--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.c	Sat Jun 01 01:38:42 2013 +0800
@@ -0,0 +1,1200 @@
+#include <stdio.h>
+#include <string.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <avr/sleep.h>
+#include <util/delay.h>
+#include <avr/pgmspace.h>
+#include <avr/eeprom.h>
+#include <avr/wdt.h>
+#include <util/atomic.h>
+#include <util/crc16.h>
+
+#include "simple_ds18b20.h"
+#include "onewire.h"
+
+// configuration params
+// - measurement interval
+// - transmit interval
+// - bluetooth params
+// - number of sensors (and range?)
+
+#define MIN(X,Y) ((X) < (Y) ? (X) : (Y))
+#define MAX(X,Y) ((X) > (Y) ? (X) : (Y))
+
+// TICK should be 8 or less (8 untested). all timers need
+// to be a multiple.
+
+#define TICK 6
+// we have 1024 prescaler, 32768 crystal.
+#define SLEEP_COMPARE (32*TICK-1)
+
+#define VALUE_NOSENSOR 0x07D0 // 125 degrees
+#define VALUE_BROKEN 0x07D1 // 125.0625
+
+#define OVERSHOOT_MAX_DIV 1800.0 // 30 mins
+#define WORT_INVALID_TIME 900 // 15 mins
+// fridge min/max are only used if the wort sensor is invalid
+#define FRIDGE_AIR_MIN_RANGE 40 // 4º
+#define FRIDGE_AIR_MAX_RANGE 40 // 4º
+
+#define BAUD 19200
+#define UBRR ((F_CPU)/8/(BAUD)-1)
+
+#define PORT_LED PORTC
+#define DDR_LED DDRC
+#define PIN_LED PC4
+
+#define PORT_SHDN PORTD
+#define DDR_SHDN DDRD
+#define PIN_SHDN PD7
+
+#define PORT_FRIDGE PORTD
+#define DDR_FRIDGE DDRD
+#define PIN_FRIDGE PD6
+
+// total amount of 16bit values available for measurements.
+// adjust emperically, be sure to allow enough stack space too
+#define TOTAL_MEASUREMENTS 800
+
+// each sensor slot uses 8 bytes
+#define MAX_SENSORS 6
+
+// fixed at 8, have a shorter name
+#define ID_LEN OW_ROMCODE_SIZE
+
+// #define HAVE_UART_ECHO
+
+// stores a value of clock_epoch combined with the remainder of TCNT2,
+// for 1/32 second accuracy
+struct epoch_ticks
+{
+    uint32_t ticks;
+    // remainder
+    uint8_t rem;
+};
+
+// eeprom-settable parameters. all timeouts should
+// be a multiple of TICK (6 seconds probably)
+static uint16_t measure_wake = 61; // not a divisor of comms_wake
+static uint16_t comms_wake = 600;
+static uint8_t wake_secs = 30;
+// decidegrees
+static int16_t fridge_setpoint = 180; // 18.0ºC
+static uint16_t fridge_difference = 3; // 0.3ºC
+static uint16_t fridge_delay = 600; // seconds
+
+static uint16_t overshoot_delay = 720; // 12 mins
+static uint8_t overshoot_factor = 10; // 1.0ºC
+
+// ---- Atomic guards required accessing these variables
+// clock_epoch in seconds
+static uint32_t clock_epoch;
+static uint16_t comms_count;
+static uint16_t measure_count;
+// ---- End atomic guards required
+
+static uint16_t n_measurements;
+
+// calculated at startup as TOTAL_MEASUREMENTS/n_sensors
+static uint16_t max_measurements;
+
+static uint16_t measurements[TOTAL_MEASUREMENTS];
+
+static struct epoch_ticks first_measurement_clock;
+// last_measurement_clock is redundant but checks that we're not missing
+// samples
+static struct epoch_ticks last_measurement_clock;
+static struct epoch_ticks last_comms_clock;
+
+// boolean flags
+static uint8_t need_measurement;
+static uint8_t need_comms;
+static uint8_t uart_enabled;
