Status LED visual feedback for buttons and battery
[heater.git] / firmware / main.c
index 9a04150..76bed47 100644 (file)
@@ -1,3 +1,51 @@
+/*
+ * OVERVIEW
+ *
+ * Powering up:
+ * Immediately after reset, we power down the entire system.
+ * We wake up only after the button is pressed for a sufficiently long time.
+ *
+ * Heater output:
+ * The heater output is driven by Timer/Counter 1 in PWM mode.
+ * We want to be able to measure the battery voltage both when the
+ * output is on, and when the output is off. So we set the T/C1 clock
+ * prescaler so that the T/C1 is slow enough, we enable the T/C1 interrupts
+ * both on compare match and on overflow. After the interrupt, we trigger
+ * the battery voltage measurement with ADC.
+ *
+ * ADC:
+ * To avoid transients, we measure each battery state (when the heater is on
+ * and when it is off) separately, and we drop the first few readings.
+ * We calculate a running average of the readings to achieve higher accuracy.
+ *
+ * Buttons:
+ * There are two buttons (+ and -). Any button can wake the system up from
+ * the power-down state.
+ * TODO: When the system is woken up by the "-" button,
+ * it starts with the minimum output power, when it is woken up by the "+"
+ * button, it start with the maximum output power.
+ * When running, the "-" button is used for decreasing the output power,
+ * the "+" button is for increasing it.
+ * When on the lowest power state, the "-" button switches the system off.
+ * Long "-" button press switches the system off, long "+" button
+ * press sets the output power to maximum.
+ *
+ * Status LED:
+ * When powering up by a button press, the LED goes on to provide a visual
+ * feedback, and is switched off after the button is released.
+ * After a button press, the # of blinks of the LED reflects the
+ * chosen output power level for some time. Afterwards, it displays
+ * the battery level.
+ * When the battery is completely exhausted, the output power is switched
+ * off, the LED keeps blinking for some time, and then the whole system is
+ * switched off to avoid deep discharge of the battery.
+ *
+ * Timing:
+ * The firmware is timed by the Watchdog Timer interrupt. Most of the
+ * processing is done from the main loop, IRQs only set various flags
+ * or trigger other events.
+ */
+
 #include <avr/interrupt.h>
 #include <avr/io.h>
 #include <avr/power.h>
 #include <avr/interrupt.h>
 #include <avr/io.h>
 #include <avr/power.h>
 
 #include "logging.h"
 
 
 #include "logging.h"
 
