added some comments

sonoff/xsns_39_max31855.ino

@@ -17,8 +17,6 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-//#define USE_MAX31855
-
 #ifdef USE_MAX31855
 
 #define XSNS_39              39
@@ -26,24 +24,31 @@
 bool initialized = false;
 
 struct MAX31855_ResultStruct{
-    uint8_t ErrorCode;
+    uint8_t ErrorCode;                  // Error Codes: 0 = No Error / 1 = TC open circuit / 2 = TC short to GND / 4 = TC short to VCC
-    float ProbeTemperature;
+    float ProbeTemperature;             // Measured temperature of the 'hot' TC junction (probe temp)
-    float ReferenceTemperature;
+    float ReferenceTemperature;         // Measured temperature of the 'cold' TC junction (reference temp)
 } MAX31855_Result;
 
 void MAX31855_Init(void){
     if(initialized)
         return;
 
+    // Set GPIO modes for SW-SPI
     pinMode(pin[GPIO_MAX31855CS], OUTPUT);
     pinMode(pin[GPIO_MAX31855CLK], OUTPUT);
     pinMode(pin[GPIO_MAX31855DO], INPUT);
+
+    // Chip not selected / Clock low
     digitalWrite(pin[GPIO_MAX31855CS], HIGH);
     digitalWrite(pin[GPIO_MAX31855CLK], LOW);
 
     initialized = true;
 }
 
+/*
+*   MAX31855_GetResult(void)
+*   Acquires the raw data via SPI, checks for MAX31855 errors and fills result structure
+*/
 void MAX31855_GetResult(void){
     int32_t RawData = MAX31855_ShiftIn(32);
     uint8_t probeerror = RawData & 0x7;
@@ -51,51 +56,64 @@ void MAX31855_GetResult(void){
     MAX31855_Result.ErrorCode = probeerror;
     MAX31855_Result.ReferenceTemperature = MAX31855_GetReferenceTemperature(RawData);
     if(probeerror)
-        MAX31855_Result.ProbeTemperature = NAN;
+        MAX31855_Result.ProbeTemperature = NAN;     // Return NaN if MAX31855 reports an error
     else
         MAX31855_Result.ProbeTemperature = MAX31855_GetProbeTemperature(RawData);
 }
 
+
+/*
+*   MAX31855_GetProbeTemperature(int32_t RawData)
+*   Decodes and returns the temperature of TCs 'hot' junction from RawData
+*/
 float MAX31855_GetProbeTemperature(int32_t RawData){
     if(RawData & 0x80000000)
-        RawData = (RawData >> 18) | 0xFFFFC000;
+        RawData = (RawData >> 18) | 0xFFFFC000;     // Negative value - Drop lower 18 bits and extend to negative number
     else
-        RawData >>= 18;
+        RawData >>= 18;                             // Positiv value - Drop lower 18 bits
 
-    float result = (RawData * 0.25);
+    float result = (RawData * 0.25);                // MAX31855 LSB resolution is 0.25°C for probe temperature
 
-    return (Settings.flag.temperature_conversion) ? ConvertTemp(result) : result;
+    return (Settings.flag.temperature_conversion) ? ConvertTemp(result) : result;   // Check if we have to convert to Fahrenheit
 }
 
+/*
+*   MAX31855_GetReferenceTemperature(int32_t RawData)
+*   Decodes and returns the temperature of TCs 'cold' junction from RawData
+*/
 float MAX31855_GetReferenceTemperature(int32_t RawData){
     if(RawData & 0x8000)
-        RawData = (RawData >> 4) | 0xFFFFF000;
+        RawData = (RawData >> 4) | 0xFFFFF000;      // Negative value - Drop lower 4 bits and extend to negative number
     else
-        RawData = (RawData >> 4) & 0x00000FFF;
+        RawData = (RawData >> 4) & 0x00000FFF;      // Positiv value - Drop lower 4 bits and mask out remaining bits (probe temp, error bit, etc.)
 
