DynamixelProtocol.h

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//-*-c++-*-
#ifndef INCLUDED_DynamixelProtocol_h_
#define INCLUDED_DynamixelProtocol_h_

#include "IPC/Thread.h"
#include "Shared/debuget.h"
#include <cstddef>
#include <iostream>
#include <map>
#include <string>

//! Contains structures which define the layout of the binary communication with Dynamixel servos
namespace DynamixelProtocol {
  
  const unsigned int MAX_ID=0xFD;
  const unsigned int BROADCAST_ID=0xFE;
  const unsigned int INVALID_ID=0xFF;
  const unsigned int MARKER_VALUE=0xFF;
  
  extern const char* MODEL_UNKNOWN_NAME;
  enum ModelID_t {
    MODEL_DX113=113,
    MODEL_DX116=116,
    MODEL_DX117=117,
    MODEL_AX12=12,
    MODEL_AX18=18,
    MODEL_AXS1=13,
    MODEL_RX10=10,
    MODEL_RX24=24,
    MODEL_RX28=28,
    MODEL_RX64=64,
    MODEL_EX106P=107,
    MODEL_UNKNOWN=static_cast<size_t>(1<<16)
  };
  //! maps model numbers (e.g. from a ServoInfoResponse) to human-readable names
  extern const std::map<DynamixelProtocol::ModelID_t, const std::string> dynamixelModels;
  
  //! symbol names for status response level settings, see SetStatusResponseLevelCmd
  enum StatusResponseLevel {
    RESPOND_NONE=0, //!< don't respond to anything
    RESPOND_READ=1, //!< only respond to read commands (see ReadCmd and GenericResponseHeader subclasses)
    RESPOND_ALL=2 //!< send a response packet for every command (see WriteResponse)
  };
  
  //! Compute a bitwise-negated checksum for a region of memory, with an optional offset
  /*! You can add checksums from multiple calls to this function, then bitwise-negate at the
  *  end to obtain final checksum value */
  inline unsigned char nchecksum(const unsigned char* p, size_t len, size_t off=0) {
    const unsigned char* end=p+len;
    p+=off;
    unsigned char c=0;
    while(p!=end) {
      //debuget::charhexout(*p); cout << ' '; debuget::charhexout(c+*p); cout << endl;
      c+=*p++;
    }
    return c;
  }
  //! 'specialization' of nchecksum for the GenericCmdHeader, which should skip marker fields
  inline unsigned char nchecksum(const struct GenericCmdHeader& p, size_t len);
  //! 'specialization' of nchecksum for the GenericResponseHeader, which should skip marker fields
  inline unsigned char nchecksum(const struct GenericResponseHeader& p, size_t len);
  //! updates the checksum field of the specified structure, call this for a structure after you modify its fields
  template<class T> void updateChecksum(T& cmd) { cmd.checksum=~nchecksum(cmd,sizeof(cmd)-1); }

  //! returns true if markers and checksum are valid
  template<class T> bool validate(const T& msg) {
    const unsigned char MARKER=(unsigned char)-1U;
    if(msg.markerA!=MARKER || msg.markerB!=MARKER) return false;
    if(msg.resplen!=sizeof(msg)-4) return false;
    typeof(msg.checksum) chk = ~nchecksum(msg,sizeof(msg)-1);
    return chk == msg.checksum;
  }
  
  struct GenericCmdHeader {
    GenericCmdHeader(unsigned char bytelen, unsigned char instruction)
    : markerA(MARKER_VALUE), markerB(MARKER_VALUE), servoid(BROADCAST_ID), cmdlen(bytelen),  cmdid(instruction) {}
    operator const char*() const { return reinterpret_cast<const char*>(&markerA); }
    operator const unsigned char*() const { return &markerA; }
    unsigned char markerA;
    unsigned char markerB;
    unsigned char servoid;
    unsigned char cmdlen;
    unsigned char cmdid;
  };
  inline unsigned char nchecksum(const struct GenericCmdHeader& p, size_t len) { return nchecksum(p,len,2); }
  
