Read Internal Temperature

cores/arduino/wiring.c

@@ -111,6 +111,10 @@ void init( void )
 
   analogReference( AR_DEFAULT ) ; // Analog Reference is AREF pin (3.3v)
 
+  SYSCTRL->VREF.reg |= SYSCTRL_VREF_TSEN; // Enable the temperature sensor  
+
+  while( ADC->STATUS.bit.SYNCBUSY == 1 ); // Wait for synchronization of registers between the clock domains
+
   // Initialize DAC
   // Setting clock
   while ( GCLK->STATUS.reg & GCLK_STATUS_SYNCBUSY );

cores/arduino/wiring_analog.c

@@ -312,6 +312,90 @@ void analogWrite(uint32_t pin, uint32_t value)
   }
 }
 
+// Reads temperature using internal ADC channel
+// Datasheet chapter 37.10.8 - Temperature Sensor Characteristics
+float readInternalTemperature()
+{
+  // Save ADC settings
+  uint16_t oldReadResolution = ADC->CTRLB.reg;
+  uint16_t oldSampling = ADC->SAMPCTRL.reg;
+  uint16_t oldReferenceGain = ADC->INPUTCTRL.bit.GAIN;
+  uint16_t oldReferenceSelect = ADC->REFCTRL.bit.REFSEL;
+
+  // Set to 12 bits resolution
+  ADC->CTRLB.reg = ADC_CTRLB_RESSEL_12BIT | ADC_CTRLB_PRESCALER_DIV256;
+  syncADC();
+
+  // Ensure we are sampling slowly
+  ADC->SAMPCTRL.reg = ADC_SAMPCTRL_SAMPLEN(0x3f);
+  syncADC();
+
+  // Set ADC reference to internal 1v
+  ADC->INPUTCTRL.bit.GAIN = ADC_INPUTCTRL_GAIN_1X_Val;
+  ADC->REFCTRL.bit.REFSEL = ADC_REFCTRL_REFSEL_INT1V_Val;
+  syncADC();
+
+  // Select MUXPOS as temperature channel, and MUXNEG  as internal ground
+  ADC->INPUTCTRL.bit.MUXPOS = ADC_INPUTCTRL_MUXPOS_TEMP_Val;
+  ADC->INPUTCTRL.bit.MUXNEG = ADC_INPUTCTRL_MUXNEG_GND_Val; 
+  syncADC();
+
+  // Enable ADC
+  ADC->CTRLA.bit.ENABLE = 1;
+  syncADC();
+
+  // Start ADC conversion
+  ADC->SWTRIG.bit.START = 1;
+
+  // Clear the Data Ready flag
+  ADC->INTFLAG.reg = ADC_INTFLAG_RESRDY;
+  syncADC();
+
+  // Start conversion again, since The first conversion after the reference is changed must not be used.
+  ADC->SWTRIG.bit.START = 1;
+
+  // Wait until ADC conversion is done
+  while (!(ADC->INTFLAG.bit.RESRDY));
+  syncADC();
+
+  // Get result
+  // This is signed so that the math later is done signed
+  int32_t adcReading = ADC->RESULT.reg;
+
+  // Clear result ready flag
+  ADC->INTFLAG.reg = ADC_INTFLAG_RESRDY; 
+  syncADC();
+
+  // Disable ADC
+  ADC->CTRLA.bit.ENABLE = 0; 
+  syncADC();
+
+  // Restore pervious ADC settings
+  ADC->CTRLB.reg = oldReadResolution;
+  syncADC();
+  ADC->SAMPCTRL.reg = oldSampling;
+  syncADC();
+  ADC->INPUTCTRL.bit.GAIN = oldReferenceGain;
+  ADC->REFCTRL.bit.REFSEL = oldReferenceSelect;
+  syncADC();  
+
+  // Factory room temperature readings
+  uint8_t roomInteger = (*(uint32_t*)FUSES_ROOM_TEMP_VAL_INT_ADDR & FUSES_ROOM_TEMP_VAL_INT_Msk) >> FUSES_ROOM_TEMP_VAL_INT_Pos;
+  uint8_t roomDecimal = (*(uint32_t*)FUSES_ROOM_TEMP_VAL_DEC_ADDR & FUSES_ROOM_TEMP_VAL_DEC_Msk) >> FUSES_ROOM_TEMP_VAL_DEC_Pos;
+  int32_t roomReading = ((*(uint32_t*)FUSES_ROOM_ADC_VAL_ADDR & FUSES_ROOM_ADC_VAL_Msk) >> FUSES_ROOM_ADC_VAL_Pos);
+  int32_t roomTemperature = 1000 * roomInteger + 100 * roomDecimal;
+
+  // Factory hot temperature readings
+  uint8_t hotInteger = (*(uint32_t*)FUSES_HOT_TEMP_VAL_INT_ADDR & FUSES_HOT_TEMP_VAL_INT_Msk) >> FUSES_HOT_TEMP_VAL_INT_Pos;
+  uint8_t hotDecimal = (*(uint32_t*)FUSES_HOT_TEMP_VAL_DEC_ADDR & FUSES_HOT_TEMP_VAL_DEC_Msk) >> FUSES_HOT_TEMP_VAL_DEC_Pos;
+  int32_t hotReading = ((*(uint32_t*)FUSES_HOT_ADC_VAL_ADDR & FUSES_HOT_ADC_VAL_Msk) >> FUSES_HOT_ADC_VAL_Pos);
+  int32_t hotTemperature = 1000 * hotInteger + 100 * hotDecimal;
+
+  // Linear interpolation of temperature using factory room temperature and hot temperature
+  int32_t temperature = roomTemperature + ((hotTemperature - roomTemperature) * (adcReading - roomReading)) / (hotReading - roomReading);
+  return temperature / 1000.0f;
+}
+
 #ifdef __cplusplus
 }
 #endif

cores/arduino/wiring_analog.h

@@ -79,6 +79,13 @@ extern void analogWriteResolution(int res);
 
 extern void analogOutputInit( void ) ;
 
+/*
+ * \brief Read the internal temperature using the temperature ADC channel.
+ *
+ * \return Temperature (°C)
+ */
+extern float readInternalTemperature();
+
 #ifdef __cplusplus
 }
 #endif