marlin-lulzbot-laser/ArduinoAddons/Arduino_1.x.x/libraries/L6470/L6470.cpp

////////////////////////////////////////////////////////////
//ORIGINAL CODE 12/12/2011- Mike Hord, SparkFun Electronics
//LIBRARY Created by Adam Meyer of bildr Aug 18th 2012
//Released as MIT license
////////////////////////////////////////////////////////////

#include <Arduino.h>
#include "L6470.h"
#include <SPI.h>

#define ENABLE_RESET_PIN	0
#define K_VALUE			100

L6470::L6470(int SSPin){
  _SSPin = SSPin;
  // Serial.begin(9600);
}

void L6470::init(int k_value){
  // This is the generic initialization function to set up the Arduino to
  // communicate with the dSPIN chip.
  
  // set up the input/output pins for the application.
  pinMode(SLAVE_SELECT_PIN, OUTPUT); // The SPI peripheral REQUIRES the hardware SS pin-
  // pin 10- to be an output. This is in here just
  // in case some future user makes something other
  // than pin 10 the SS pin.
  
  pinMode(_SSPin, OUTPUT);
  digitalWrite(_SSPin, HIGH);
  pinMode(MOSI, OUTPUT);
  pinMode(MISO, INPUT);
  pinMode(SCK, OUTPUT);
  pinMode(BUSYN, INPUT);
#if (ENABLE_RESET_PIN == 1)
  pinMode(RESET, OUTPUT);
  // reset the dSPIN chip. This could also be accomplished by
  // calling the "L6470::ResetDev()" function after SPI is initialized.
  digitalWrite(RESET, HIGH);
  delay(10);
  digitalWrite(RESET, LOW);
  delay(10);
  digitalWrite(RESET, HIGH);
  delay(10);
#endif
  
  
  // initialize SPI for the dSPIN chip's needs:
  // most significant bit first,
  // SPI clock not to exceed 5MHz,
  // SPI_MODE3 (clock idle high, latch data on rising edge of clock)
  SPI.begin();
  SPI.setBitOrder(MSBFIRST);
  SPI.setClockDivider(SPI_CLOCK_DIV16); // or 2, 8, 16, 32, 64
  SPI.setDataMode(SPI_MODE3);
  
  // First things first: let's check communications. The CONFIG register should
  // power up to 0x2E88, so we can use that to check the communications.
  if (GetParam(CONFIG) == 0x2E88){
    //Serial.println('good to go');
  }
  else{
    //Serial.println('Comm issue');
  }

#if  (ENABLE_RESET_PIN == 0) 
  resetDev();
#endif
  // First, let's set the step mode register:
  // - SYNC_EN controls whether the BUSY/SYNC pin reflects the step
  // frequency or the BUSY status of the chip. We want it to be the BUSY
  // status.
  // - STEP_SEL_x is the microstepping rate- we'll go full step.
  // - SYNC_SEL_x is the ratio of (micro)steps to toggles on the
  // BUSY/SYNC pin (when that pin is used for SYNC). Make it 1:1, despite
  // not using that pin.
  //SetParam(STEP_MODE, !SYNC_EN | STEP_SEL_1 | SYNC_SEL_1);
  
  
  SetParam(KVAL_RUN, k_value);
  SetParam(KVAL_ACC, k_value);
  SetParam(KVAL_DEC, k_value);
  SetParam(KVAL_HOLD, k_value);
  
  // Set up the CONFIG register as follows:
  // PWM frequency divisor = 1
  // PWM frequency multiplier = 2 (62.5kHz PWM frequency)
  // Slew rate is 290V/us
  // Do NOT shut down bridges on overcurrent
  // Disable motor voltage compensation
  // Hard stop on switch low
  // 16MHz internal oscillator, nothing on output
  SetParam(CONFIG, CONFIG_PWM_DIV_1 | CONFIG_PWM_MUL_2 | CONFIG_SR_290V_us| CONFIG_OC_SD_DISABLE | CONFIG_VS_COMP_DISABLE | CONFIG_SW_HARD_STOP | CONFIG_INT_16MHZ);
  // Configure the RUN KVAL. This defines the duty cycle of the PWM of the bridges
  // during running. 0xFF means that they are essentially NOT PWMed during run; this
  // MAY result in more power being dissipated than you actually need for the task.
  // Setting this value too low may result in failure to turn.
  // There are ACC, DEC, and HOLD KVAL registers as well; you may need to play with
  // those values to get acceptable performance for a given application.
  //SetParam(KVAL_RUN, 0xFF);
  // Calling GetStatus() clears the UVLO bit in the status register, which is set by
  // default on power-up. The driver may not run without that bit cleared by this
  // read operation.
  getStatus();
  