  
  //! Allows you to do a "synchronized write", where all recipients commit the value(s) at the same time, and do not send any response packets
  /*! To do a synchronized write, first send a SyncWriteHeader indicating the type of write command
   *  being sent (T for example below) and the number of entries.
   *  Then send the corresponing entries themselves, followed by a checksum:
   * - unsigned char checksum = 0;
   * - write( os, SyncWriteHeader<T>(n), checksum );
   * - for(int i=0; i<n; ++i) { write( os, t[i], checksum ); }
   * - os.put(~checksum); // note bitwise-not!
   */
  template<class T>
  struct SyncWriteHeader : public GenericCmdHeader {
    SyncWriteHeader(unsigned char len)
    : GenericCmdHeader(sizeof(T)*len+4,0x83), addr(T::ADDRESS), writelen(sizeof(T)-1) {}
    unsigned char addr;
    unsigned char writelen;
  };
  struct SyncWriteEntry {
    SyncWriteEntry() : servoid() {}
    SyncWriteEntry(unsigned char sid) : servoid(sid) {}
    operator const char*() const { return reinterpret_cast<const char*>(&servoid); }
    operator const unsigned char*() const { return &servoid; }
    unsigned char servoid;
  };
  //! An element that follows a SyncWriteHeader, controls position and speed
  struct SyncWritePosSpeedEntry : public SyncWriteEntry {
    SyncWritePosSpeedEntry() : SyncWriteEntry(), posl(), posh(), speedl(), speedh() {}
    SyncWritePosSpeedEntry(unsigned char sid, unsigned short pos, unsigned short speed)
    : SyncWriteEntry(sid), posl(pos), posh(pos>>8), speedl(speed), speedh(speed>>8) {}
    static const unsigned char ADDRESS=0x1E;
    unsigned char posl;
    unsigned char posh;
    unsigned char speedl;
    unsigned char speedh;
  };
  //! An element that follows a SyncWriteHeader, enables or disables continuous rotation mode
  struct SyncWriteContinuousRotationEntry : public SyncWriteEntry {
    SyncWriteContinuousRotationEntry() : SyncWriteEntry(), ccwlimitl(), ccwlimith() {}
    SyncWriteContinuousRotationEntry(unsigned char sid, bool enable) : SyncWriteEntry(sid), ccwlimitl(enable?0:0xFF), ccwlimith(enable?0:0x3) {}
    static const unsigned char ADDRESS=0x8;
    unsigned char ccwlimitl;
    unsigned char ccwlimith;
  };
  //! An element that follows a SyncWriteHeader, toggles LED value
  struct SyncWriteLEDEntry : public SyncWriteEntry {
    SyncWriteLEDEntry() : SyncWriteEntry(), led() {}
    SyncWriteLEDEntry(unsigned char sid, bool enable) : SyncWriteEntry(sid), led(enable?1:0) {}
    static const unsigned char ADDRESS=0x19;
    unsigned char led;
  };
  struct SyncWriteComplianceEntry : public SyncWriteEntry {
    SyncWriteComplianceEntry() : SyncWriteEntry(), cwmargin(), ccwmargin(), cwslope(), ccwslope() {}
    SyncWriteComplianceEntry(unsigned char sid, unsigned char margin, unsigned char slope) : SyncWriteEntry(sid), cwmargin(margin), ccwmargin(margin), cwslope(slope), ccwslope(slope) {}
    static const unsigned char ADDRESS=0x1A;
    unsigned char cwmargin;
    unsigned char ccwmargin;
    unsigned char cwslope;
    unsigned char ccwslope;
  };
  struct SyncWritePunchEntry : public SyncWriteEntry {
    SyncWritePunchEntry() : SyncWriteEntry(), punchl(), punchh() {}
    SyncWritePunchEntry(unsigned char sid, unsigned short punch) : SyncWriteEntry(sid), punchl(punch), punchh(punch>>8) {}
    static const unsigned char ADDRESS=0x30;
    unsigned char punchl;
    unsigned char punchh;
  };
  struct SyncWriteTorqueEntry : public SyncWriteEntry {
    SyncWriteTorqueEntry() : SyncWriteEntry(), maxTorqueL(), maxTorqueH() {}
    SyncWriteTorqueEntry(unsigned char sid, unsigned short max) : SyncWriteEntry(sid), maxTorqueL(max), maxTorqueH(max>>8) {}
    static const unsigned char ADDRESS=0x22;
    unsigned char maxTorqueL;
    unsigned char maxTorqueH;
  };
  //! clears the sound data max hold field of an AX-S1
  struct SyncWriteSoundHoldEntry : public SyncWriteEntry {
    SyncWriteSoundHoldEntry() : SyncWriteEntry(), sndMaxHold(0) {}
    SyncWriteSoundHoldEntry(unsigned char sid) : SyncWriteEntry(sid), sndMaxHold(0) {}
    static const unsigned char ADDRESS=0x24;
    unsigned char sndMaxHold; //!< the maximum microphone value from microphone (requires reset)
  };
  //! clears the sound detected count field of an AX-S1
  /* This can be sent after the count becomes non-zero to clear it so you can detect another count of the same magnitude.
   *  In other words, the AX-S1 count stays at zero until a time after the last increment, when the total count is posted to the register.
   *  You don't receive updates for individual increments to the counter — you receive only the total count at the end.
   *  So once you have read the total count, you should reset it. */
  struct SyncWriteSoundCountEntry : public SyncWriteEntry {
    SyncWriteSoundCountEntry() : SyncWriteEntry(), sndCount(0) {}
    SyncWriteSoundCountEntry(unsigned char sid) : SyncWriteEntry(sid), sndCount(0) {}
    static const unsigned char ADDRESS=0x25;
    unsigned char sndCount; //!< number of times the microphone reading has exceeded a threshold
  };
  //! clears the sound data max hold and sound detected count fields of an AX-S1 at the same time, see ClearSoundHold and ClearSoundCount
  struct SyncWriteSoundHoldAndCountEntry : public SyncWriteEntry {
    SyncWriteSoundHoldAndCountEntry() : SyncWriteEntry(), sndMaxHold(0), sndCount(0) {}
    SyncWriteSoundHoldAndCountEntry(unsigned char sid) : SyncWriteEntry(sid), sndMaxHold(0), sndCount(0) {}
    static const unsigned char ADDRESS=0x24;
    unsigned char sndMaxHold; //!< the maximum microphone value from microphone (requires reset)
    unsigned char sndCount; //!< number of times the microphone reading has exceeded a threshold
  };
  