-static unsigned char pwm = 1;
+/* waking up from the power down state by a button press */
+#define WAKEUP_POLL 50 // msec
+#define WAKEUP_LIMIT 5 // times WAKEUP_POLL
+
+/* which state (output on or output off) are we measuring now */
+static volatile unsigned char adc_type, adc_drop;
+#define ADC_RUNAVG_SHIFT 5     // running average shift on batt_on, batt_off
+static volatile uint16_t batt_on, batt_off; // measured voltage
+
+/*
+ * The voltage divider has 1M5 and 300K resistors (i.e. it measures 1/6th of
+ * the real voltage), ADC uses 1.1V internal reference.
+ * Macro to calculate upper eight bits of the ADC running-averaged value
+ * from the voltage in milivolts.
+ */
+#define ADC_1100MV_VALUE       1071    // measured, not exactly 1100
+#define MV_TO_ADC8(mV) ((unsigned char)(((uint32_t)(1UL << ADC_RUNAVG_SHIFT) \
+                               * (1024UL * (mV)) \
+                               / (6UL * ADC_1100MV_VALUE)) >> 8))
+static unsigned char batt_levels[] = {
+       MV_TO_ADC8(3350),
+       MV_TO_ADC8(3700),
+       MV_TO_ADC8(3900),
+};
+#define BATT_N_LEVELS  (sizeof(batt_levels) / sizeof(batt_levels[0]))
+
+/* output power and PWM calculation */
+#define PWM_TOP        255
+#define PWM_MAX        (PWM_TOP - 8)   // to allow for ADC "batt_off" measurements
+
+/*
+ * The values in power_levels[] array are voltages at which the load
+ * would give the expected power (we don't have sqrt() function,
+ * so we cannot use mW values directly. They can be calculated as
+ * voltage[V] = sqrt(load_resistance[Ohm] * expected_power[W])
+ * or
+ * voltage[mV] = sqrt(load_resistance[mOhm] * expected_power[mW])
+ *
+ * I use 1.25 W as minimum power, each step is sqrt(2)*previous_step,
+ * so the 5th step is 5 W.
+ */
+static unsigned char power_levels[] = {
+       MV_TO_ADC8(1581),       // 1250 mW for 2 Ohm load
+       MV_TO_ADC8(1880),       // 1768 mW for 2 Ohm load
+       MV_TO_ADC8(2236),       // 2500 mW for 2 Ohm load
+       MV_TO_ADC8(2659),       // 3536 mW for 2 Ohm load
+       MV_TO_ADC8(3162),       // 5000 mW for 2 Ohm load
+};
+#define N_POWER_LEVELS (sizeof(power_levels) / sizeof(power_levels[0]))
+
+static unsigned char power_level = 0; // selected power level
+static unsigned char power_level_changed; // for visual feedback
+
+#define LED_PWRCHANGE_COUNT    3
+#define LED_BATTEMPTY_COUNT    60
+
+/* timing by WDT */
+static volatile unsigned char jiffies, next_clock_tick;
+
+/* button press duration (in jiffies) */
+#define BUTTON_SHORT_MIN       1
+#define BUTTON_LONG_MIN                10
+
+
+/* ========= Analog to Digital Converter (battery voltage) ========== */
+static void adc_init()
+{
+       power_adc_enable();
+
+       ADCSRA = _BV(ADEN)                      // enable
+               | _BV(ADPS1) | _BV(ADPS0)       // clk/8 = 125 kHz
+               | _BV(ADIE);                    // enable IRQ
+       ADMUX = _BV(REFS1) | _BV(MUX1) | _BV(MUX0);
+               // 1.1V reference, PB3 pin, single-ended
+       DIDR0 |= _BV(ADC3D);    // PB3 pin as analog input
+}
+
+static void adc_susp()
+{
+       ADCSRA &= ~_BV(ADEN);   // disable ADC
+       DIDR0 &= ~_BV(ADC3D);   // disable analog input on PB3
+
+       power_adc_disable();
+}
+
+static void adc_start_measurement()
+{
+       ADCSRA |= _BV(ADSC);
+}
+
+ISR(ADC_vect)
+{
+       uint16_t adcw = ADCW;
+
+       if (adc_drop) {
+               adc_drop--;
+               ADCSRA |= _BV(ADSC);
+               return;
+       }
+
+       // TODO: We may want to disable ADC after here to save power,
+       // but compared to the heater power it would be negligible,
+       // so don't bother with it.
+       if (adc_type == 0) {
+               if (batt_off) {
+                       batt_off += adcw - (batt_off >> ADC_RUNAVG_SHIFT);
+               } else {
+                       batt_off = adcw << ADC_RUNAVG_SHIFT;
+               }
+       } else {
+               if (batt_on) {
+                       batt_on += adcw - (batt_on >> ADC_RUNAVG_SHIFT);
+               } else {
+                       batt_on = adcw << ADC_RUNAVG_SHIFT;
+               }
+       }
+}
 
 
-static void timer_init()
+/* ===================== Timer/Counter1 for PWM ===================== */
+static void pwm_init()
 {
        power_timer1_enable();
 
        DDRB |= _BV(PB4);
 
 {
        power_timer1_enable();
 
        DDRB |= _BV(PB4);
 
