temp.c: use free-running readings in EMWA mode.

If we have EMWA mode turned on, then the user wants to average
several samples from the temp sensors over time. But now we read
temp sensors only 4 times per second making this averaging take
much longer.

Read the temperatures continuously -- as fast as supported by the
probe type -- if we are using weight averaging (TEMP_EMWA < 1.0).

temp.c

@@ -94,6 +94,13 @@ static struct {
   #define TEMP_EWMA 1.0
 #endif
 
+#define EWMA_SCALE  1024L
+#define EWMA_ALPHA  ((uint32_t)(TEMP_EWMA * EWMA_SCALE))
+
+// If EWMA is used, continuously update analog reading for more data points.
+#define TEMP_READ_CONTINUOUS (EWMA_ALPHA < EWMA_SCALE)
+#define TEMP_NOT_READY       0xffff
+
 /// Set up temp sensors.
 void temp_init() {
 	temp_sensor_t i;
@@ -251,7 +258,7 @@ static uint16_t temp_table_lookup(uint16_t temp, uint8_t sensor) {
 #endif /* TEMP_THERMISTOR || TEMP_MCP3008 */
 
 #ifdef TEMP_MAX6675
-static uint16_t temp_read_max6675(temp_sensor_t i) {
+static uint16_t temp_max6675_read(temp_sensor_t i) {
   // Note: value reading in this section was rewritten without
   //       testing when spi.c/.h was introduced. --Traumflug
   // Note: MAX6675 can give a reading every 0.22s
@@ -275,6 +282,18 @@ static uint16_t temp_read_max6675(temp_sensor_t i) {
 
   return temp;
 }
+
+static uint16_t temp_read_max6675(temp_sensor_t i) {
+  switch (temp_sensors_runtime[i].active++) {
+    case 1:
+      return temp_max6675_read(i);
+
+    case 22:  // read temperature at most every 220ms
+      temp_sensors_runtime[i].active = 0;
+      break;
+  }
+  return TEMP_NOT_READY;
+}
 #endif /* TEMP_MAX6675 */
 
 #ifdef TEMP_THERMISTOR
@@ -283,26 +302,27 @@ static uint16_t temp_read_thermistor(temp_sensor_t i) {
     case 1:  // Start ADC conversion.
       #ifdef NEEDS_START_ADC
         start_adc();
-        return 0;
+        return TEMP_NOT_READY;
       #endif
       // else fall through to conversion
 
     case 2:  // Convert temperature values.
       temp_sensors_runtime[i].active = 0;
       return temp_table_lookup(analog_read(i), i);
-
-    case 0:  // IDLE
-    default:
-      temp_sensors_runtime[i].active = 0;
-      return 0;
   }
+  return TEMP_NOT_READY;
 }
 #endif /* TEMP_THERMISTOR */
 
 #ifdef TEMP_MCP3008
 static uint16_t temp_read_mcp3008(temp_sensor_t i) {
-  temp_sensors_runtime[i].active = 0;
+  switch (temp_sensors_runtime[i].active++) {
-  return temp_table_lookup(mcp3008_read(temp_sensors[i].temp_pin), i);
+    case 1:
+      return temp_table_lookup(mcp3008_read(temp_sensors[i].temp_pin), i);
+    case 10:  // Idle for 100ms.
+      temp_sensors_runtime[i].active = 0;
+  }
+  return TEMP_NOT_READY;
 }
 #endif /* TEMP_MCP3008 */
 
@@ -312,7 +332,7 @@ static uint16_t temp_read_ad595(temp_sensor_t i) {
     case 1:  // Start ADC conversion.
       #ifdef NEEDS_START_ADC
         start_adc();
-        return 0;
+        return TEMP_NOT_READY;
       #endif
       // else fall through to conversion
 
@@ -321,34 +341,39 @@ static uint16_t temp_read_ad595(temp_sensor_t i) {
       // Convert >> 8 instead of >> 10 because internal temp is stored as
       // 14.2 fixed point.
       return (analog_read(i) * 500L) >> 8;
-
-    case 0:  // IDLE
-    default:
-      temp_sensors_runtime[i].active = 0;
-      return 0;
   }
+  return TEMP_NOT_READY;
 }
 #endif /* TEMP_AD595 */
 
 #ifdef TEMP_INTERCOM
 static uint16_t temp_read_intercom(temp_sensor_t i) {
-  temp_sensors_runtime[i].active = 0;
+  switch (temp_sensors_runtime[i].active++) {
-  return read_temperature(temp_sensors[i].temp_pin);
+    case 1:
+      return read_temperature(temp_sensors[i].temp_pin);
+    case 25:  // Idle for 250ms.
+      temp_sensors_runtime[i].active = 0;
+  }
+  return TEMP_NOT_READY;
 }
 #endif /* TEMP_INTERCOM */
 