+static uint8_t stay_awake;
+static uint8_t button_pressed;
+
+// counts down from WAKE_SECS to 0, goes to deep sleep when hits 0
+static uint8_t comms_timeout;
+
+static uint8_t readpos;
+static char readbuf[30];
+static uint8_t have_cmd;
+
+static uint8_t n_sensors;
+static uint8_t sensor_id[MAX_SENSORS][ID_LEN];
+
+static int16_t last_fridge = DS18X20_INVALID_DECICELSIUS;
+static int16_t last_wort = DS18X20_INVALID_DECICELSIUS;
+static struct epoch_ticks fridge_off_clock = {0};
+static struct epoch_ticks fridge_on_clock = {0};
+static struct epoch_ticks wort_valid_clock = {0};
+
+int uart_putchar(char c, FILE *stream);
+static void long_delay(int ms);
+static void blink();
+static uint16_t adc_vcc();
+
+static FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL,
+        _FDEV_SETUP_WRITE);
+
+static uint16_t crc_out;
+static FILE _crc_stdout = FDEV_SETUP_STREAM(uart_putchar, NULL,
+        _FDEV_SETUP_WRITE);
+// convenience
+static FILE *crc_stdout = &_crc_stdout;
+
+
+// thanks to http://projectgus.com/2010/07/eeprom-access-with-arduino/
+#define eeprom_read_to(dst_p, eeprom_field, dst_size) eeprom_read_block((dst_p), (void *)offsetof(struct __eeprom_data, eeprom_field), (dst_size))
+#define eeprom_read(dst, eeprom_field) eeprom_read_to((&dst), eeprom_field, sizeof(dst))
+#define eeprom_write_from(src_p, eeprom_field, src_size) eeprom_write_block((src_p), (void *)offsetof(struct __eeprom_data, eeprom_field), (src_size))
+#define eeprom_write(src, eeprom_field) { eeprom_write_from(&src, eeprom_field, sizeof(src)); }
+
+#define EXPECT_MAGIC 0x67c9
+
+struct __attribute__ ((__packed__)) __eeprom_data {
+    uint16_t measure_wake;
+    uint16_t comms_wake;
+    uint8_t wake_secs;
+
+    int16_t fridge_setpoint; // decidegrees
+    uint16_t fridge_difference; // decidegrees
+    uint16_t fridge_delay;
+
+    uint16_t overshoot_delay;
+    uint8_t overshoot_factor; // decidegrees
+
+#if 0
+    static uint8_t wort_id[ID_LEN];
+    static uint8_t fridge_id[ID_LEN];
+#endif
+
+    uint16_t magic;
+};
+
+static const uint8_t fridge_id[ID_LEN] = 
+    {0x28,0xCE,0xB2,0x1A,0x03,0x00,0x00,0x99};
+static const uint8_t wort_id[ID_LEN] = 
+    {0x28,0x49,0xBC,0x1A,0x03,0x00,0x00,0x54};
+
+static void deep_sleep();
+
+// 0 or 1
+static uint8_t
+is_fridge_on()
+{
+    if (PORT_FRIDGE & _BV(PIN_FRIDGE))
+    {
+        return 1;
+    }
+    else
+    {
+        return 0;
+    }
+}
+
+// Very first setup
+static void
+setup_chip()
+{
+    cli();
+
+    // stop watchdog timer (might have been used to cause a reset)
+    wdt_reset();
+    MCUSR &= ~_BV(WDRF);
+    WDTCSR |= _BV(WDCE) | _BV(WDE);
+    WDTCSR = 0;
+
+    // Set clock to 2mhz
+    CLKPR = _BV(CLKPCE);
+    // divide by 4
+    CLKPR = _BV(CLKPS1);
+
+    // enable pullups
+    PORTB = 0xff; // XXX change when using SPI
+    PORTD = 0xff;
+    PORTC = 0xff;
+
+    // 3.3v power for bluetooth and SD
+    DDR_LED |= _BV(PIN_LED);
+    DDR_SHDN |= _BV(PIN_SHDN);
+
+    PORT_FRIDGE &= ~_BV(PIN_FRIDGE);
+    DDR_FRIDGE |= _BV(PIN_FRIDGE);
+
+    // set pullup
+    PORTD |= _BV(PD2);
+    // INT0 setup
+    EICRA = (1<<ISC01); // falling edge - data sheet says it won't work?