  hardStop(); //engage motors
}

boolean L6470::isBusy(){
  int status = getStatus();
  return !((status >> 1) & 0b1);
}

void L6470::setMicroSteps(int microSteps){
  byte stepVal = 0;
  
  for(stepVal = 0; stepVal < 8; stepVal++){
    if(microSteps == 1) break;
    microSteps = microSteps >> 1;
  }

  SetParam(STEP_MODE, !SYNC_EN | stepVal | SYNC_SEL_1);
}

void L6470::setThresholdSpeed(float thresholdSpeed){
  // Configure the FS_SPD register- this is the speed at which the driver ceases
  // microstepping and goes to full stepping. FSCalc() converts a value in steps/s
  // to a value suitable for this register; to disable full-step switching, you
  // can pass 0x3FF to this register.
  
  if(thresholdSpeed == 0.0){
    SetParam(FS_SPD, 0x3FF);
  }
  else{
    SetParam(FS_SPD, FSCalc(thresholdSpeed));	
  }
}


void L6470::setCurrent(int current){}



void L6470::setMaxSpeed(int speed){
  // Configure the MAX_SPEED register- this is the maximum number of (micro)steps per
  // second allowed. You'll want to mess around with your desired application to see
  // how far you can push it before the motor starts to slip. The ACTUAL parameter
  // passed to this function is in steps/tick; MaxSpdCalc() will convert a number of
  // steps/s into an appropriate value for this function. Note that for any move or
  // goto type function where no speed is specified, this value will be used.
  SetParam(MAX_SPEED, MaxSpdCalc(speed));
}


void L6470::setMinSpeed(int speed){
  // Configure the MAX_SPEED register- this is the maximum number of (micro)steps per
  // second allowed. You'll want to mess around with your desired application to see
  // how far you can push it before the motor starts to slip. The ACTUAL parameter
  // passed to this function is in steps/tick; MaxSpdCalc() will convert a number of
  // steps/s into an appropriate value for this function. Note that for any move or
  // goto type function where no speed is specified, this value will be used.
  SetParam(MIN_SPEED, MinSpdCalc(speed));
}




void L6470::setAcc(float acceleration){
  // Configure the acceleration rate, in steps/tick/tick. There is also a DEC register;
  // both of them have a function (AccCalc() and DecCalc() respectively) that convert
  // from steps/s/s into the appropriate value for the register. Writing ACC to 0xfff
  // sets the acceleration and deceleration to 'infinite' (or as near as the driver can
  // manage). If ACC is set to 0xfff, DEC is ignored. To get infinite deceleration
  // without infinite acceleration, only hard stop will work.
  unsigned long accelerationBYTES = AccCalc(acceleration);
  SetParam(ACC, accelerationBYTES);
}


void L6470::setDec(float deceleration){
  unsigned long decelerationBYTES = DecCalc(deceleration);
  SetParam(DEC, decelerationBYTES);
}


long L6470::getPos(){
  unsigned long position = GetParam(ABS_POS);
  return convert(position);
}

float L6470::getSpeed(){
  /*
  SPEED
  The SPEED register contains the current motor speed, expressed in step/tick (format unsigned fixed point 0.28).
  In order to convert the SPEED value in step/s the following formula can be used:
  Equation 4
  where SPEED is the integer number stored into the register and tick is 250 ns.
  The available range is from 0 to 15625 step/s with a resolution of 0.015 step/s.
  Note: The range effectively available to the user is limited by the MAX_SPEED parameter.
  */
  
  return (float) GetParam(SPEED);
  //return (float) speed * pow(8, -22);
  //return FSCalc(speed); NEEDS FIX
}


void L6470::setOverCurrent(unsigned int ma_current){
  // Configure the overcurrent detection threshold.
  byte OCValue = floor(ma_current / 375);
  if(OCValue > 0x0F)OCValue = 0x0F;
  SetParam(OCD_TH, OCValue);
}