-       TCCR1 = _BV(CS10); // clk/1 = 1 MHz
-       // TCCR1 = _BV(CS11) | _BV(CS13); // clk/512 = 2 kHz
+       // TCCR1 = _BV(CS10); // clk/1 = 1 MHz
+       TCCR1 = _BV(CS11) | _BV(CS13); // clk/512 = 2 kHz
        GTCCR = _BV(COM1B1) | _BV(PWM1B);
        GTCCR = _BV(COM1B1) | _BV(PWM1B);
-       OCR1C = 255;
-       OCR1B = pwm;
+       OCR1C = PWM_TOP;
+       // OCR1B = steps[0];
+       OCR1B = 0;
+       TIMSK = _BV(OCIE1B) | _BV(TOIE1);
 }
 
 }
 
-static void adc_init()
+static void pwm_susp()
 {
 {
-       power_adc_enable();
+       TCCR1 = 0;
+}
+
+ISR(TIM1_OVF_vect)
+{
+       adc_drop = 2;
+       adc_type = 1;
+       adc_start_measurement();
+}
+
+ISR(TIM1_COMPB_vect)
+{
+       adc_drop = 2;
+       adc_type = 0;
+       adc_start_measurement();
+}
 
 
-       ADCSRA = _BV(ADEN) | _BV(ADPS1) | _BV(ADPS0); // clk/8 = 125 kHz
-       ADMUX = _BV(REFS1) | _BV(MUX1) | _BV(MUX0); // 1.1V ref., PB3 single-ended
-       DIDR0 = _BV(ADC3D);
+static void pwm_set(unsigned char pwm)
+{
+       OCR1B = pwm;
 }
 
 }
 
+/* ===================== Status LED on pin PB2 ======================= */
 static void status_led_init()
 {
        DDRB |= _BV(PB2);
 static void status_led_init()
 {
        DDRB |= _BV(PB2);
@@ -47,6 +230,12 @@ static void status_led_off()
        PORTB &= ~_BV(PB2);
 }
 
        PORTB &= ~_BV(PB2);
 }
 
+static unsigned char status_led_is_on()
+{
+       return PORTB & _BV(PB2) ? 1 : 0;
+}
+
+/* ================== Buttons on pin PB0 and PB1 ===================== */
 static void buttons_init()
 {
        DDRB &= ~(_BV(PB0) | _BV(PB1)); // set as input
 static void buttons_init()
 {
        DDRB &= ~(_BV(PB0) | _BV(PB1)); // set as input
@@ -73,9 +262,6 @@ static unsigned char buttons_pressed()
        );
 }
 
        );
 }
 
-#define WAKEUP_POLL 100        // msec
-#define WAKEUP_LIMIT 5 // times WAKEUP_POLL
-
 static unsigned char buttons_wait_for_release()
 {
        uint16_t wake_count = 0;
 static unsigned char buttons_wait_for_release()
 {
        uint16_t wake_count = 0;
@@ -97,8 +283,11 @@ ISR(PCINT0_vect)
         // empty - let it wake us from sleep, but do nothing else
 }
 
         // empty - let it wake us from sleep, but do nothing else
 }
 
+/* ==== Watchdog Timer for timing blinks and other periodic tasks ==== */
 static void wdt_init()
 {
 static void wdt_init()
 {
+       next_clock_tick = 0;
+       jiffies = 0;
        WDTCR = _BV(WDIE) | _BV(WDP1); // interrupt mode, 64 ms
 }
 
        WDTCR = _BV(WDIE) | _BV(WDP1); // interrupt mode, 64 ms
 }
 
@@ -107,11 +296,17 @@ static void wdt_susp()
        wdt_disable();
 }
 
        wdt_disable();
 }
 
+ISR(WDT_vect) {
+       next_clock_tick = 1;
+       jiffies++;
+}
+
+/* ====== Hardware init, teardown, powering down and waking up ====== */
 static void hw_setup()
 {
        power_all_disable();
 
 static void hw_setup()
 {
        power_all_disable();
 