+    EIMSK = _BV(INT0);
+
+    // comparator disable
+    ACSR = _BV(ACD);
+
+    // disable adc pin input buffers
+    DIDR0 = 0x3F; // acd0-adc5
+    DIDR1 = (1<<AIN1D)|(1<<AIN0D); // ain0/ain1
+
+    sei();
+}
+
+static void
+set_aux_power(uint8_t on)
+{
+    if (on)
+    {
+        PORT_SHDN &= ~_BV(PIN_SHDN);
+    }
+    else
+    {
+        PORT_SHDN |= _BV(PIN_SHDN);
+    }
+}
+
+static void
+get_epoch_ticks(struct epoch_ticks *t)
+{
+    ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+    {
+        t->ticks = clock_epoch;
+        t->rem = TCNT2;
+    }
+}
+
+static void 
+set_measurement(uint8_t sensor, uint16_t measurement, uint16_t reading)
+{
+    measurements[sensor*max_measurements + measurement] = reading;
+}
+
+static uint16_t 
+get_measurement(uint8_t sensor, uint16_t measurement)
+{
+    return measurements[sensor*max_measurements + measurement];
+}
+
+static void
+setup_tick_counter()
+{
+    // set up counter2. 
+    // COM21 COM20 Set OC2 on Compare Match (p116)
+    // WGM21 Clear counter on compare
+    //TCCR2A = _BV(COM2A1) | _BV(COM2A0) | _BV(WGM21);
+    // toggle on match
+    TCCR2A = _BV(COM2A0);
+    // CS22 CS21 CS20  clk/1024
+    TCCR2B = _BV(CS22) | _BV(CS21) | _BV(CS20);
+    // set async mode
+    ASSR |= _BV(AS2);
+    TCNT2 = 0;
+    OCR2A = SLEEP_COMPARE;
+    // interrupt
+    TIMSK2 = _BV(OCIE2A);
+}
+
+static void 
+uart_on()
+{
+    // Power reduction register
+    PRR &= ~_BV(PRUSART0);
+ 
+    // All of this needs to be done each time after turning off the PRR
+    // baud rate
+    UBRR0H = (unsigned char)(UBRR >> 8);
+    UBRR0L = (unsigned char)UBRR;
+    // set 2x clock, improves accuracy of UBRR
+    UCSR0A |= _BV(U2X0);
+    UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0);
+    //8N1
+    UCSR0C = _BV(UCSZ01) | _BV(UCSZ00);
+    uart_enabled = 1;
+}
+
+static void 
+uart_off()
+{
+    // Turn off interrupts and disable tx/rx
+    UCSR0B = 0;
+    uart_enabled = 0;
+
+    // Power reduction register
+    PRR |= _BV(PRUSART0);
+}
+
+int 
+uart_putchar(char c, FILE *stream)
+{
+    if (!uart_enabled)
+    {
+        return EOF;
+    }
+    // XXX could perhaps sleep in the loop for power.
+    if (c == '\n')
+    {
+        loop_until_bit_is_set(UCSR0A, UDRE0);
+        UDR0 = '\r';
+    }
+    loop_until_bit_is_set(UCSR0A, UDRE0);
+    UDR0 = c;
+    if (stream == crc_stdout)
+    {
+        crc_out = _crc_ccitt_update(crc_out, c);
+    }
+    if (c == '\r')
+    {
+        loop_until_bit_is_set(UCSR0A, UDRE0);
+        UDR0 = '\n';
+        if (stream == crc_stdout)
+        {
+            crc_out = _crc_ccitt_update(crc_out, '\n');
+        }
+    }
+    return (unsigned char)c;
+}
+
+static void
+cmd_fetch()
+{
+    crc_out = 0;
+
+    fprintf_P(crc_stdout, PSTR("START\n"));
+    {
+        struct epoch_ticks now;
+        get_epoch_ticks(&now);
+        fprintf_P(crc_stdout, PSTR("now=%lu\n"), now.ticks);
+        fprintf_P(crc_stdout, PSTR("now_rem=%hhu\n"), now.rem);
+    }
+    fprintf_P(crc_stdout, PSTR("time_step=%hu\n"), measure_wake);
+    fprintf_P(crc_stdout, PSTR("first_time=%lu\n"), first_measurement_clock.ticks);
+    fprintf_P(crc_stdout, PSTR("first_time_rem=%hhu\n"), first_measurement_clock.rem);
+    fprintf_P(crc_stdout, PSTR("last_time=%lu\n"),  last_measurement_clock.ticks);
+    fprintf_P(crc_stdout, PSTR("last_time_rem=%hhu\n"),  last_measurement_clock.rem);
+    fprintf_P(crc_stdout, PSTR("comms_time=%lu\n"), last_comms_clock.ticks);
+    fprintf_P(crc_stdout, PSTR("comms_time_rem=%hhu\n"), last_comms_clock.rem);