void L6470::setStallCurrent(float ma_current){
  byte STHValue = (byte)floor(ma_current / 31.25);
  if(STHValue > 0x80)STHValue = 0x80;
  if(STHValue < 0)STHValue = 0;
  SetParam(STALL_TH, STHValue);
}

void L6470::SetLowSpeedOpt(boolean enable){
  // Enable or disable the low-speed optimization option. If enabling,
  // the other 12 bits of the register will be automatically zero.
  // When disabling, the value will have to be explicitly written by
  // the user with a SetParam() call. See the datasheet for further
  // information about low-speed optimization.
  Xfer(SET_PARAM | MIN_SPEED);
  if (enable) Param(0x1000, 13);
  else Param(0, 13);
}


void L6470::run(byte dir, float spd){
  // RUN sets the motor spinning in a direction (defined by the constants
  // FWD and REV). Maximum speed and minimum speed are defined
  // by the MAX_SPEED and MIN_SPEED registers; exceeding the FS_SPD value
  // will switch the device into full-step mode.
  // The SpdCalc() function is provided to convert steps/s values into
  // appropriate integer values for this function.
  unsigned long speedVal = SpdCalc(spd);
  
  Xfer(RUN | dir);
  if (speedVal > 0xFFFFF) speedVal = 0xFFFFF;
  Xfer((byte)(speedVal >> 16));
  Xfer((byte)(speedVal >> 8));
  Xfer((byte)(speedVal));
}


void L6470::Step_Clock(byte dir){
  // STEP_CLOCK puts the device in external step clocking mode. When active,
  // pin 25, STCK, becomes the step clock for the device, and steps it in
  // the direction (set by the FWD and REV constants) imposed by the call
  // of this function. Motion commands (RUN, MOVE, etc) will cause the device
  // to exit step clocking mode.
  Xfer(STEP_CLOCK | dir);
}

void L6470::move(long n_step){
  // MOVE will send the motor n_step steps (size based on step mode) in the
  // direction imposed by dir (FWD or REV constants may be used). The motor
  // will accelerate according the acceleration and deceleration curves, and
  // will run at MAX_SPEED. Stepping mode will adhere to FS_SPD value, as well.
  
  byte dir;
  
  if(n_step >= 0){
    dir = FWD;
  }
  else{
    dir = REV;
  }

  long n_stepABS = abs(n_step);
  
  Xfer(MOVE | dir); //set direction
  if (n_stepABS > 0x3FFFFF) n_step = 0x3FFFFF;
  Xfer((byte)(n_stepABS >> 16));
  Xfer((byte)(n_stepABS >> 8));
  Xfer((byte)(n_stepABS));
}

void L6470::goTo(long pos){
  // GOTO operates much like MOVE, except it produces absolute motion instead
  // of relative motion. The motor will be moved to the indicated position
  // in the shortest possible fashion.
  
  Xfer(GOTO);
  if (pos > 0x3FFFFF) pos = 0x3FFFFF;
  Xfer((byte)(pos >> 16));
  Xfer((byte)(pos >> 8));
  Xfer((byte)(pos));
}


void L6470::goTo_DIR(byte dir, long pos){
  // Same as GOTO, but with user constrained rotational direction.
  
  Xfer(GOTO_DIR);
  if (pos > 0x3FFFFF) pos = 0x3FFFFF;
  Xfer((byte)(pos >> 16));
  Xfer((byte)(pos >> 8));
  Xfer((byte)(pos));
}

void L6470::goUntil(byte act, byte dir, unsigned long spd){
  // GoUntil will set the motor running with direction dir (REV or
  // FWD) until a falling edge is detected on the SW pin. Depending
  // on bit SW_MODE in CONFIG, either a hard stop or a soft stop is
  // performed at the falling edge, and depending on the value of
  // act (either RESET or COPY) the value in the ABS_POS register is
  // either RESET to 0 or COPY-ed into the MARK register.
  Xfer(GO_UNTIL | act | dir);
  if (spd > 0x3FFFFF) spd = 0x3FFFFF;
  Xfer((byte)(spd >> 16));
  Xfer((byte)(spd >> 8));
  Xfer((byte)(spd));
}