  
  struct WriteHeader : public GenericCmdHeader {
    WriteHeader(unsigned char address, unsigned char len)
    : GenericCmdHeader(len+3,0x3), addr(address) {}
    unsigned char addr;
  };
  //! Broadcasts a 'torque enable' (or disable) command to all servos using a write command to the appropriate address
  struct BroadcastTorqueCmd : public WriteHeader {
    //! constructor, pass true to enable torque, false to cut power
    BroadcastTorqueCmd(bool enable)
    : WriteHeader(0x18,1), torqueEnable(enable?1:0), checksum() { updateChecksum(*this); }
    
    unsigned char torqueEnable; //!< non-zero to enable torque of the servo
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! Broadcasts a command to set controller parameters to 0, also disabling torque (see also BroadcastNoPunchCmd)
  struct BroadcastFullComplianceCmd : public WriteHeader {
    BroadcastFullComplianceCmd()
    : WriteHeader(0x1A,4), cwmargin(0), ccwmargin(0), cwslope(0), ccwslope(0), checksum() { updateChecksum(*this); }
    unsigned char cwmargin;
    unsigned char ccwmargin;
    unsigned char cwslope;
    unsigned char ccwslope;
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! Sets 'punch' parameter to 0, eliminating torque jump (see also BroadcastFullComplianceCmd)
  struct BroadcastNoPunchCmd : public WriteHeader {
    BroadcastNoPunchCmd()
    : WriteHeader(0x30,2), punchl(0), punchh(0), checksum() { updateChecksum(*this); }
    unsigned char punchl;
    unsigned char punchh;
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! Sets 'speed' parameter to 0, ensuring no motion will occur from leftover 'free spin' commands
  struct BroadcastZeroSpeedCmd : public WriteHeader {
    BroadcastZeroSpeedCmd()
    : WriteHeader(0x20,2), speedl(0), speedh(0), checksum() { updateChecksum(*this); }
    unsigned char speedl;
    unsigned char speedh;
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! Sets 'baud rate' parameter to the specified value, where resulting bits per second will be 2M / (baud+1)
  struct BroadcastBaudCmd : public WriteHeader {
    BroadcastBaudCmd(unsigned char divisor) : WriteHeader(0x04,1), baudDivisor(divisor), checksum() { updateChecksum(*this); }
    unsigned char baudDivisor;
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! Sets 'return delay time' parameter to the specified value, where actual delay time is 2µs * value
  struct SetReturnDelayTimeCmd : public WriteHeader {
    SetReturnDelayTimeCmd() : WriteHeader(0x05,1), delayTime(0), checksum() { updateChecksum(*this); }
    SetReturnDelayTimeCmd(unsigned char delay) : WriteHeader(0x05,1), delayTime(delay), checksum() { updateChecksum(*this); }
    SetReturnDelayTimeCmd(unsigned char sid, unsigned char delay) : WriteHeader(0x05,1), delayTime(delay), checksum() { servoid=sid; updateChecksum(*this); }
    unsigned char delayTime; //!< amount of time to delay before responding, in units of 2µs
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };  
  //! Sets 'status response level' parameter to the specified value, see StatusResponseLevel
  struct SetStatusResponseLevelCmd : public WriteHeader {
    SetStatusResponseLevelCmd() : WriteHeader(0x10,1), responseLevel(0), checksum() { updateChecksum(*this); }
    SetStatusResponseLevelCmd(StatusResponseLevel level) : WriteHeader(0x05,1), responseLevel(level), checksum() { updateChecksum(*this); }