+    fprintf_P(crc_stdout, PSTR("voltage=%hu\n"), adc_vcc());
+    fprintf_P(crc_stdout, PSTR("measure=%hu\n"), measure_wake);
+    fprintf_P(crc_stdout, PSTR("comms=%hu\n"), comms_wake);
+    fprintf_P(crc_stdout, PSTR("wake=%hhu\n"), wake_secs);
+    fprintf_P(crc_stdout, PSTR("fridge=%.1f\n"), fridge_setpoint/10.0);
+    fprintf_P(crc_stdout, PSTR("fridge_diff=%.1f\n"), fridge_difference/10.0);
+    fprintf_P(crc_stdout, PSTR("fridge_delay=%hu\n"), fridge_delay);
+    fprintf_P(crc_stdout, PSTR("overshoot_factor=%.1f\n"), overshoot_factor/10.0);
+    fprintf_P(crc_stdout, PSTR("overshoot_delay=%hu\n"), overshoot_delay);
+    fprintf_P(crc_stdout, PSTR("fridge_status=%hhu\n"), is_fridge_on());
+    fprintf_P(crc_stdout, PSTR("fridge_last_on=%lu\n"), fridge_on_clock.ticks);
+    fprintf_P(crc_stdout, PSTR("fridge_last_off=%lu\n"), fridge_off_clock.ticks);
+    fprintf_P(crc_stdout, PSTR("last_fridge=%hu\n"), last_fridge);
+    fprintf_P(crc_stdout, PSTR("last_wort=%hu\n"), last_wort);
+    fprintf_P(crc_stdout, PSTR("tick_secs=%d\n"), TICK);
+    fprintf_P(crc_stdout, PSTR("tick_wake=%d\n"), SLEEP_COMPARE);
+    fprintf_P(crc_stdout, PSTR("maxsens=%hhu\n"), MAX_SENSORS);
+    fprintf_P(crc_stdout, PSTR("totalmeas=%hu\n"), TOTAL_MEASUREMENTS);
+    fprintf_P(crc_stdout, PSTR("sensors=%hhu\n"), n_sensors);
+    for (uint8_t s = 0; s < n_sensors; s++)
+    {
+        fprintf_P(crc_stdout, PSTR("sensor_id%hhu="), s);
+        printhex(sensor_id[s], ID_LEN, crc_stdout);
+        fputc('\n', crc_stdout);
+    }
+    fprintf_P(crc_stdout, PSTR("measurements=%hu\n"), n_measurements);
+    for (uint16_t n = 0; n < n_measurements; n++)
+    {
+        fprintf_P(crc_stdout, PSTR("meas%hu="), n);
+        for (uint8_t s = 0; s < n_sensors; s++)
+        {
+            fprintf_P(crc_stdout, PSTR(" %04hx"), get_measurement(s, n));
+        }
+        fputc('\n', crc_stdout);
+    }
+    fprintf_P(crc_stdout, PSTR("END\n"));
+    fprintf_P(stdout, PSTR("CRC=%hu\n"), crc_out);
+}
+
+static void
+cmd_clear()
+{
+    n_measurements = 0;
+    printf_P(PSTR("cleared\n"));
+}
+
+static void
+cmd_btoff()
+{
+    uint8_t rem;
+    uint16_t count_copy;
+    ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+    {
+        count_copy = comms_count;
+        rem = TCNT2;
+    }
+    printf_P(PSTR("next_wake=%hu,"), comms_wake-count_copy);
+    printf_P(PSTR("rem=%hhu,"), rem);
+    printf_P(PSTR("tick_secs=%hhu,"), TICK);
+    printf_P(PSTR("tick_wake=%hhu\n"), SLEEP_COMPARE);
+    _delay_ms(100);
+    comms_timeout = 0;
+    stay_awake = 0;
+}
+
+static void
+cmd_reset()
+{
+    printf_P(PSTR("reset\n"));
+    _delay_ms(100);
+    cli(); // disable interrupts 
+    wdt_enable(WDTO_15MS); // enable watchdog 
+    while(1); // wait for watchdog to reset processor 
+}
+
+static void
+cmd_measure()
+{
+    printf_P(PSTR("measuring\n"));
+    need_measurement = 1;
+}
+
+static void
+cmd_sensors()
+{
+    uint8_t ret = simple_ds18b20_start_meas(NULL);
+    printf_P(PSTR("All sensors, ret %hhu, waiting...\n"), ret);
+    long_delay(DS18B20_TCONV_12BIT);
+    simple_ds18b20_read_all();
+}
+
+static void
+init_sensors()
+{
+    uint8_t id[OW_ROMCODE_SIZE];
+    printf_P(PSTR("init sensors\n"));
+    ow_reset();
+    for( uint8_t diff = OW_SEARCH_FIRST; diff != OW_LAST_DEVICE; )
+    {
+        diff = ow_rom_search( diff, &id[0] );
+        if( diff == OW_PRESENCE_ERR ) {
+            printf_P( PSTR("No Sensor found\r") );
+            return;
+        }
+        
+        if( diff == OW_DATA_ERR ) {
