Max31855: stop using SPI from ISR

src/modules/tools/temperaturecontrol/TempSensor.h

@@ -26,6 +26,7 @@ class TempSensor
     virtual bool set_optional(const sensor_options_t& options) { return false; }
     virtual bool get_optional(sensor_options_t& options) { return false; }
     virtual void get_raw() {}
+    virtual void on_idle() {}
 };
 
 #endif

src/modules/tools/temperaturecontrol/TemperatureControl.cpp

@@ -103,6 +103,7 @@ void TemperatureControl::on_module_loaded()
         this->register_for_event(ON_MAIN_LOOP);
         this->register_for_event(ON_SET_PUBLIC_DATA);
         this->register_for_event(ON_HALT);
+        this->register_for_event(ON_IDLE);
     }
 }
 
@@ -116,6 +117,12 @@ void TemperatureControl::on_halt(void *arg)
     }
 }
 
+void TemperatureControl::on_idle(void *arg)
+{
+    sensor->on_idle();
+}
+
+
 void TemperatureControl::on_main_loop(void *argument)
 {
     if (this->temp_violated) {

src/modules/tools/temperaturecontrol/TemperatureControl.h

@@ -26,6 +26,7 @@ class TemperatureControl : public Module {
         void on_get_public_data(void* argument);
         void on_set_public_data(void* argument);
         void on_halt(void* argument);
+        void on_idle(void* argument);
 
         void set_desired_temperature(float desired_temperature);
 

src/modules/tools/temperaturecontrol/max31855.cpp

@@ -22,6 +22,7 @@
 Max31855::Max31855() :
     spi(nullptr)
 {
+    this->read_flag=true;
 }
 
 Max31855::~Max31855()
@@ -57,40 +58,36 @@ void Max31855::UpdateConfig(uint16_t module_checksum, uint16_t name_checksum)
     spi->format(16);
 }
 
+// returns an average of the last few temperature values we've read
 float Max31855::get_temperature()
 {
-	// Return an average of the last readings
-    if (readings.size() >= readings.capacity()) {
-        readings.delete_tail();
-    }
-
-	float temp = read_temp();
+    // allow read from hardware via SPI on next call to on_idle()
+    this->read_flag=true;
 
-	// Discard occasional errors...
-	if(!isinf(temp))
-	{
-		readings.push_back(temp);
-	}
+    // Return an average of the last readings
+    if(readings.size()==0) return infinityf();
 
-	if(readings.size()==0) return infinityf();
-
-	float sum = 0;
+    float sum = 0;
     for (int i=0; i<readings.size(); i++) {
         sum += *readings.get_ref(i);
     }
 
-	return sum / readings.size();
+    return sum / readings.size();
 }
 
-float Max31855::read_temp()
+// ask the temperature sensor hardware for a value, store it in a buffer
+void Max31855::on_idle()
 {
+    // this rate limits SPI access
+    if(!this->read_flag) return;
+
     this->spi_cs_pin.set(false);
     wait_us(1); // Must wait for first bit valid
 
     // Read 16 bits (writing something as well is required by the api)
     uint16_t data = spi->write(0);
-	//  Read next 16 bits (diagnostics)
-//	uint16_t data2 = spi->write(0);
+    //  Read next 16 bits (diagnostics)
+    //	uint16_t data2 = spi->write(0);
 
     this->spi_cs_pin.set(true);
 
@@ -114,5 +111,17 @@ float Max31855::read_temp()
             temperature = ((data & 0x1FFF) + 1) / -4.f;
         }
     }
-    return temperature;
+
+    if (readings.size() >= readings.capacity()) {
+        readings.delete_tail();
+    }
+
+    // Discard occasional errors...
+    if(!isinf(temperature))
+    {
+        readings.push_back(temperature);
+    }
+
+    // don't read again until get_temperature() is called
+    this->read_flag=false;
 }

src/modules/tools/temperaturecontrol/max31855.h

@@ -21,9 +21,10 @@ class Max31855 : public TempSensor
     ~Max31855();
     void UpdateConfig(uint16_t module_checksum, uint16_t name_checksum);
     float get_temperature();
+    void on_idle();
 
 private:
-	float read_temp();
+    struct { bool read_flag:1; } ; //when true, the next call to on_idle will read a new temperature value
     Pin spi_cs_pin;
     mbed::SPI *spi;
     RingBuffer<float,16> readings;