void L6470::releaseSW(byte act, byte dir){
  // Similar in nature to GoUntil, ReleaseSW produces motion at the
  // higher of two speeds: the value in MIN_SPEED or 5 steps/s.
  // The motor continues to run at this speed until a rising edge
  // is detected on the switch input, then a hard stop is performed
  // and the ABS_POS register is either COPY-ed into MARK or RESET to
  // 0, depending on whether RESET or COPY was passed to the function
  // for act.
  Xfer(RELEASE_SW | act | dir);
}

void L6470::goHome(){
  // GoHome is equivalent to GoTo(0), but requires less time to send.
  // Note that no direction is provided; motion occurs through shortest
  // path. If a direction is required, use GoTo_DIR().
  Xfer(GO_HOME);
}

void L6470::goMark(){
  // GoMark is equivalent to GoTo(MARK), but requires less time to send.
  // Note that no direction is provided; motion occurs through shortest
  // path. If a direction is required, use GoTo_DIR().
  Xfer(GO_MARK);
}


void L6470::setMark(long value){

  Xfer(MARK);
  if (value > 0x3FFFFF) value = 0x3FFFFF;
  if (value < -0x3FFFFF) value = -0x3FFFFF;
  
  
  Xfer((byte)(value >> 16));
  Xfer((byte)(value >> 8));
  Xfer((byte)(value));
}


void L6470::setMark(){
  long value = getPos();
  
  Xfer(MARK);
  if (value > 0x3FFFFF) value = 0x3FFFFF;
  if (value < -0x3FFFFF) value = -0x3FFFFF;
  
  
  Xfer((byte)(value >> 16));
  Xfer((byte)(value >> 8));
  Xfer((byte)(value));
}

void L6470::setAsHome(){
  // Sets the ABS_POS register to 0, effectively declaring the current
  // position to be "HOME".
  Xfer(RESET_POS);
}

void L6470::resetDev(){
  // Reset device to power up conditions. Equivalent to toggling the STBY
  // pin or cycling power.
  Xfer(RESET_DEVICE);
}

void L6470::softStop(){
  // Bring the motor to a halt using the deceleration curve.
  Xfer(SOFT_STOP);
}

void L6470::hardStop(){
  // Stop the motor right away. No deceleration.
  Xfer(HARD_STOP);
}

void L6470::softFree(){
  // Decelerate the motor and disengage
  Xfer(SOFT_HIZ);
}

void L6470::free(){
  // disengage the motor immediately with no deceleration.
  Xfer(HARD_HIZ);
}

int L6470::getStatus(){
  // Fetch and return the 16-bit value in the STATUS register. Resets
  // any warning flags and exits any error states. Using GetParam()
  // to read STATUS does not clear these values.
  int temp = 0;
  Xfer(GET_STATUS);
  temp = Xfer(0)<<8;
  temp |= Xfer(0);
  return temp;
}

unsigned long L6470::AccCalc(float stepsPerSecPerSec){
  // The value in the ACC register is [(steps/s/s)*(tick^2)]/(2^-40) where tick is
  // 250ns (datasheet value)- 0x08A on boot.
  // Multiply desired steps/s/s by .137438 to get an appropriate value for this register.
  // This is a 12-bit value, so we need to make sure the value is at or below 0xFFF.
  float temp = stepsPerSecPerSec * 0.137438;
  if( (unsigned long) long(temp) > 0x00000FFF) return 0x00000FFF;
  else return (unsigned long) long(temp);
}


unsigned long L6470::DecCalc(float stepsPerSecPerSec){
  // The calculation for DEC is the same as for ACC. Value is 0x08A on boot.
  // This is a 12-bit value, so we need to make sure the value is at or below 0xFFF.
  float temp = stepsPerSecPerSec * 0.137438;
  if( (unsigned long) long(temp) > 0x00000FFF) return 0x00000FFF;
  else return (unsigned long) long(temp);
}

unsigned long L6470::MaxSpdCalc(float stepsPerSec){
  // The value in the MAX_SPD register is [(steps/s)*(tick)]/(2^-18) where tick is
  // 250ns (datasheet value)- 0x041 on boot.
  // Multiply desired steps/s by .065536 to get an appropriate value for this register
  // This is a 10-bit value, so we need to make sure it remains at or below 0x3FF
  float temp = stepsPerSec * .065536;
  if( (unsigned long) long(temp) > 0x000003FF) return 0x000003FF;
  else return (unsigned long) long(temp);
}