-    float result = (RawData * 0.0625);
+    float result = (RawData * 0.0625);              // MAX31855 LSB resolution is 0.0625°C for reference temperature
 
-    return (Settings.flag.temperature_conversion) ? ConvertTemp(result) : result;
+    return (Settings.flag.temperature_conversion) ? ConvertTemp(result) : result;   // Check if we have to convert to Fahrenheit
 }
 
+/*
+*   MAX31855_ShiftIn(uint8_t Length)
+*   Communicates with MAX31855 via SW-SPI and returns the raw data read from the chip
+*/
 int32_t MAX31855_ShiftIn(uint8_t Length){
     int32_t dataIn = 0;
 
-    digitalWrite(pin[GPIO_MAX31855CS], LOW);
+    digitalWrite(pin[GPIO_MAX31855CS], LOW);            // CS = LOW -> Start SPI communication
-    delayMicroseconds(1);
+    delayMicroseconds(1);                               // CS fall to output enable = max. 100ns
     
     for(uint8_t i = 0; i < Length; i++)
     {
         digitalWrite(pin[GPIO_MAX31855CLK], LOW);
-        delayMicroseconds(1);
+        delayMicroseconds(1);                           // CLK pulse width low = min. 100ns / CLK fall to output valid = max. 40ns
         dataIn <<= 1;
         if(digitalRead(pin[GPIO_MAX31855DO]))
             dataIn |= 1;
         digitalWrite(pin[GPIO_MAX31855CLK], HIGH);
-        delayMicroseconds(1);
+        delayMicroseconds(1);                           // CLK pulse width high = min. 100ns
     }
 
-    digitalWrite(pin[GPIO_MAX31855CS], HIGH);
+    digitalWrite(pin[GPIO_MAX31855CS], HIGH);           // CS = HIGH -> End SPI communication
     digitalWrite(pin[GPIO_MAX31855CLK], LOW);
     return dataIn;    
 }
@@ -109,6 +127,16 @@ void MAX31855_Show(bool Json){
     if(Json){
         snprintf_P(mqtt_data, sizeof(mqtt_data), PSTR("%s,\"%s\":{\"" D_JSON_PROBETEMPERATURE "\":%s,\"" D_JSON_REFERENCETEMPERATURE "\":%s,\"" D_JSON_ERROR "\":%d}"), \
             mqtt_data, "MAX31855", probetemp, referencetemp, MAX31855_Result.ErrorCode);
+#ifdef USE_DOMOTICZ
+        if (0 == tele_period) {
+          DomoticzSensor(DZ_TEMP, probetemp);
+        }
+#endif  // USE_DOMOTICZ
+#ifdef USE_KNX
+        if (0 == tele_period) {
+          KnxSensor(KNX_TEMPERATURE, MAX31855_Result.ProbeTemperature);
+        }
+#endif  // USE_KNX
     } else {
 #ifdef USE_WEBSERVER
         snprintf_P(mqtt_data, sizeof(mqtt_data), HTTP_SNS_TEMP, mqtt_data, "MAX31855", probetemp, TempUnit());
@@ -116,20 +144,6 @@ void MAX31855_Show(bool Json){
     }
 }
 
-
-// void MAX31855_ShowDebug(void){
-//     char probetemp[33];
-//     char referencetemp[33];
-//     dtostrfd(MAX31855_Result.ProbeTemperature, Settings.flag2.temperature_resolution, probetemp);
-//     dtostrfd(MAX31855_Result.ReferenceTemperature, Settings.flag2.temperature_resolution, referencetemp);
-
-//     snprintf_P(mqtt_data, sizeof(mqtt_data), "%s %d %s %d %s %d %s %d %s %d %s %s %s %s %s %d", \
-//     "CS:", pin[GPIO_MAX31855CS], "CLK:", pin[GPIO_MAX31855CLK], "DO:", pin[GPIO_MAX31855DO], \
-//     "DO-State:", digitalRead(pin[GPIO_MAX31855DO]), \
-//     "RAW-Data:", MAX31855_ShiftIn(32), \
-//     "Probe-Temp:", probetemp, "Internal-Temp:", referencetemp, "Error:", MAX31855_Result.ErrorCode);
-// }
-
 /*********************************************************************************************\
  * Interface
 \*********************************************************************************************/
@@ -147,7 +161,6 @@ boolean Xsns39(byte function)
         MAX31855_GetResult();
         break;
       case FUNC_JSON_APPEND:
-        //MAX31855_ShowDebug();
         MAX31855_Show(true);
         break;
 #ifdef USE_WEBSERVER