has been touched.
void DCC::updateGroupflags(byte & flags, int16_t functionNumber) {
  byte groupMask;
  if (functionNumber<=4)       groupMask=FN_GROUP_1;
  else if (functionNumber<=8)  groupMask=FN_GROUP_2;
  else if (functionNumber<=12) groupMask=FN_GROUP_3;
  else if (functionNumber<=20) groupMask=FN_GROUP_4;
  else                         groupMask=FN_GROUP_5;
  flags |= groupMask;
}

uint32_t DCC::getFunctionMap(int cab) {
  if (cab<=0) return 0;  // unknown pretend all functions off
  int reg = lookupSpeedTable(cab);
  return (reg<0)?0:speedTable[reg].functions;
}

void DCC::setAccessory(int address, byte number, bool activate) {
  #ifdef DIAG_IO
  DIAG(F("DCC::setAccessory(%d,%d,%d)"), address, number, activate);
  #endif
  // use masks to detect wrong values and do nothing
  if(address != (address & 511))
    return;
  if(number != (number & 3))
    return;
  byte b[2];

  b[0] = address % 64 + 128;                                     // first byte is of the form 10AAAAAA, where AAAAAA represent 6 least signifcant bits of accessory address
  b[1] = ((((address / 64) % 8) << 4) + (number % 4 << 1) + activate % 2) ^ 0xF8; // second byte is of the form 1AAACDDD, where C should be 1, and the least significant D represent activate/deactivate

  DCCWaveform::mainTrack.schedulePacket(b, 2, 4);      // Repeat the packet four times
#if defined(EXRAIL_ACTIVE)
  RMFT2::activateEvent(address<<2|number,activate);
#endif
}

//
// writeCVByteMain: Write a byte with PoM on main. This writes
// the 5 byte sized packet to implement this DCC function
//
void DCC::writeCVByteMain(int cab, int cv, byte bValue)  {
  byte b[5];
  byte nB = 0;
  if (cab > HIGHEST_SHORT_ADDR)
    b[nB++] = highByte(cab) | 0xC0;    // convert train number into a two-byte address

  b[nB++] = lowByte(cab);
  b[nB++] = cv1(WRITE_BYTE_MAIN, cv); // any CV>1023 will become modulus(1024) due to bit-mask of 0x03
  b[nB++] = cv2(cv);
  b[nB++] = bValue;

  DCCWaveform::mainTrack.schedulePacket(b, nB, 4);
}

//
// writeCVBitMain: Write a bit of a byte with PoM on main. This writes
// the 5 byte sized packet to implement this DCC function
//
void DCC::writeCVBitMain(int cab, int cv, byte bNum, bool bValue)  {
  byte b[5];
  byte nB = 0;
  bValue = bValue % 2;
  bNum = bNum % 8;

  if (cab > HIGHEST_SHORT_ADDR)
    b[nB++] = highByte(cab) | 0xC0;    // convert train number into a two-byte address

  b[nB++] = lowByte(cab);
  b[nB++] = cv1(WRITE_BIT_MAIN, cv); // any CV>1023 will become modulus(1024) due to bit-mask of 0x03
  b[nB++] = cv2(cv);
  b[nB++] = WRITE_BIT | (bValue ? BIT_ON : BIT_OFF) | bNum;

  DCCWaveform::mainTrack.schedulePacket(b, nB, 4);
}

FSH* DCC::getMotorShieldName() {
  return shieldName;
}

const ackOp FLASH WRITE_BIT0_PROG[] = {
     BASELINE,
     W0,WACK,
     V0, WACK,  // validate bit is 0
     ITC1,      // if acked, callback(1)
     CALLFAIL  // callback (-1)
};
const ackOp FLASH WRITE_BIT1_PROG[] = {
     BASELINE,
     W1,WACK,
     V1, WACK,  // validate bit is 1
     ITC1,      // if acked, callback(1)
     CALLFAIL  // callback (-1)
};

const ackOp FLASH VERIFY_BIT0_PROG[] = {
     BASELINE,
     V0, WACK,  // validate bit is 0
     ITC0,      // if acked, callback(0)
     V1, WACK,  // validate bit is 1
     ITC1,
     CALLFAIL  // callback (-1)
};
const ackOp FLASH VERIFY_BIT1_PROG[] = {
     BASELINE,
     V1, WACK,  // validate bit is 1
     ITC1,      // if acked, callback(1)
     V0, WACK,
     ITC0,
     CALLFAIL  // callback (-1)
};

const ackOp FLASH READ_BIT_PROG[] = {
     BASELINE,
     V1, WACK,  // validate bit is 1
     ITC1,      // if acked, callback(1)
     V0, WACK,  // validate bit is zero
     ITC0,      // if acked callback 0
     CALLFAIL       // bit not readable
     };

