Implement control loop

src/fan_controller.c

@@ -0,0 +1,131 @@
+#include "fan_controller.h"
+
+/*
+ * The control loop is based on a temperature corridor concept. While the
+ * temperature is inside the corridor, the PWM duty cycle will not be changed.
+ *
+ * If it is above the corridor’s maximum temperature, the duty cycle increases
+ * as defined by a PI controller, i.e. there is a dynamic/temporary part (P)
+ * that depends on how far outside the corridor the temperature is, and there
+ * is a persistent part (I) that is continuously increased while the
+ * temperature is outside the corridor.
+ *
+ * If the temperature is below the corridor’s minimum temperature, similar
+ * rules are applied to decrease the fan speed. However, the P part makes
+ * little sense here so its gain is usually set to 0.
+ *
+ * The fan starts in a stopped state and stays there until the temperature
+ * rises above the startup temperature. Once that happens, the PWM is set
+ * to a specific duty cycle (high enough to reliably start the fan) and
+ * regulation begins.
+ */
+
+/* Note:
+ * - all temperatures are in °C represented in fxp_t.
+ * - all duty cycles are in percent represented in fxp_t.
+ */
+
+// corridor definition
+#define CORRIDOR_MIN_TEMPERATURE     (40 << POINTPOS)
+#define CORRIDOR_MAX_TEMPERATURE     (45 << POINTPOS)
+
+// The fan is started when temperature rises above this temperature.
+#define FAN_START_TEMPERATURE        (42 << POINTPOS)
+
+// The fan is stopped when the temperature falls below this point.
+#define FAN_OFF_TEMPERATURE          (30 << POINTPOS)
+
+// Emergency temperature level. If this is reached, the duty cycle is directly
+// set to the maximum to skip a long ramp-up phase.
+#define EMERGENCY_TEMPERATURE        (60 << POINTPOS)
+
+// The fan PWM duty cycle cannot fall below this limit. It is held until
+// temperature falls below the off-temperature.
+#define DUTY_CYCLE_MIN     (5 << POINTPOS)
+
+// The fan PWM duty cycle cannot go above this limit. Should be set to 100.
+#define DUTY_CYCLE_MAX     (100 << POINTPOS)
+
+// The fan is always started with this duty cycle. Do not set too low.
+#define DUTY_CYCLE_START   (20 << POINTPOS)
+
+// gain unit: percent duty cycle change per °C deviation per update cycle
+#define GAIN_T_HIGH_P      0x00020000   // 2.000
+#define GAIN_T_HIGH_I      0x00002000   // 0.125
+#define GAIN_T_LOW_P       0x00000000   // 0.000
+#define GAIN_T_LOW_I       0x00002000   // 0.125
+//                 integer unit ^
+
+static fxp_t m_duty;
+
+void fan_controller_init(void)
+{
+	m_duty = 0; // fan off by default
+}
+
+
+uint8_t fan_controller_update(fxp_t temperature)
+{
+	fxp_t duty_out = m_duty;
+
+	// check emergency case. Directly starts the fan, if necessary.
+	if(temperature > EMERGENCY_TEMPERATURE) {
+		m_duty = duty_out = DUTY_CYCLE_MAX;
+	}
+
+	if(m_duty == 0) {
+		// we are currently in off state. Check whether we need to start.
+		if(temperature > FAN_START_TEMPERATURE) {
+			m_duty = duty_out = DUTY_CYCLE_START;
+		}
+	} else {
+		// fan is currently on
+
+		// corridor handling: too warm
+		if(temperature > CORRIDOR_MAX_TEMPERATURE) {
+			fxp_t delta_above = fxp_sub(temperature, CORRIDOR_MAX_TEMPERATURE);
+
+			fxp_t duty_p = fxp_mult(delta_above, GAIN_T_HIGH_P);
+			fxp_t duty_i = fxp_mult(delta_above, GAIN_T_HIGH_I);
+
+			m_duty = fxp_add(m_duty, duty_i);
+
+			if(m_duty > DUTY_CYCLE_MAX) {
+				m_duty = DUTY_CYCLE_MAX;
+			}
+
+			duty_out = fxp_add(m_duty, duty_p);
+
+			if(duty_out > DUTY_CYCLE_MAX) {
+				duty_out = DUTY_CYCLE_MAX;
+			}
+		}
+
+		// corridor handling: too cold
+		if(temperature < CORRIDOR_MIN_TEMPERATURE) {
+			fxp_t delta_below = fxp_sub(temperature, CORRIDOR_MIN_TEMPERATURE);
+
+			fxp_t duty_p = fxp_mult(delta_below, GAIN_T_LOW_P);
+			fxp_t duty_i = fxp_mult(delta_below, GAIN_T_LOW_I);
+
+			m_duty = fxp_add(m_duty, duty_i);
+
+			if(m_duty < DUTY_CYCLE_MIN) {
+				m_duty = DUTY_CYCLE_MIN;
+			}
+
+			duty_out = fxp_add(m_duty, duty_p);
+
+			if(duty_out < DUTY_CYCLE_MIN) {
+				duty_out = DUTY_CYCLE_MIN;
+			}
+		}
+
+		// fan stop handling
+		if(temperature < FAN_OFF_TEMPERATURE) {
+			m_duty = duty_out = 0;
+		}
+	}
+
+	return FXP_TO_INT(duty_out);
+}