+            printf_P( PSTR("Bus Error\r") );
+            return;
+        }
+
+        if (n_sensors < MAX_SENSORS)
+        {
+            memcpy(sensor_id[n_sensors], id, ID_LEN);
+            printf_P(PSTR("Added sensor %hhu : "), n_sensors);
+            printhex(id, ID_LEN, stdout);
+            putchar('\n');
+            n_sensors++;
+        }
+        else
+        {
+            printf_P(PSTR("Too many sensors\n"));
+        }
+    }
+
+    max_measurements = TOTAL_MEASUREMENTS / n_sensors;
+}
+
+static void
+load_params()
+{
+    uint16_t magic;
+    eeprom_read(magic, magic);
+    if (magic == EXPECT_MAGIC)
+    {
+        eeprom_read(measure_wake, measure_wake);
+        eeprom_read(comms_wake, comms_wake);
+        eeprom_read(wake_secs, wake_secs);
+        eeprom_read(fridge_setpoint, fridge_setpoint);
+        eeprom_read(fridge_difference, fridge_difference);
+        eeprom_read(fridge_delay, fridge_delay);
+        eeprom_read(overshoot_delay, overshoot_delay);
+        eeprom_read(overshoot_factor, overshoot_factor);
+    }
+}
+
+static void
+cmd_get_params()
+{
+    printf_P(PSTR("measure %hu\n"), measure_wake);
+    printf_P(PSTR("comms %hu\n"), comms_wake);
+    printf_P(PSTR("wake %hhu\n"), wake_secs);
+    printf_P(PSTR("tick %d\n"), TICK);
+    printf_P(PSTR("fridge %.1fº\n"), fridge_setpoint / 10.0f);
+    printf_P(PSTR("fridge difference %.1fº\n"), fridge_difference / 10.0f);
+    printf_P(PSTR("fridge_delay %hu\n"), fridge_delay);
+    printf_P(PSTR("overshoot factor %.1fº\n"), overshoot_factor / 10.0f);
+    printf_P(PSTR("overshoot delay %hu\n"), overshoot_delay);
+    printf_P(PSTR("sensors %hhu (%hhu)\n"), 
+            n_sensors, MAX_SENSORS);
+    printf_P(PSTR("meas %hu (%hu)\n"),
+            max_measurements, TOTAL_MEASUREMENTS);
+}
+
+static void
+cmd_set_params(const char *params)
+{
+    uint16_t new_measure_wake;
+    uint16_t new_comms_wake;
+    uint8_t new_wake_secs;
+    int ret = sscanf_P(params, PSTR("%hu %hu %hhu"),
+            &new_measure_wake, &new_comms_wake, &new_wake_secs);
+
+    if (ret != 3)
+    {
+        printf_P(PSTR("Bad values\n"));
+    }
+    else
+    {
+        ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+        {
+            eeprom_write(new_measure_wake, measure_wake);
+            eeprom_write(new_comms_wake, comms_wake);
+            eeprom_write(new_wake_secs, wake_secs);
+            uint16_t magic = EXPECT_MAGIC;
+            eeprom_write(magic, magic);
+        }
+        printf_P(PSTR("set_params for next boot\n"));
+        printf_P(PSTR("measure %hu comms %hu wake %hhu\n"),
+                new_measure_wake, new_comms_wake, new_wake_secs);
+    }
+}
+
+// returns true if eeprom was written
+static bool
+set_initial_eeprom()
+{
+    uint16_t magic;
+    eeprom_read(magic, magic);
+    if (magic == EXPECT_MAGIC)
+    {
+        return false;
+    }
+
+    ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+    {
+        eeprom_write(measure_wake, measure_wake);
+        eeprom_write(comms_wake, comms_wake);
+        eeprom_write(wake_secs, wake_secs);
+        eeprom_write(fridge_setpoint, fridge_setpoint);
+        eeprom_write(fridge_difference, fridge_difference);
+        eeprom_write(fridge_delay, fridge_delay);
+        eeprom_write(overshoot_delay, overshoot_delay);
+        eeprom_write(overshoot_factor, overshoot_factor);
+        magic = EXPECT_MAGIC;
+        eeprom_write(magic, magic);
+    }
+
+    return true;
+}
+
+static void
+cmd_set_fridge_setpoint(char *params)
+{
+    float new_f = atof(params);
