Add ability to retrieve the TC fault cause

Author: JHSawatzki

src/utility/THERMOCOUPLE/MAX31855.cpp

@@ -146,9 +146,11 @@ float MAX31855Class::readTCTemperature() {
     rawword = readSensor();
 
     // Check for reading error
-    if (rawword & 0x7) {
+    lastFault = rawword & _faultMask;
+    if (_lastFault) {
         return NAN;
     }
+
     // The cold junction temperature is stored in the last 14 word's bits
     // whereas the ttermocouple temperature (non linearized) is in the topmost 18 bits
     // sent by the Thermocouple-to-Digital Converter
@@ -221,6 +223,15 @@ void MAX31855Class::setColdOffset(float offset) {
     _coldOffset = offset;
 }
 
+void MAX31855Class::setFaultChecks(uint8_t faults) {
+    _faultMask = faults & TC_FAULT_ALL;
+}
+
+uint8_t MAX31855Class::getLastFault() {
+    uint8_t tempLastFault = _lastFault;
+    _lastFault = 0;
+    return tempLastFault;
+}
 
 void MAX31855Class::setTCType(uint8_t type) {
     _current_probe_type = type;

src/utility/THERMOCOUPLE/MAX31855.h

@@ -14,6 +14,12 @@
 #define PROBE_J PROBE_TC_J
 #define PROBE_T PROBE_TC_T
 
+#define TC_FAULT_NONE      (0x00) // Disable all fault checks
+#define TC_FAULT_OPEN      (0x01) // Enable open circuit fault check
+#define TC_FAULT_SHORT_GND (0x02) // Enable short to GND fault check
+#define TC_FAULT_SHORT_VCC (0x04) // Enable short to VCC fault check
+#define TC_FAULT_ALL       (0x07) // Enable all fault checks
+
 class MAX31855Class {
 public:
     MAX31855Class(PinName cs = MC_TC_CS_PIN, SPIClass& spi = SPI);
@@ -24,11 +30,17 @@ class MAX31855Class {
     float readTCTemperature();
     float readReferenceTemperature();
     void setColdOffset(float offset);
+
+    void setFaultChecks(uint8_t faults);
+    uint8_t getLastFault();
+
     void setTCType(uint8_t type);
 
 private:
     uint32_t readSensor();
     float _coldOffset;
+    uint8_t _faultMask = TC_FAULT_ALL;
+    uint8_t _lastFault = 0;
     uint8_t _current_probe_type;
     PinName _cs;
     SPIClass* _spi;