-       timer_init();
+       pwm_init();
        adc_init();
        status_led_init();
        wdt_init();
        adc_init();
        status_led_init();
        wdt_init();
@@ -119,22 +314,15 @@ static void hw_setup()
 
 static void hw_suspend()
 {
 
 static void hw_suspend()
 {
-       ADCSRA &= ~_BV(ADEN); // disable ADC
-       TCCR1 = 0; // disable T/C 1
-
-       status_led_init();
+       adc_susp();
+       pwm_susp();
+       status_led_init(); // we don't have a separate _susp() here
        buttons_susp();
        wdt_susp();
 
        power_all_disable();
 }
 
        buttons_susp();
        wdt_susp();
 
        power_all_disable();
 }
 
-static volatile unsigned char wdt_timer_fired;
-
-ISR(WDT_vect) {
-       wdt_timer_fired = 1;
-}
-
 static void power_down()
 {
        hw_suspend();
 static void power_down()
 {
        hw_suspend();
@@ -158,22 +346,97 @@ static void power_down()
        hw_setup();
 }
 
        hw_setup();
 }
 
-static void button_one_pressed()
+/* ============ Status LED blinking =================================== */
+static unsigned char blink_on_time, blink_off_time, n_blinks;
+static unsigned char blink_counter;
+
+static unsigned char battery_level()
+{
+       unsigned char i, adc8;
+
+       // NOTE: we use 8-bit value only, so we don't need lock to protect
+       // us against concurrently running ADC IRQ handler:
+       adc8 = batt_off >> 8;
+
+       for (i = 0; i < BATT_N_LEVELS; i++)
+               if (batt_levels[i] > adc8)
+                       break;
+
+       return i;
+}
+
+static void status_led_next_pattern()
 {
 {
-       if (pwm > 1) {
-               pwm >>= 1;
-               OCR1B = pwm;
+       static unsigned char battery_exhausted;
+
+       if (power_level_changed) {
+               power_level_changed--;
+               n_blinks = power_level + 1;
+       } else {
+               unsigned char b_level = battery_level();
+               if (b_level) {
+                       battery_exhausted = 0;
+               } else if (battery_exhausted) {
+                       if (!--battery_exhausted)
+                               power_down();
+               } else {
+                       battery_exhausted = LED_BATTEMPTY_COUNT;
+               }
+
+               n_blinks = b_level + 1;
+       }
+
+       blink_on_time = 2;
+       blink_off_time = 1;
+       blink_counter = 10;
+}
+
+static void timer_blink()
+{
+       if (blink_counter) {
+               blink_counter--;
+       } else if (!status_led_is_on()) {
+               status_led_on();
+               blink_counter = blink_on_time;
+       } else if (n_blinks) {
+               --n_blinks;
+               status_led_off();
+               blink_counter = blink_off_time;
        } else {
        } else {
-               power_down();
+               status_led_next_pattern();
        }
 }
 
        }
 }
 
-static void button_two_pressed()
+/* ======== Button press detection and  handling ===================== */
+static void button_pressed(unsigned char button, unsigned char long_press)
 {
 {
-       if (pwm < 0x80) {
-               pwm <<= 1;
-               OCR1B = pwm;
+       // ignore simlultaneous button 1 and 2 press
+       // Note: we set power_level_changed after each button press,
+       // even when the power is at maximum, to provide visual feedback
+       // with status LED.
+       if (long_press) {
+               if (button == 1) {
+                       power_down();
+                       return;
+               } else if (button == 2) {
+                       power_level = N_POWER_LEVELS-1;
+               }
+       } else { // short press
+               if (button == 1) {
+                       if (power_level > 0) {
+                               --power_level;
+                       } else {
+                               power_down();
+                               return;
+                       }
+               } else if (button == 2) {
+                       if (power_level < N_POWER_LEVELS-1) {
+                               ++power_level;
+                       }
+               }
        }
        }
+       power_level_changed = LED_PWRCHANGE_COUNT;
+       status_led_next_pattern();
 }
 