+    if (new_f < 2 || new_f > 30)
+    {
+        printf_P(PSTR("Bad fridge value %f\n"), new_f);
+        return;
+    }
+
+    int16_t old_setpoint = fridge_setpoint;
+
+    fridge_setpoint = new_f * 10;
+    bool written = set_initial_eeprom();
+    if (!written)
+    {
+        if (old_setpoint != fridge_setpoint)
+        {
+            ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+            {
+                eeprom_write(fridge_setpoint, fridge_setpoint);
+            }
+        }
+    }
+    printf_P(PSTR("old fridge %.1fº new fridge %.1fº\n"), 
+            old_setpoint / 10.0f, fridge_setpoint / 10.0f);
+}
+
+static void
+cmd_set_fridge_difference(char *params)
+{
+    float new_f = atof(params);
+    if (new_f < 0 || new_f > 30)
+    {
+        printf_P(PSTR("Bad fridge value %f\n"), new_f);
+        return;
+    }
+
+    fridge_difference = new_f * 10;
+    bool written = set_initial_eeprom();
+    if (!written)
+    {
+        ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+        {
+            eeprom_write(fridge_difference, fridge_difference);
+        }
+    }
+    printf_P(PSTR("new fridge difference %.1fº\n"), fridge_difference / 10.0f);
+}
+
+static void
+cmd_set_fridge_delay(char *params)
+{
+    uint16_t new_delay = atoi(params);
+    if (new_delay < 5)
+    {
+        printf_P(PSTR("Bad fridge delay %d\n"), new_delay);
+        return;
+    }
+
+    fridge_delay = new_delay;
+    bool written = set_initial_eeprom();
+    if (!written)
+    {
+        ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+        {
+            eeprom_write(fridge_delay, fridge_delay);
+        }
+    }
+    printf_P(PSTR("new fridge delay %hu\n"), fridge_delay);
+}
+
+static void
+cmd_set_overshoot_factor(char *params)
+{
+    float new_f = atof(params);
+    if (new_f <= 0 || new_f > 20)
+    {
+        printf_P(PSTR("Bad overshoot factor %f\n"), new_f);
+        return;
+    }
+
+    uint8_t old = overshoot_factor;
+
+    overshoot_factor = new_f * 10;
+    bool written = set_initial_eeprom();
+    if (!written)
+    {
+        if (old != overshoot_factor)
+        {
+            ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+            {
+                eeprom_write(overshoot_factor, overshoot_factor);
+            }
+        }
+    }
+    printf_P(PSTR("old factor %.1fº new factor %.1fº\n"), 
+            old / 10.0f, overshoot_factor / 10.0f);
+}
+    
+static void
+cmd_set_overshoot_delay(char *params)
+{
+    uint16_t new_delay = atoi(params);
+    if (new_delay < 5)
+    {
+        printf_P(PSTR("Bad overshoot delay %d\n"), new_delay);
+        return;
+    }
+
+    overshoot_delay = new_delay;
+    bool written = set_initial_eeprom();
+    if (!written)
+    {
+        ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+        {
+            eeprom_write(overshoot_delay, overshoot_delay);
+        }
+    }
+    printf_P(PSTR("new overshoot delay %hu\n"), overshoot_delay);
+}
+
+static void
+cmd_awake()
+{
+    stay_awake = 1;
+    printf_P(PSTR("awake\n"));
+}
+
+static void
+read_handler()
+{
+    if (strcmp_P(readbuf, PSTR("fetch")) == 0)
+    {
+        cmd_fetch();
+    }
+    else if (strcmp_P(readbuf, PSTR("clear")) == 0)
+    {
+        cmd_clear();
+    }
+    else if (strcmp_P(readbuf, PSTR("btoff")) == 0)
+    {
+        cmd_btoff();
+    }
+    else if (strcmp_P(readbuf, PSTR("measure")) == 0)
+    {
+        cmd_measure();
+    }
+    else if (strcmp_P(readbuf, PSTR("sensors")) == 0)
+    {
+        cmd_sensors();
+    }