src/fan_controller.h

@@ -0,0 +1,15 @@
+#ifndef FAN_CONTROLLER_H
+#define FAN_CONTROLLER_H
+
+#include <stdint.h>
+#include <fxp.h>
+
+void fan_controller_init(void);
+
+/**@brief Run one iteration of the control loop.
+ * @param temperature   The newly measured temperature in °C.
+ * @returns             The calculated duty cycle.
+ */
+uint8_t fan_controller_update(fxp_t temperature);
+
+#endif // FAN_CONTROLLER_H

src/main.c

@@ -3,8 +3,15 @@
 #include <libopencmsis/core_cm3.h>
 
 #include "uart.h"
+#include "temp_sensor.h"
 #include "fan_ctrl_pwm.h"
 #include "fan_ctrl_dc.h"
+#include "fan_controller.h"
+
+#define SYSTICK_FREQ   10 // Hz
+
+static uint64_t timebase_ms = 0;
+static bool systick_triggered = false;
 
 static void clock_setup(void)
 {
@@ -31,8 +38,6 @@ static void init_systick(int freq)
 
 int main(void)
 {
-	uint64_t timebase_ms = 0;
-
 	// delay startup a bit to allow debugger to connect before debug pins are
 	// reconfigured to UART.
 	for(uint32_t i = 0; i < 1000000; i++) {
@@ -40,16 +45,41 @@ int main(void)
 	}
 
 	clock_setup();
-	init_systick(1000);
+	init_systick(SYSTICK_FREQ);
 
 	uart_init();
+	temp_sensor_init();
+
 	fan_ctrl_pwm_init();
 	fan_ctrl_dc_init();
 
+	fan_controller_init();
+
 	uart_enqueue("TinyFanControl v" VERSION " initialized.\n");
 
+	fan_ctrl_pwm_enable(); // TODO: make DC/PWM configurable
+
 	// triggered every 1 ms
 	while (1) {
+		if(systick_triggered) {
+			systick_triggered = false;
+
+			timebase_ms += 1000 / SYSTICK_FREQ;
+
+			// start the measurement in the background.
+			temp_sensor_trigger_update();
+		}
+
+		// check for completion of a measurement
+		if(temp_sensor_has_new_values()) {
+			// if a temperature update is available, run the control loop.
+			fxp_t temperature = temp_sensor_get_ntc_temperature();
+
+			uint8_t duty = fan_controller_update(temperature);
+
+			fan_ctrl_pwm_set_duty(duty);
+		}
+
 		__WFI();
 	}
 
@@ -60,7 +90,7 @@ int main(void)
 /* Called when systick fires */
 void sys_tick_handler(void)
 {
-	//wait_frame = 0;
+	systick_triggered = true;
 }
 
 

src/temp_sensor.c

@@ -136,7 +136,8 @@ bool temp_sensor_has_new_values(void)
 	if(dma_get_interrupt_flag(DMA1, DMA_CHANNEL1, DMA_TCIF)) {
 		dma_clear_interrupt_flags(DMA1, DMA_CHANNEL1, DMA_TCIF);
 
-		// TODO: calculate temperature values and cache them here.
+		// calculate temperature values and cache them.
+		m_temperature_ntc = calc_temperature_ntc(adc_values[0]);
 		m_temperature_internal = calc_temperature(adc_values[1]);
 		return true;
 	} else {
@@ -147,9 +148,11 @@ bool temp_sensor_has_new_values(void)
 
 fxp_t temp_sensor_get_ntc_temperature(void)
 {
+	return m_temperature_ntc;
 }
 
 
 fxp_t temp_sensor_get_internal_temperature(void)
 {
+	return m_temperature_internal;
 }