 #ifdef TEMP_DUMMY
+static uint16_t dummy_temp[NUM_TEMP_SENSORS];
+
 static uint16_t temp_read_dummy(temp_sensor_t i) {
-  uint16_t temp = temp_sensors_runtime[i].last_read_temp;
+  if (temp_sensors_runtime[i].target_temp > dummy_temp[i])
+    dummy_temp[i]++;
+  else if (temp_sensors_runtime[i].target_temp < dummy_temp[i])
+    dummy_temp[i]--;
 
-  temp_sensors_runtime[i].active = 0;
+  switch (temp_sensors_runtime[i].active++) {
-
+    case 1:
-  if (temp_sensors_runtime[i].target_temp > temp)
+      return dummy_temp[i] ;
-    temp++;
+    case 5:  // Idle for 50ms.
-  else if (temp_sensors_runtime[i].target_temp < temp)
+      temp_sensors_runtime[i].active = 0;
-    temp--;
+  }
-
+  return TEMP_NOT_READY;
-  return temp;
 }
 #endif /* TEMP_DUMMY */
 
@@ -395,6 +420,14 @@ static uint16_t read_temp_sensor(temp_sensor_t i) {
   }
 }
 
+static void run_pid_loop(int i) {
+  if (temp_sensors[i].heater < NUM_HEATERS) {
+    heater_tick(temp_sensors[i].heater, temp_sensors[i].temp_type,
+                temp_sensors_runtime[i].last_read_temp,
+                temp_sensors_runtime[i].target_temp);
+  }
+}
+
 /**
   Called every 10ms from clock.c. Check all temp sensors that are ready for
   checking. When complete, update the PID loop for sensors tied to heaters.
@@ -403,29 +436,30 @@ void temp_sensor_tick() {
 	temp_sensor_t i = 0;
 
 	for (; i < NUM_TEMP_SENSORS; i++) {
+    if (TEMP_READ_CONTINUOUS)
+      if ( ! temp_sensors_runtime[i].active)
+        temp_sensors_runtime[i].active = 1;
+
     if (temp_sensors_runtime[i].active) {
       uint16_t temp = read_temp_sensor(i);
 
-      // Ignore temperature value if sensor read is still active.
+      if (temp == TEMP_NOT_READY)
-      if (temp_sensors_runtime[i].active)
         continue;
 
-			/* Exponentially Weighted Moving Average alpha constant for smoothing
+      // Handle moving average.
-			   noisy sensors. Instrument Engineer's Handbook, 4th ed, Vol 2 p126
+      temp_sensors_runtime[i].last_read_temp = (uint16_t)(
-			   says values of 0.05 to 0.1 for TEMP_EWMA are typical. */
+        (EWMA_ALPHA * temp +
-			#define EWMA_SCALE  1024L
+         (EWMA_SCALE - EWMA_ALPHA) * temp_sensors_runtime[i].last_read_temp) /
-			#define EWMA_ALPHA  ((long) (TEMP_EWMA * EWMA_SCALE))
+        EWMA_SCALE);
-			temp_sensors_runtime[i].last_read_temp = (uint16_t) ((EWMA_ALPHA * temp +
-			  (EWMA_SCALE-EWMA_ALPHA) * temp_sensors_runtime[i].last_read_temp
-			                                         ) / EWMA_SCALE);
 
-      // Finished reading this temperature probe. Update heater PID loop.
+      if ( ! TEMP_READ_CONTINUOUS) {
-      // This must only be done four times per second to keep the PID values
+        /**
-      // sane.
+          In one-shot mode we only update temps when triggered by the
-      if (temp_sensors[i].heater < NUM_HEATERS) {
+          heater_tick for PID loops. So here we run the PID loop through a
-        heater_tick(temp_sensors[i].heater, temp_sensors[i].temp_type,
+          cycle. This must only be done four times per second to keep the PID
-                    temp_sensors_runtime[i].last_read_temp,
+          values sane.
-                    temp_sensors_runtime[i].target_temp);
+        */
+        run_pid_loop(i);
       }
     }
   }
@@ -437,9 +471,14 @@ void temp_sensor_tick() {
 void temp_heater_tick() {
   temp_sensor_t i;
 
-  // Signal all the temperature probes to begin reading.
   for (i = 0; i < NUM_TEMP_SENSORS; i++)
-    temp_sensors_runtime[i].active = 1;
+    if (TEMP_READ_CONTINUOUS)
+      run_pid_loop(i);
+    else {
+      // Signal all the temperature probes to begin reading. Each will run the
+      // pid loop for us when it completes.
+      temp_sensors_runtime[i].active = 1;
+    }
 }
 
 /**