+    else if (strcmp_P(readbuf, PSTR("get_params")) == 0)
+    {
+        cmd_get_params();
+    }
+    else if (strncmp_P(readbuf, PSTR("set_params "), 11) == 0)
+    {
+        cmd_set_params(&readbuf[11]);
+    }
+    else if (strcmp_P(readbuf, PSTR("awake")) == 0)
+    {
+        cmd_awake();
+    }
+    else if (strncmp_P(readbuf, PSTR("fridge_setpoint "), 16) == 0)
+    {
+        cmd_set_fridge_setpoint(&readbuf[16]);
+    }
+    else if (strncmp_P(readbuf, PSTR("fridge_diff "), 12) == 0)
+    {
+        cmd_set_fridge_difference(&readbuf[12]);
+    }
+    else if (strncmp_P(readbuf, PSTR("fridge_delay "), 13) == 0)
+    {
+        cmd_set_fridge_delay(&readbuf[13]);
+    }
+    else if (strncmp_P(readbuf, PSTR("overshoot_delay "), 16) == 0)
+    {
+        cmd_set_overshoot_delay(&readbuf[16]);
+    }
+    else if (strncmp_P(readbuf, PSTR("overshoot_factor "), 17) == 0)
+    {
+        cmd_set_overshoot_factor(&readbuf[17]);
+    }
+    else if (strcmp_P(readbuf, PSTR("reset")) == 0)
+    {
+        cmd_reset();
+    }
+    else
+    {
+        printf_P(PSTR("Bad command '%s'\n"), readbuf);
+    }
+}
+
+ISR(INT0_vect)
+{
+    button_pressed = 1;
+    blink();
+    _delay_ms(100);
+    blink();
+}
+
+
+ISR(USART_RX_vect)
+{
+    char c = UDR0;
+#ifdef HAVE_UART_ECHO
+    uart_putchar(c, NULL);
+#endif
+    if (c == '\r' || c == '\n')
+    {
+        if (readpos > 0)
+        {
+            readbuf[readpos] = '\0';
+            have_cmd = 1;
+            readpos = 0;
+        }
+    }
+    else
+    {
+        readbuf[readpos] = c;
+        readpos++;
+        if (readpos >= sizeof(readbuf))
+        {
+            readpos = 0;
+        }
+    }
+}
+
+ISR(TIMER2_COMPA_vect)
+{
+    TCNT2 = 0;
+    measure_count += TICK;
+    comms_count += TICK;
+
+    clock_epoch += TICK;
+
+    if (comms_timeout != 0)
+    {
+        comms_timeout -= TICK;
+    }
+
+    if (measure_count >= measure_wake)
+    {
+        measure_count = 0;
+        need_measurement = 1;
+    }
+
+    if (comms_count >= comms_wake)
+    {
+        comms_count = 0;
+        need_comms = 1;
+    }
+}
+
+static void
+deep_sleep()
+{
+    // p119 of manual
+    OCR2A = SLEEP_COMPARE;
+    loop_until_bit_is_clear(ASSR, OCR2AUB);
+
+    set_sleep_mode(SLEEP_MODE_PWR_SAVE);
+    sleep_mode();
+}
+
+static void
+idle_sleep()
+{
+    set_sleep_mode(SLEEP_MODE_IDLE);
+    sleep_mode();
+}
+
+static uint16_t
+adc_vcc()
+{
+    PRR &= ~_BV(PRADC);
+    
+    // /16 prescaler
+    ADCSRA = _BV(ADEN) | _BV(ADPS2);
+
+    // set to measure 1.1 reference
+    ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
+    // average a number of samples
+    uint16_t sum = 0;
+    uint8_t num = 0;
+    for (uint8_t n = 0; n < 20; n++)
+    {
+        ADCSRA |= _BV(ADSC);
+        loop_until_bit_is_clear(ADCSRA, ADSC);
+
+        uint8_t low_11 = ADCL;
+        uint8_t high_11 = ADCH;
+        uint16_t val = low_11 + (high_11 << 8);
+
+        if (n >= 4)
+        {
+            sum += val;
+            num++;
+        }
+    }
+    ADCSRA = 0;
+    PRR |= _BV(PRADC);
+
+    //float res_volts = 1.1 * 1024 * num / sum;
+    //return 1000 * res_volts;
+    return ((uint32_t)1100*1024*num) / sum;
+}
+
+static void
+do_fridge()
+{
+    struct epoch_ticks now;
+    get_epoch_ticks(&now);
+    uint32_t off_time = now.ticks - fridge_off_clock.ticks;
+    bool wort_valid = last_wort != DS18X20_INVALID_DECICELSIUS;
+    bool fridge_valid = last_fridge != DS18X20_INVALID_DECICELSIUS;
+
+    int16_t wort_max = fridge_setpoint + fridge_difference;