    SetStatusResponseLevelCmd(unsigned char sid, StatusResponseLevel level) : WriteHeader(0x05,1), responseLevel(level), checksum() { servoid=sid; updateChecksum(*this); }
    unsigned char responseLevel; //!< see StatusResponseLevel
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };  
  //! Sends a command to change a servo's ID value (use carefully!)
  struct SetServoIDCmd : public WriteHeader {
    SetServoIDCmd(unsigned char tgtsid, unsigned char newsid)
    : WriteHeader(0x03, 1), newservoid(newsid), checksum() { servoid=tgtsid; updateChecksum(*this); }
    unsigned char newservoid;
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! Sets the position and speed for a single servo
  struct SetPosSpeedCmd : public WriteHeader {
    SetPosSpeedCmd() : WriteHeader(0x1E,4), posl(), posh(), speedl(), speedh(), checksum() { updateChecksum(*this); }
    SetPosSpeedCmd(unsigned char sid, unsigned short pos, unsigned short speed)
    : WriteHeader(0x1E,4), posl(pos), posh(pos>>8), speedl(speed), speedh(speed>>8), checksum() { servoid=sid; updateChecksum(*this); }
    unsigned char posl;
    unsigned char posh;
    unsigned char speedl;
    unsigned char speedh;
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! clears the sound data max hold field of an AX-S1
  struct ClearSoundHoldCmd : public WriteHeader {
    ClearSoundHoldCmd() : WriteHeader(0x24,1), sndMaxHold(0), checksum() { updateChecksum(*this); }
    ClearSoundHoldCmd(unsigned char sid) : WriteHeader(0x24,1), sndMaxHold(0), checksum() { servoid=sid; updateChecksum(*this); }
    unsigned char sndMaxHold; //!< the maximum microphone value from microphone (requires reset)
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! clears the sound detected count field of an AX-S1
  /* This can be sent after the count becomes non-zero to clear it so you can detect another count of the same magnitude.
   *  In other words, the AX-S1 count stays at zero until a time after the last increment, when the total count is posted to the register.
   *  You don't receive updates for individual increments to the counter — you receive only the total count at the end.
   *  So once you have read the total count, you should reset it. */
  struct ClearSoundCountCmd : public WriteHeader {
    ClearSoundCountCmd() : WriteHeader(0x25,1), sndCount(0), checksum() { updateChecksum(*this); }
    ClearSoundCountCmd(unsigned char sid) : WriteHeader(0x25,1), sndCount(0), checksum() { servoid=sid; updateChecksum(*this); }
    unsigned char sndCount; //!< number of times the microphone reading has exceeded a threshold
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! clears the sound data max hold and sound detected count fields of an AX-S1 at the same time, see ClearSoundHold and ClearSoundCount
  struct ClearSoundHoldAndCountCmd : public WriteHeader {
    ClearSoundHoldAndCountCmd() : WriteHeader(0x24,2), sndMaxHold(0), sndCount(0), checksum() { updateChecksum(*this); }
    ClearSoundHoldAndCountCmd(unsigned char sid) : WriteHeader(0x24,2), sndMaxHold(0), sndCount(0), checksum() { servoid=sid; updateChecksum(*this); }
    unsigned char sndMaxHold; //!< the maximum microphone value from microphone (requires reset)
    unsigned char sndCount; //!< number of times the microphone reading has exceeded a threshold
    char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  
  