 static unsigned char button_state, button_state_time;
 }
 
 static unsigned char button_state, button_state_time;
@@ -183,8 +446,12 @@ static void timer_check_buttons()
        unsigned char newstate = buttons_pressed();
 
        if (newstate == button_state) {
        unsigned char newstate = buttons_pressed();
 
        if (newstate == button_state) {
-               if (newstate && button_state_time < 4)
+               if (newstate && button_state_time < BUTTON_LONG_MIN)
                        ++button_state_time;
                        ++button_state_time;
+
+               if (newstate && button_state_time >= BUTTON_LONG_MIN) {
+                       status_led_on();
+               }
                return;
        }
 
                return;
        }
 
@@ -195,35 +462,58 @@ static void timer_check_buttons()
        }
 
        // just released
        }
 
        // just released
-       switch (button_state) {
-       case 1: button_one_pressed();
-               break;
-       case 2: button_two_pressed();
-               break;
-       default: // ignore when both are preseed
-               break;
-       }
+       if (button_state_time >= BUTTON_SHORT_MIN)
+               button_pressed(button_state,
+                       button_state_time >= BUTTON_LONG_MIN ? 1 : 0);
 
        button_state = newstate;
 
        button_state = newstate;
+       button_state_time = 0;
+}
+
+/* ===================== Output power control ======================== */
+static void calculate_power_level()
+{
+       uint32_t pwm;
+       unsigned char batt_on8;
+
+       if (battery_level() == 0 || batt_on == 0) {
+               pwm_set(0);
+               // TODO power_down() after some time
+               return;
+       }
+
+       batt_on8 = batt_on >> 8;
+
+       pwm = (uint32_t)PWM_TOP * power_levels[power_level]
+               * power_levels[power_level];
+       pwm /= (uint32_t)batt_on8 * batt_on8;
+
+       if (pwm > PWM_MAX)
+               pwm = PWM_MAX;
+
+       log_byte(0x10 + power_level);
+       log_byte(batt_on8);
+       log_byte(pwm & 0xFF);
+
+       pwm_set(pwm);
 }
 
 int main()
 {
        log_init();
 
 }
 
 int main()
 {
        log_init();
 
-       power_down();
-
 #if 0
 #if 0
-       ADCSRA |= _BV(ADSC);
-       while (!(ADCSRA & _BV(ADIF)))
-               ;
-       log_word(ADCW);
-       ADCSRA |= _BV(ADSC);
-       while (!(ADCSRA & _BV(ADIF)))
-               ;
-       log_word(ADCW);
+       log_word(batt_levels[0]);
+       log_word(batt_levels[1]);
+       log_word(batt_levels[2]);
        log_flush();
 #endif
        log_flush();
 #endif
+       log_byte(power_levels[0]);
+       log_byte(power_levels[4]);
+       log_flush();
+
+       power_down();
+
        sei();
 
        // we try to be completely IRQ-driven, so just wait for IRQs here
        sei();
 
        // we try to be completely IRQ-driven, so just wait for IRQs here
@@ -236,9 +526,24 @@ int main()
                sleep_cpu();
                sleep_disable();
 
                sleep_cpu();
                sleep_disable();
 
-               if (wdt_timer_fired) {
-                       wdt_timer_fired = 0;
+               // FIXME: Maybe handle new ADC readings as well?
+               if (next_clock_tick) {
+                       next_clock_tick = 0;
+                       timer_blink();
+                       // this has to be after the timer_blink() call
+                       // to override the status LED during long button press
                        timer_check_buttons();
                        timer_check_buttons();
+
+                       if ((jiffies & 0x0F) == 0) {
+                               calculate_power_level();
+#if 0
+                               log_byte(0xcc);
+                               log_byte(i);
+                               log_byte(batt_off >> 8);
+                               log_byte(batt_on >> 8);
+#endif
+                       }
+                       log_flush();
                }
        }
 }
                }
        }
 }