const ackOp FLASH WRITE_BYTE_PROG[] = {
      BASELINE,
      WB,WACK,ITC1,    // Write and callback(1) if ACK
      // handle decoders that dont ack a write
      VB,WACK,ITC1,    // validate byte and callback(1) if correct
      CALLFAIL        // callback (-1)
      };

const ackOp FLASH VERIFY_BYTE_PROG[] = {
      BASELINE,
      BIV,         // ackManagerByte initial value
      VB,WACK,     // validate byte
      ITCB,       // if ok callback value	
      STARTMERGE,    //clear bit and byte values ready for merge pass
      // each bit is validated against 0 and the result inverted in MERGE
      // this is because there tend to be more zeros in cv values than ones.
      // There is no need for one validation as entire byte is validated at the end
      V0, WACK, MERGE,        // read and merge first tested bit (7)
      ITSKIP,                 // do small excursion if there was no ack
        SETBIT,(ackOp)7,
        V1, WACK, NAKFAIL,    // test if there is an ack on the inverse of this bit (7)
        SETBIT,(ackOp)6,      // and abort whole test if not else continue with bit (6)
      SKIPTARGET,
      V0, WACK, MERGE,        // read and merge second tested bit (6)
      V0, WACK, MERGE,        // read and merge third  tested bit (5) ...
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      VB, WACK, ITCBV,  // verify merged byte and return it if acked ok - with retry report
      CALLFAIL };


const ackOp FLASH READ_CV_PROG[] = {
      BASELINE,
      STARTMERGE,    //clear bit and byte values ready for merge pass
      // each bit is validated against 0 and the result inverted in MERGE
      // this is because there tend to be more zeros in cv values than ones.
      // There is no need for one validation as entire byte is validated at the end
      V0, WACK, MERGE,        // read and merge first tested bit (7)
      ITSKIP,                 // do small excursion if there was no ack
        SETBIT,(ackOp)7,
        V1, WACK, NAKFAIL,    // test if there is an ack on the inverse of this bit (7)
        SETBIT,(ackOp)6,      // and abort whole test if not else continue with bit (6)
      SKIPTARGET,
      V0, WACK, MERGE,        // read and merge second tested bit (6)
      V0, WACK, MERGE,        // read and merge third  tested bit (5) ...
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      VB, WACK, ITCB,  // verify merged byte and return it if acked ok
      CALLFAIL };          // verification failed


const ackOp FLASH LOCO_ID_PROG[] = {
      BASELINE,
      SETCV, (ackOp)19,     // CV 19 is consist setting
      SETBYTE, (ackOp)0,
      VB, WACK, ITSKIP,     // ignore consist if cv19 is zero (no consist)
      SETBYTE, (ackOp)128,
      VB, WACK, ITSKIP,     // ignore consist if cv19 is 128 (no consist, direction bit set)
      STARTMERGE,           // Setup to read cv 19
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      VB, WACK, ITCB7,  // return 7 bits only, No_ACK means CV19 not supported so ignore it

      SKIPTARGET,     // continue here if CV 19 is zero or fails all validation
      SETCV,(ackOp)29,
      SETBIT,(ackOp)5,
      V0, WACK, ITSKIP,  // Skip to SKIPTARGET if bit 5 of CV29 is zero

      // Long locoid
      SETCV, (ackOp)17,       // CV 17 is part of locoid
      STARTMERGE,
      V0, WACK, MERGE,  // read and merge bit 1 etc
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      VB, WACK, NAKFAIL,  // verify merged byte and return -1 it if not acked ok
      STASHLOCOID,         // keep stashed cv 17 for later
      // Read 2nd part from CV 18
      SETCV, (ackOp)18,
      STARTMERGE,
      V0, WACK, MERGE,  // read and merge bit 1 etc
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      VB, WACK, NAKFAIL,  // verify merged byte and return -1 it if not acked ok
      COMBINELOCOID,        // Combile byte with stash to make long locoid and callback