  
  //! Provides bitmasks for checking various error conditions in GenericResponseHeader::error
  enum ResponseError_t {
    VOLTAGE_ERROR=1, ANGLE_ERROR=2, HEAT_ERROR=4, RANGE_ERROR=8, CHECKSUM_ERROR=16, LOAD_ERROR=32, INSTRUCTION_ERROR=64
  };
  extern const char* ResponseErrorNames[9];
  
  //! contains fields global to all response packets
  struct GenericResponseHeader {
    GenericResponseHeader() : markerA(0), markerB(0), servoid(0), resplen(0), error(0) {}
    operator char*() { return reinterpret_cast<char*>(&markerA); } //!< easy serialization
    operator const char*() const { return reinterpret_cast<const char*>(&markerA); } //!< easy serialization
    operator const unsigned char*() const { return &markerA; } //!< easy serialization
    unsigned char markerA;  //!< should always be 0xFF
    unsigned char markerB;  //!< should always be 0xFF
    unsigned char servoid;  //!< the ID of the servo who made the response
    unsigned char resplen;  //!< number of data bytes which follow, including error field and final checksum
    unsigned char error;    //!< error bitmask, see ResponseError_t
  };
  inline unsigned char nchecksum(const struct GenericResponseHeader& p, size_t len) { return nchecksum(p,len,2); }
  
  const unsigned char RESPONSE_HEADER_LEN = sizeof(GenericResponseHeader)+1;
  
  //! Expected response from a Write command (when sent to non-broadcast address)
  struct WriteResponse : public GenericResponseHeader {
    unsigned char checksum;
  };
  //! Expected response from a ReadServoSensorsCmd, common across AX, RX, and EX series at least
  struct ServoSensorsResponse : public GenericResponseHeader {
    //! constructor
    ServoSensorsResponse() : GenericResponseHeader(), posl(), posh(), speedl(), speedh(), loadl(), loadh(), voltage(), temp(), checksum() {}
    
    //! returns current position in 'tics', 10 bit resolution
    unsigned short getPosition() const { return (static_cast<unsigned short>(posh)<<8) + posl; }
    //! returns current speed as 'tics' per second, 11 bit signed resolution
    short getSpeed() const { short x = (static_cast<short>(speedh&0x3)<<8) | speedl; return (speedh&4) ? -x : x; }
    //! returns an indication of how hard the servo is working, 11 bit signed resolution; note we flip the sign from what the hardware provides
    short getLoad() const { short x = (static_cast<short>(loadh&0x3)<<8) | loadl; return (loadh&4) ? x : -x; }
    
    unsigned char posl;       //!< low byte of position
    unsigned char posh;       //!< high byte of position
    unsigned char speedl;       //!< low byte of speed
    unsigned char speedh;       //!< high byte of speed
    unsigned char loadl;      //!< low byte of load
    unsigned char loadh;      //!< high byte of load
    unsigned char voltage;      //!< voltage times 10
    unsigned char temp;       //!< temperature (Celsius)
    unsigned char checksum;       //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! Expected response from a ReadAXS1SensorsCmd
  struct AXS1SensorsResponse : public GenericResponseHeader {
    //! constructor
    AXS1SensorsResponse() : GenericResponseHeader(),
      leftIR(), centerIR(), rightIR(), leftLum(), centerLum(), rightLum(),
      obsFlag(), lumFlag(), _robotisReserved(), sndData(), sndMaxHold(), sndCount(),
      /*sndTimeLow(), sndTimeHigh(), buzzerIndex(), buzzerTime(), voltage(), temp(), */
      checksum()
    {}
    