unsigned long L6470::MinSpdCalc(float stepsPerSec){
  // The value in the MIN_SPD register is [(steps/s)*(tick)]/(2^-24) where tick is
  // 250ns (datasheet value)- 0x000 on boot.
  // Multiply desired steps/s by 4.1943 to get an appropriate value for this register
  // This is a 12-bit value, so we need to make sure the value is at or below 0xFFF.
  float temp = stepsPerSec * 4.1943;
  if( (unsigned long) long(temp) > 0x00000FFF) return 0x00000FFF;
  else return (unsigned long) long(temp);
}

unsigned long L6470::FSCalc(float stepsPerSec){
  // The value in the FS_SPD register is ([(steps/s)*(tick)]/(2^-18))-0.5 where tick is
  // 250ns (datasheet value)- 0x027 on boot.
  // Multiply desired steps/s by .065536 and subtract .5 to get an appropriate value for this register
  // This is a 10-bit value, so we need to make sure the value is at or below 0x3FF.
  float temp = (stepsPerSec * .065536)-.5;
  if( (unsigned long) long(temp) > 0x000003FF) return 0x000003FF;
  else return (unsigned long) long(temp);
}

unsigned long L6470::IntSpdCalc(float stepsPerSec){
  // The value in the INT_SPD register is [(steps/s)*(tick)]/(2^-24) where tick is
  // 250ns (datasheet value)- 0x408 on boot.
  // Multiply desired steps/s by 4.1943 to get an appropriate value for this register
  // This is a 14-bit value, so we need to make sure the value is at or below 0x3FFF.
  float temp = stepsPerSec * 4.1943;
  if( (unsigned long) long(temp) > 0x00003FFF) return 0x00003FFF;
  else return (unsigned long) long(temp);
}

unsigned long L6470::SpdCalc(float stepsPerSec){
  // When issuing RUN command, the 20-bit speed is [(steps/s)*(tick)]/(2^-28) where tick is
  // 250ns (datasheet value).
  // Multiply desired steps/s by 67.106 to get an appropriate value for this register
  // This is a 20-bit value, so we need to make sure the value is at or below 0xFFFFF.
  
  float temp = stepsPerSec * 67.106;
  if( (unsigned long) long(temp) > 0x000FFFFF) return 0x000FFFFF;
  else return (unsigned long)temp;
}

unsigned long L6470::Param(unsigned long value, byte bit_len){
  // Generalization of the subsections of the register read/write functionality.
  // We want the end user to just write the value without worrying about length,
  // so we pass a bit length parameter from the calling function.
  unsigned long ret_val=0; // We'll return this to generalize this function
  // for both read and write of registers.
  byte byte_len = bit_len/8; // How many BYTES do we have?
  if (bit_len%8 > 0) byte_len++; // Make sure not to lose any partial byte values.
  // Let's make sure our value has no spurious bits set, and if the value was too
  // high, max it out.
  unsigned long mask = 0xffffffff >> (32-bit_len);
  if (value > mask) value = mask;
  // The following three if statements handle the various possible byte length
  // transfers- it'll be no less than 1 but no more than 3 bytes of data.
  // L6470::Xfer() sends a byte out through SPI and returns a byte received
  // over SPI- when calling it, we typecast a shifted version of the masked
  // value, then we shift the received value back by the same amount and
  // store it until return time.
  if (byte_len == 3) {
    ret_val |= long(Xfer((byte)(value>>16))) << 16;
    //Serial.println(ret_val, HEX);
  }
  if (byte_len >= 2) {
    ret_val |= long(Xfer((byte)(value>>8))) << 8;
    //Serial.println(ret_val, HEX);
  }
  if (byte_len >= 1) {
    ret_val |= Xfer((byte)value);
    //Serial.println(ret_val, HEX);
  }
  // Return the received values. Mask off any unnecessary bits, just for
  // the sake of thoroughness- we don't EXPECT to see anything outside
  // the bit length range but better to be safe than sorry.
  return (ret_val & mask);
}