      // ITSKIP Skips to here if CV 29 bit 5 was zero. so read CV 1 and return that
      SKIPTARGET,
      SETCV, (ackOp)1,
      STARTMERGE,
      SETBIT, (ackOp)6,  // skip over first bit as we know its a zero
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      V0, WACK, MERGE,
      VB, WACK, ITCB,  // verify merged byte and callback
      CALLFAIL
      };

const ackOp FLASH SHORT_LOCO_ID_PROG[] = {
      BASELINE,
      SETCV,(ackOp)19,
      SETBYTE, (ackOp)0,
      WB,WACK,     // ignore dedcoder without cv19 support
      // Turn off long address flag
      SETCV,(ackOp)29,
      SETBIT,(ackOp)5,
      W0,WACK,
      V0,WACK,NAKFAIL,
      SETCV, (ackOp)1,
      SETBYTEL,   // low byte of word
      WB,WACK,    // some decoders don't ACK writes
      VB,WACK,ITCB,
      CALLFAIL
};

const ackOp FLASH LONG_LOCO_ID_PROG[] = {
      BASELINE,
      // Clear consist CV 19
      SETCV,(ackOp)19,
      SETBYTE, (ackOp)0,
      WB,WACK,     // ignore decoder without cv19 support
      // Turn on long address flag cv29 bit 5
      SETCV,(ackOp)29,
      SETBIT,(ackOp)5,
      W1,WACK,
      V1,WACK,NAKFAIL,
      // Store high byte of address in cv 17
      SETCV, (ackOp)17,
      SETBYTEH,   // high byte of word
      WB,WACK,
      VB,WACK,NAKFAIL,
      // store
      SETCV, (ackOp)18,
      SETBYTEL,   // low byte of word
      WB,WACK,
      VB,WACK,ITC1,   // callback(1) means Ok
      CALLFAIL
};

void  DCC::writeCVByte(int16_t cv, byte byteValue, ACK_CALLBACK callback)  {
  DCCACK::Setup(cv, byteValue,  WRITE_BYTE_PROG, callback);
}

void DCC::writeCVBit(int16_t cv, byte bitNum, bool bitValue, ACK_CALLBACK callback)  {
  if (bitNum >= 8) callback(-1);
  else DCCACK::Setup(cv, bitNum, bitValue?WRITE_BIT1_PROG:WRITE_BIT0_PROG, callback);
}

void  DCC::verifyCVByte(int16_t cv, byte byteValue, ACK_CALLBACK callback)  {
  DCCACK::Setup(cv, byteValue,  VERIFY_BYTE_PROG, callback);
}

void DCC::verifyCVBit(int16_t cv, byte bitNum, bool bitValue, ACK_CALLBACK callback)  {
  if (bitNum >= 8) callback(-1);
  else DCCACK::Setup(cv, bitNum, bitValue?VERIFY_BIT1_PROG:VERIFY_BIT0_PROG, callback);
}


void DCC::readCVBit(int16_t cv, byte bitNum, ACK_CALLBACK callback)  {
  if (bitNum >= 8) callback(-1);
  else DCCACK::Setup(cv, bitNum,READ_BIT_PROG, callback);
}

void DCC::readCV(int16_t cv, ACK_CALLBACK callback)  {
  DCCACK::Setup(cv, 0,READ_CV_PROG, callback);
}

void DCC::getLocoId(ACK_CALLBACK callback) {
  DCCACK::Setup(0,0, LOCO_ID_PROG, callback);
}

void DCC::setLocoId(int id,ACK_CALLBACK callback) {
  if (id<1 || id>10239) { //0x27FF according to standard
    callback(-1);
    return;
  }
  if (id<=HIGHEST_SHORT_ADDR)
      DCCACK::Setup(id, SHORT_LOCO_ID_PROG, callback);
  else
      DCCACK::Setup(id | 0xc000,LONG_LOCO_ID_PROG, callback);
}

void DCC::forgetLoco(int cab) {  // removes any speed reminders for this loco
  setThrottle2(cab,1); // ESTOP this loco if still on track
  int reg=lookupSpeedTable(cab);
  if (reg>=0) speedTable[reg].loco=0;
  setThrottle2(cab,1); // ESTOP if this loco still on track
}
void DCC::forgetAllLocos() {  // removes all speed reminders
  setThrottle2(0,1); // ESTOP all locos still on track
  for (int i=0;i<MAX_LOCOS;i++) speedTable[i].loco=0;
}

byte DCC::loopStatus=0;

void DCC::loop()  {
  TrackManager::loop(); // power overload checks
  issueReminders();
}

void DCC::issueReminders() {
  // if the main track transmitter still has a pending packet, skip this time around.
  if ( DCCWaveform::mainTrack.packetPending) return;