    /*
    //! timestamp of last #detCount increment, 16MHz timing: advances by 16000 per ms
    unsigned short getDetectedTime() {
      return (static_cast<unsigned short>(sndTimeHigh)<<8) + sndTimeLow;
    }
     */

    unsigned char leftIR; //!< reflectance from the left
    unsigned char centerIR; //!< reflectance from the center
    unsigned char rightIR; //!< reflectance from the right
    unsigned char leftLum; //!< external illumination from the left
    unsigned char centerLum; //!< external illumination from the center
    unsigned char rightLum; //!< external illumination from the right
    unsigned char obsFlag; //!< bitset indicating whether #leftIR, #centerIR, or #rightIR have exceeded a threshold (unused, requires reset)
    unsigned char lumFlag; //!< bitset indicating whether #leftLum, #centerLum, or #rightLum have exceeded a threshold (unused, requires reset)
    unsigned char _robotisReserved; //!< unused
    unsigned char sndData; //!< current pressure reading from microphone (unused, not sampled frequently enough to be useful)
    unsigned char sndMaxHold; //!< the maximum microphone value from microphone (requires reset)
    unsigned char sndCount; //!< number of times the microphone reading has exceeded a threshold
    /*
    unsigned char sndTimeLow; //!< timestamp of last #detCount increment, 16MHz timing: advances by 16000 per ms (low order byte)
    unsigned char sndTimeHigh; //!< timestamp of last #detCount increment, 16MHz timing: advances by 16000 per ms (high order byte)
    unsigned char buzzerIndex; //!< the note to play, 0-51 inclusive (command value); if #buzzerTime is set to 255, then 0-26 inclusive to select a score (command value)
    unsigned char buzzerTime; //!< time to play the note for in tenths of a second, 0-50; 254 plays continuously, 255 plays scores via #buzzerIndex (command value)
    unsigned char voltage; //!< voltage times 10
    unsigned char temp; //!< temperature (Celsius)
     */
    unsigned char checksum; //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! Expected response from a ReadTorqueCmd
  struct TorqueResponse : public GenericResponseHeader {
    unsigned char torqueEnable;  //!< if non-zero, torque is enabled on the servo (false indicates an error may have occurred)
    unsigned char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! Expected response from a ReadModelCmd
  struct ServoInfoResponse : public GenericResponseHeader {
    ServoInfoResponse() : GenericResponseHeader(), modell(0), modelh(0), version(0), checksum() {}
    unsigned short getModelNumber() const { return (static_cast<unsigned short>(modelh)<<8) | modell; }
    const char* getModelString() const {
      typedef typeof(dynamixelModels) modelmap_t;
      modelmap_t::const_iterator it = dynamixelModels.find((ModelID_t)getModelNumber());
      if(it==dynamixelModels.end()) {
        return (getModelNumber()==0 && version==0) ? "INVALID RESPONSE" : MODEL_UNKNOWN_NAME;
      } else {
        return it->second.c_str();
      }
    }
    unsigned char modell;  //!< indicates low byte of model number
    unsigned char modelh;  //!< indicates high byte of model number
    unsigned char version;  //!< firmware version
    unsigned char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  
  
  
  //! Contains fields which are global to all read commands, which can read a block of parameters from the unit
  struct ReadCmd : public GenericCmdHeader {
    //! constructor, pass the unit ID, the starting address, and the number of bytes to read
    ReadCmd(unsigned char servoID, unsigned char address, unsigned char len)
      : GenericCmdHeader(4,0x2), addr(address), readlen(len), checksum() { servoid=servoID; updateChecksum(*this); }
    unsigned char addr;  //!< address to start reading from on the unit
    unsigned char readlen;  //!< number of bytes to read
    unsigned char checksum;  //!< checksum value (bitwise negated sum of all non-marker fields), see nchecksum()
  };
  //! Requests a block of servo sensor values be sent, servo should respond with a ServoSensorsResponse
  struct ReadServoSensorsCmd : public ReadCmd {
    //! constructor, pass the ID of the servo you want to query
    ReadServoSensorsCmd(unsigned char servoID) : ReadCmd(servoID,0x24,sizeof(ServoSensorsResponse)-RESPONSE_HEADER_LEN) {}
  };
  //! Requests a block of AX-S1 sensor values be sent, module should respond with a AXS1SensorsResponse
  struct ReadAXS1SensorsCmd : public ReadCmd {
    //! constructor, pass the ID of the servo you want to query
    ReadAXS1SensorsCmd(unsigned char servoID) : ReadCmd(servoID,0x1A,sizeof(AXS1SensorsResponse)-RESPONSE_HEADER_LEN) {}
  };
  //! Requests the 'torque enable' status be sent, servo should respond with a TorqueResponse
  struct ReadTorqueCmd : public ReadCmd {
    //! constructor, pass the ID of the servo you want to query
    ReadTorqueCmd(unsigned char servoID) : ReadCmd(servoID,0x18,sizeof(TorqueResponse)-RESPONSE_HEADER_LEN) {}
  };
  //! Requests the 'model number' be sent, servo should respond with a ServoInfoResponse
  struct ReadModelCmd : public ReadCmd {
    //! constructor, pass the ID of the servo you want to query
    ReadModelCmd(unsigned char servoID) : ReadCmd(servoID,0x00,sizeof(ServoInfoResponse)-RESPONSE_HEADER_LEN) {}
  };
  