byte L6470::Xfer(byte data){
  // This simple function shifts a byte out over SPI and receives a byte over
  // SPI. Unusually for SPI devices, the dSPIN requires a toggling of the
  // CS (slaveSelect) pin after each byte sent. That makes this function
  // a bit more reasonable, because we can include more functionality in it.
  byte data_out;
  digitalWrite(_SSPin,LOW);
  // SPI.transfer() both shifts a byte out on the MOSI pin AND receives a
  // byte in on the MISO pin.
  data_out = SPI.transfer(data);
  digitalWrite(_SSPin,HIGH);
  return data_out;
}



void L6470::SetParam(byte param, unsigned long value){
  Xfer(SET_PARAM | param);
  ParamHandler(param, value);
}

unsigned long L6470::GetParam(byte param){
  // Realize the "get parameter" function, to read from the various registers in
  // the dSPIN chip.
  Xfer(GET_PARAM | param);
  return ParamHandler(param, 0);
}

long L6470::convert(unsigned long val){
  //convert 22bit 2s comp to signed long
  int MSB = val >> 21;
  
  val = val << 11;
  val = val >> 11;
  
  if(MSB == 1) val = val | 0b11111111111000000000000000000000;
  return val;
}

unsigned long L6470::ParamHandler(byte param, unsigned long value){
  // Much of the functionality between "get parameter" and "set parameter" is
  // very similar, so we deal with that by putting all of it in one function
  // here to save memory space and simplify the program.
  unsigned long ret_val = 0; // This is a temp for the value to return.
  // This switch structure handles the appropriate action for each register.
  // This is necessary since not all registers are of the same length, either
  // bit-wise or byte-wise, so we want to make sure we mask out any spurious
  // bits and do the right number of transfers. That is handled by the dSPIN_Param()
  // function, in most cases, but for 1-byte or smaller transfers, we call
  // Xfer() directly.
  switch (param)
  {
    // ABS_POS is the current absolute offset from home. It is a 22 bit number expressed
    // in two's complement. At power up, this value is 0. It cannot be written when
    // the motor is running, but at any other time, it can be updated to change the
    // interpreted position of the motor.
    case ABS_POS:
      ret_val = Param(value, 22);
      break;
    // EL_POS is the current electrical position in the step generation cycle. It can
    // be set when the motor is not in motion. Value is 0 on power up.
    case EL_POS:
      ret_val = Param(value, 9);
      break;
    // MARK is a second position other than 0 that the motor can be told to go to. As
    // with ABS_POS, it is 22-bit two's complement. Value is 0 on power up.
    case MARK:
      ret_val = Param(value, 22);
      break;
    // SPEED contains information about the current speed. It is read-only. It does
    // NOT provide direction information.
    case SPEED:
      ret_val = Param(0, 20);
      break;
    // ACC and DEC set the acceleration and deceleration rates. Set ACC to 0xFFF
    // to get infinite acceleration/decelaeration- there is no way to get infinite
    // deceleration w/o infinite acceleration (except the HARD STOP command).
    // Cannot be written while motor is running. Both default to 0x08A on power up.
    // AccCalc() and DecCalc() functions exist to convert steps/s/s values into
    // 12-bit values for these two registers.
    case ACC:
      ret_val = Param(value, 12);
      break;
    case DEC:
      ret_val = Param(value, 12);
      break;
    // MAX_SPEED is just what it says- any command which attempts to set the speed
    // of the motor above this value will simply cause the motor to turn at this
    // speed. Value is 0x041 on power up.
    // MaxSpdCalc() function exists to convert steps/s value into a 10-bit value
    // for this register.
    case MAX_SPEED:
      ret_val = Param(value, 10);
      break;
    // MIN_SPEED controls two things- the activation of the low-speed optimization
    // feature and the lowest speed the motor will be allowed to operate at. LSPD_OPT
    // is the 13th bit, and when it is set, the minimum allowed speed is automatically
    // set to zero. This value is 0 on startup.
    // MinSpdCalc() function exists to convert steps/s value into a 12-bit value for this
    // register. SetLowSpeedOpt() function exists to enable/disable the optimization feature.
    case MIN_SPEED:
      ret_val = Param(value, 12);
      break;
    // FS_SPD register contains a threshold value above which microstepping is disabled