  // This loop searches for a loco in the speed table starting at nextLoco and cycling back around
  for (int reg=0;reg<MAX_LOCOS;reg++) {
       int slot=reg+nextLoco;
       if (slot>=MAX_LOCOS) slot-=MAX_LOCOS;
       if (speedTable[slot].loco > 0) {
          // have found the next loco to remind
          // issueReminder will return true if this loco is completed (ie speed and functions)
          if (issueReminder(slot)) nextLoco=slot+1;
          return;
        }
  }
}

bool DCC::issueReminder(int reg) {
  unsigned long functions=speedTable[reg].functions;
  int loco=speedTable[reg].loco;
  byte flags=speedTable[reg].groupFlags;

  switch (loopStatus) {
        case 0:
      //   DIAG(F("Reminder %d speed %d"),loco,speedTable[reg].speedCode);
         setThrottle2(loco, speedTable[reg].speedCode);
         break;
       case 1: // remind function group 1 (F0-F4)
          if (flags & FN_GROUP_1)
              setFunctionInternal(loco,0, 128 | ((functions>>1)& 0x0F) | ((functions & 0x01)<<4)); // 100D DDDD
          break;
       case 2: // remind function group 2 F5-F8
          if (flags & FN_GROUP_2)
              setFunctionInternal(loco,0, 176 | ((functions>>5)& 0x0F));                           // 1011 DDDD
          break;
       case 3: // remind function group 3 F9-F12
          if (flags & FN_GROUP_3)
              setFunctionInternal(loco,0, 160 | ((functions>>9)& 0x0F));                           // 1010 DDDD
          break;
       case 4: // remind function group 4 F13-F20
          if (flags & FN_GROUP_4)
              setFunctionInternal(loco,222, ((functions>>13)& 0xFF));
          flags&= ~FN_GROUP_4;  // dont send them again
          break;
       case 5: // remind function group 5 F21-F28
          if (flags & FN_GROUP_5)
              setFunctionInternal(loco,223, ((functions>>21)& 0xFF));
          flags&= ~FN_GROUP_5;  // dont send them again
          break;
      }
      loopStatus++;
      // if we reach status 6 then this loco is done so
      // reset status to 0 for next loco and return true so caller
      // moves on to next loco.
      if (loopStatus>5) loopStatus=0;
      return loopStatus==0;
    }




///// Private helper functions below here /////////////////////

byte DCC::cv1(byte opcode, int cv)  {
  cv--;
  return (highByte(cv) & (byte)0x03) | opcode;
}
byte DCC::cv2(int cv)  {
  cv--;
  return lowByte(cv);
}

int DCC::lookupSpeedTable(int locoId, bool autoCreate) {
  // determine speed reg for this loco
  int firstEmpty = MAX_LOCOS;
  int reg;
  for (reg = 0; reg < MAX_LOCOS; reg++) {
    if (speedTable[reg].loco == locoId) break;
    if (speedTable[reg].loco == 0 && firstEmpty == MAX_LOCOS) firstEmpty = reg;
  }

  // return -1 if not found and not auto creating
  if (reg== MAX_LOCOS && !autoCreate) return -1; 
  if (reg == MAX_LOCOS) reg = firstEmpty;
  if (reg >= MAX_LOCOS) {
    DIAG(F("Too many locos"));
    return -1;
  }
  if (reg==firstEmpty){
        speedTable[reg].loco = locoId;
        speedTable[reg].speedCode=128;  // default direction forward
        speedTable[reg].groupFlags=0;
        speedTable[reg].functions=0;
  }
  return reg;
}

void  DCC::updateLocoReminder(int loco, byte speedCode) {

  if (loco==0) {
     // broadcast stop/estop but dont change direction
     for (int reg = 0; reg < MAX_LOCOS; reg++) {
       if (speedTable[reg].loco==0) continue;
       byte newspeed=(speedTable[reg].speedCode & 0x80) |  (speedCode & 0x7f);
       if (speedTable[reg].speedCode != newspeed) {
         speedTable[reg].speedCode = newspeed;
         CommandDistributor::broadcastLoco(reg);
       }
     }
     return;
  }

  // determine speed reg for this loco
  int reg=lookupSpeedTable(loco);
  if (reg>=0 && speedTable[reg].speedCode!=speedCode) {
    speedTable[reg].speedCode = speedCode;
    CommandDistributor::broadcastLoco(reg);
  }
}

DCC::LOCO DCC::speedTable[MAX_LOCOS];
int DCC::nextLoco = 0;


void DCC::displayCabList(Print * stream) {

    int used=0;
    for (int reg = 0; reg < MAX_LOCOS; reg++) {
       if (speedTable[reg].loco>0) {
        used ++;
        StringFormatter::send(stream,F("cab=%d, speed=%d, dir=%c \n"),
           speedTable[reg].loco,  speedTable[reg].speedCode & 0x7f,(speedTable[reg].speedCode & 0x80) ? 'F':'R');
       }
     }
     StringFormatter::send(stream,F("Used=%d, max=%d\n"),used,MAX_LOCOS);

}