  
  
  void reportErrors(unsigned int servoID, unsigned int offset, unsigned char err);
  
  //! reads a response from an input stream, attempts to handle line noise before response
  /*! returns false if an invalid response type is received */
  template<class R> bool readResponse(std::istream& is, R& response, unsigned int offset) {
    //std::cout << "reading markers..." << std::endl;
    is.read((char*)&response.markerA,sizeof(response.markerA)*2);
    if(!is || is.gcount()!=sizeof(response.markerA)*2) {
      Thread::testCurrentCancel();
      std::cerr << "Dynamixel protocol bad read! 1" << std::endl;
      is.sync();
      is.clear();
      return false;
    }
    size_t noiseCnt=0;
    //std::cout << "got markers " << (int)response.markerA << ' ' << (int)response.markerB << std::endl;
    while(response.markerA!=DynamixelProtocol::MARKER_VALUE || response.markerB!=DynamixelProtocol::MARKER_VALUE) {
      //std::cout << "re-reading markers " << (int)response.markerA << ' ' << (int)response.markerB << std::endl;
      ++noiseCnt;
      response.markerA=response.markerB;
      try {
        is.read((char*)&response.markerB,sizeof(response.markerB));
        if(!is || is.gcount()!=sizeof(response.markerB)) {
          Thread::testCurrentCancel();
          std::cerr << "Dynamixel protocol bad read! 2" << std::endl;
          is.sync();
          is.clear();
        }
      } catch(...) {
        std::cerr << "Dynamixel protocol couldn't find packet start, skipped " << noiseCnt << " bytes of line noise." << std::endl;
        throw;
      }
    }
    if(noiseCnt!=0)
      std::cerr << "Dynamixel protocol skipping " << noiseCnt << " bytes of line noise" << std::endl;
    const size_t HEADER_SIZE = sizeof(response.servoid)+sizeof(response.resplen)+sizeof(response.error);
    //std::cout << "reading header " << HEADER_SIZE << std::endl;
    is.read((char*)&response.servoid,HEADER_SIZE);
    if(!is || (size_t)is.gcount()!=HEADER_SIZE) {
      Thread::testCurrentCancel();
      std::cerr << "Dynamixel protocol bad read! 3" << std::endl;
      is.sync();
      is.clear();
      return false;
    }
    if(response.resplen<2) {
      std::cerr << "Dynamixel protocol got bad packet, too short! (" << (int)response.resplen << ")" << std::endl;
      return false;
    }
    //std::cout << "got header from " << (int)response.servoid << std::endl;
    if(response.resplen != sizeof(R)-sizeof(GenericResponseHeader)+1) {
      unsigned char tmpbuf[256];
      memcpy(tmpbuf,&response.servoid,HEADER_SIZE);
      is.read((char*)tmpbuf+HEADER_SIZE,response.resplen-sizeof(response.error));
      if(!is || (size_t)is.gcount()!=response.resplen-sizeof(response.error)) {
        Thread::testCurrentCancel();
        std::cerr << "Dynamixel protocol bad read! 4" << std::endl;
        is.sync();
        is.clear();
        return false;
      }
      unsigned char rchksum = tmpbuf[HEADER_SIZE+response.resplen-sizeof(response.error)-1];
      unsigned char lchksum = ~nchecksum(tmpbuf,HEADER_SIZE+response.resplen-sizeof(response.error)-1,0);
      if( lchksum == rchksum) {
        if(response.error==0)
          std::cerr << "Dynamixel protocol: invalid response (expected " << (sizeof(R)-sizeof(GenericResponseHeader)+1) << ", length=" << (int)response.resplen << ")" << std::endl;
        else
          reportErrors(response.servoid,offset,response.error);
      } else {
        std::cerr << "Dynamixel line noise: sensor checksum failed" << std::endl;
        is.sync();
      }
      return false;
    }
    