    // and the dSPIN operates in full-step mode. Defaults to 0x027 on power up.
    // FSCalc() function exists to convert steps/s value into 10-bit integer for this
    // register.
    case FS_SPD:
      ret_val = Param(value, 10);
      break;
    // KVAL is the maximum voltage of the PWM outputs. These 8-bit values are ratiometric
    // representations: 255 for full output voltage, 128 for half, etc. Default is 0x29.
    // The implications of different KVAL settings is too complex to dig into here, but
    // it will usually work to max the value for RUN, ACC, and DEC. Maxing the value for
    // HOLD may result in excessive power dissipation when the motor is not running.
    case KVAL_HOLD:
      ret_val = Xfer((byte)value);
      break;
    case KVAL_RUN:
      ret_val = Xfer((byte)value);
      break;
    case KVAL_ACC:
      ret_val = Xfer((byte)value);
      break;
    case KVAL_DEC:
      ret_val = Xfer((byte)value);
      break;
    // INT_SPD, ST_SLP, FN_SLP_ACC and FN_SLP_DEC are all related to the back EMF
    // compensation functionality. Please see the datasheet for details of this
    // function- it is too complex to discuss here. Default values seem to work
    // well enough.
    case INT_SPD:
      ret_val = Param(value, 14);
      break;
    case ST_SLP:
      ret_val = Xfer((byte)value);
      break;
    case FN_SLP_ACC:
      ret_val = Xfer((byte)value);
      break;
    case FN_SLP_DEC:
      ret_val = Xfer((byte)value);
      break;
    // K_THERM is motor winding thermal drift compensation. Please see the datasheet
    // for full details on operation- the default value should be okay for most users.
    case K_THERM:
      ret_val = Xfer((byte)value & 0x0F);
      break;
    // ADC_OUT is a read-only register containing the result of the ADC measurements.
    // This is less useful than it sounds; see the datasheet for more information.
    case ADC_OUT:
      ret_val = Xfer(0);
      break;
    // Set the overcurrent threshold. Ranges from 375mA to 6A in steps of 375mA.
    // A set of defined constants is provided for the user's convenience. Default
    // value is 3.375A- 0x08. This is a 4-bit value.
    case OCD_TH:
      ret_val = Xfer((byte)value & 0x0F);
      break;
    // Stall current threshold. Defaults to 0x40, or 2.03A. Value is from 31.25mA to
    // 4A in 31.25mA steps. This is a 7-bit value.
    case STALL_TH:
      ret_val = Xfer((byte)value & 0x7F);
      break;
    // STEP_MODE controls the microstepping settings, as well as the generation of an
    // output signal from the dSPIN. Bits 2:0 control the number of microsteps per
    // step the part will generate. Bit 7 controls whether the BUSY/SYNC pin outputs
    // a BUSY signal or a step synchronization signal. Bits 6:4 control the frequency
    // of the output signal relative to the full-step frequency; see datasheet for
    // that relationship as it is too complex to reproduce here.
    // Most likely, only the microsteps per step value will be needed; there is a set
    // of constants provided for ease of use of these values.
    case STEP_MODE:
      ret_val = Xfer((byte)value);
      break;
    // ALARM_EN controls which alarms will cause the FLAG pin to fall. A set of constants
    // is provided to make this easy to interpret. By default, ALL alarms will trigger the
    // FLAG pin.
    case ALARM_EN:
      ret_val = Xfer((byte)value);
      break;
    // CONFIG contains some assorted configuration bits and fields. A fairly comprehensive
    // set of reasonably self-explanatory constants is provided, but users should refer
    // to the datasheet before modifying the contents of this register to be certain they
    // understand the implications of their modifications. Value on boot is 0x2E88; this
    // can be a useful way to verify proper start up and operation of the dSPIN chip.
    case CONFIG:
      ret_val = Param(value, 16);
      break;
      // STATUS contains read-only information about the current condition of the chip. A
      // comprehensive set of constants for masking and testing this register is provided, but
      // users should refer to the datasheet to ensure that they fully understand each one of
      // the bits in the register.
    case STATUS: // STATUS is a read-only register
      ret_val = Param(0, 16);
      break;
    default:
      ret_val = Xfer((byte)(value));
    break;
  }
  return ret_val;
}