DAC patches

As suggested by #4985

Marlin/dac_mcp4728.cpp

   mcp4728_values[channel] = value;
   return mcp4728_fastWrite();
 }
+
 /**
  * Write all input resistor values to EEPROM using SequencialWrite method.
  * This will update both input register and EEPROM value
 uint8_t mcp4728_eepromWrite() {
   Wire.beginTransmission(DAC_DEV_ADDRESS);
   Wire.write(SEQWRITE);
-  for (uint8_t channel = 0; channel < COUNT(channel); channel++) {
+  for (uint8_t channel = 0; channel < COUNT(mcp4728_values); channel++) {
     Wire.write(DAC_STEPPER_VREF << 7 | DAC_STEPPER_GAIN << 4 | highByte(mcp4728_values[channel]));
     Wire.write(lowByte(mcp4728_values[channel]));
   }
 }
 */
 
-/* Returns DAC values as a 0-100 percentage of drive strength */
+/**
+ * Returns DAC values as a 0-100 percentage of drive strength
+ */
 uint16_t mcp4728_getDrvPct(uint8_t channel) { return uint16_t(100.0 * mcp4728_values[channel] / (DAC_STEPPER_MAX) + 0.5); }
 
-/* Recieves all Drive strengths as 0-100 percent values, updates DAC Values array and calls fastwrite to update the DAC */
+/**
+ * Receives all Drive strengths as 0-100 percent values, updates
+ * DAC Values array and calls fastwrite to update the DAC.
+ */
 void mcp4728_setDrvPct(int16_t pct[XYZE]) {
   LOOP_XYZE(i) mcp4728_values[i] = 0.01 * pct[i] * (DAC_STEPPER_MAX);
   mcp4728_fastWrite();
  */
 uint8_t mcp4728_fastWrite() {
   Wire.beginTransmission(DAC_DEV_ADDRESS);
-  for (uint8_t channel = 0; channel < COUNT(channel); channel++) {
+  for (uint8_t channel = 0; channel < COUNT(mcp4728_values); channel++) {
     Wire.write(highByte(mcp4728_values[channel]));
     Wire.write(lowByte(mcp4728_values[channel]));
   }

Marlin/dac_mcp4728.h

  * Arduino library for MicroChip MCP4728 I2C D/A converter.
  */
 
-#ifndef mcp4728_h
-#define mcp4728_h
+#ifndef DAC_MCP4728_H
+#define DAC_MCP4728_H
 
 #include "MarlinConfig.h"
 
 void mcp4728_setDrvPct(int16_t pct[XYZE]);
 
 #endif
-#endif
-
+#endif // DAC_MCP4728_H

Marlin/stepper_dac.cpp

   }
 
   static float dac_perc(int8_t n) { return 100.0 * mcp4728_getValue(dac_order[n]) * (1.0 / (DAC_STEPPER_MAX)); }
-  static float dac_amps(int8_t n) { return mcp4728_getDrvPct(dac_order[n]) * (DAC_STEPPER_MAX) * (0.125 * (DAC_STEPPER_SENSE)); }
+  static float dac_amps(int8_t n) { return mcp4728_getDrvPct(dac_order[n]) * (DAC_STEPPER_MAX) * 0.125 * (1.0 / (DAC_STEPPER_SENSE)); }
   
   int16_t dac_current_get_percent(AxisEnum axis) { return mcp4728_getDrvPct(dac_order[axis]); }
   void dac_current_set_percents(int16_t pct[XYZE]) {