    //std::cout << "Header complete, reading payload size " << response.resplen-sizeof(response.error) << std::endl;
    is.read((char*)(&response.error+1),response.resplen-sizeof(response.error));
    if(!is || (size_t)is.gcount()!=response.resplen-sizeof(response.error)) {
      Thread::testCurrentCancel();
      std::cerr << "Dynamixel protocol bad read! 5" << std::endl;
      is.sync();
      is.clear();
      return false;
    } else if(!validate(response)) {
      /*std::cerr << "Sensor checksum failed, response was: " << std::flush; 
      debuget::hexout(response,sizeof(response));
      std::cerr << "checksum: " << std::flush;
      debuget::charhexout(~nchecksum(response,response.resplen+3)); std::cout.flush();
      std::cerr << std::endl;*/
      std::cerr << "Dynamixel line noise: sensor checksum failed" << std::endl;
      is.sync();
      return false;
    }
    
    if(response.error!=0)
      reportErrors(response.servoid,offset,response.error);
    return true;
  }
  
  //! Attempts to ping the specified servo by reading its model number, and if successful, current sensor values
  /*! The run() call returns with the model string if successful, or NULL if the ping timed out */
  class PingThread : public Thread {
  public:
    //! constructor, pass input and output streams, the servo id, and optional sensor response to be filled in
    PingThread(std::istream& is, std::ostream& os, unsigned char servoid, unsigned int outputOffset, ServoSensorsResponse* servoinfo=NULL, AXS1SensorsResponse* servoinfoS1=NULL)
      : Thread(), response(), icomm(is), ocomm(os), sid(servoid), output(outputOffset), info(servoinfo), infoS1(servoinfoS1), unknownModelName() { start(); }
    //! destructor, stop and join thread
    ~PingThread() { if(isStarted()) stop().join(); }
    
    static long getTimeout() { return timeout; } //!< get #timeout
    static void setTimeout(long t) { timeout = t; } //!< set #timeout
    
    ServoInfoResponse response;
    
  protected:
    virtual void * run();
    virtual void cancelled();
    static long timeout; //!< time to wait for a response before giving up (in milliseconds)
    std::istream& icomm;  //!< input stream
    std::ostream& ocomm;  //!< output stream
    unsigned char sid;  //!< servo id value
    unsigned int output; //!< output offset
    ServoSensorsResponse* info;  //!< response to be filled in if successful and the servo is servo following common Dynamixel servo register layout.
    AXS1SensorsResponse* infoS1;  //!< response to be filled in if successful and the servo is an AX-S1 model.
    std::string unknownModelName; //!< temporary storage to append the model number to 

  private:
    PingThread(const PingThread&); //!< dummy
    PingThread& operator=(const PingThread&); //!< dummy
  };
  
  // this is a bad idea because it lets you encode 'pure' headers, where the actual data is just junk values following the header
  //inline std::ostream& operator<<(std::ostream& os, const GenericCmdHeader& cmd) { return os.write(cmd,cmd.cmdlen+4); }
  
  //! writes a command into a stream, returning the stream for convenient ostream::flush call.
  template<class T> std::ostream& write(std::ostream& os, const T& cmd) { return os.write(cmd,sizeof(cmd)); }
  //! writes a command into a stream and incrementing a checksum, returning the stream for convenient ostream::flush call.  Remember to bitwise-not (~) the checksum before transmission!
  template<class T> std::ostream& write(std::ostream& os, const T& cmd, unsigned char& checksum) { checksum+=nchecksum(cmd,sizeof(cmd)); return os.write(cmd,sizeof(cmd)); }
};

/*! @file
 * @brief 
 * @author Ethan Tira-Thompson (ejt) (Creator)
 */

#endif