+    int16_t wort_min = fridge_setpoint;
+
+    // the fridge min/max only apply if the wort sensor is broken
+    int16_t fridge_min = fridge_setpoint - FRIDGE_AIR_MIN_RANGE;
+    int16_t fridge_max = fridge_setpoint + FRIDGE_AIR_MAX_RANGE;
+
+    uint8_t fridge_on = PORT_FRIDGE & _BV(PIN_FRIDGE);
+    printf_P(PSTR("last_wort %hd (%hd, %hd), last_fridge %hd (%hd, %hd), setpoint %hd, diff %hd, fridge_on %hhu\n"), 
+            last_wort, wort_min, wort_max, 
+            last_fridge, fridge_min, fridge_max, 
+            fridge_setpoint, fridge_difference, fridge_on);
+
+    if (off_time < fridge_delay)
+    {
+        printf_P(PSTR("waiting for fridge delay current %hu, wait %hu\n"),
+                off_time, fridge_delay);
+        return;
+    }
+
+    // handle failure of the wort sensor. if it is a short (intermittent?)
+    // failure we wait until it has been broken for a period of time
+    // (WORT_INVALID_TIME) before doing anything.
+    if (wort_valid)
+    {
+        wort_valid_clock = now;
+    }
+    else
+    {
+        printf_P(PSTR("wort sensor is invalid\n"));
+        uint32_t invalid_time = now.ticks - wort_valid_clock.ticks;
+        if (invalid_time < WORT_INVALID_TIME)
+        {
+            printf("only been invalid for %ld, waiting\n", invalid_time);
+            return;
+        }
+    }
+
+    if (!fridge_valid)
+    {
+        printf_P(PSTR("fridge sensor is invalid\n"));
+    }
+
+    if (fridge_on)
+    {
+        bool turn_off = false;
+        uint16_t on_time = now.ticks - fridge_on_clock.ticks;
+
+        uint16_t overshoot = 0;
+        if (on_time > overshoot_delay)
+        {
+            overshoot = overshoot_factor * MIN(OVERSHOOT_MAX_DIV, on_time) / OVERSHOOT_MAX_DIV;
+        }
+
+        printf_P(PSTR("on_time %hu, overshoot %hu\n"), on_time, overshoot);
+
+        // wort has cooled enough. will probably cool a bit more by itself
+        if (wort_valid)
+        {
+            if ((last_wort - overshoot) < fridge_setpoint)
+            {
+                printf_P(PSTR("wort has cooled enough, overshoot %hu on_time %hu\n"), overshoot, on_time);
+                turn_off = true;
+            }
+        }
+        else
+        {
+            if (fridge_valid && last_fridge < fridge_min)
+            {
+                printf_P(PSTR("fridge off fallback\n"));
+                turn_off = true;
+            }
+        }
+
+        if (turn_off)
+        {
+            // too cold, turn off
+            printf_P(PSTR("Turning fridge off\n"));
+            PORT_FRIDGE &= ~_BV(PIN_FRIDGE);
+            fridge_off_clock = now;
+        }
+    }
+    else
+    {
+        bool turn_on = false;
+
+        if (wort_valid)
+        {
+            if (last_wort >= wort_max)
+            {
+                printf_P(PSTR("wort is too hot\n"));
+                turn_on = true;
+            }
+        }
+        else
+        {
+            if (fridge_valid && last_fridge >= fridge_max)
+            {
+                printf_P(PSTR("fridge on fallback\n"));
+                turn_on = true;
+            }
+        }
+
+        if (turn_on)
+        {
+            // too hot, turn on
+            printf_P(PSTR("Turning fridge on\n"));
+            PORT_FRIDGE |= _BV(PIN_FRIDGE);
+            fridge_on_clock = now;
+        }
+    }
+}
+
+static void
+do_measurement()
+{
+    blink();
+
+    /* Take the timer here since deep_sleep() below could take 6 seconds */
+    get_epoch_ticks(&last_measurement_clock);
+    if (n_measurements == 0)
+    {
+        first_measurement_clock = last_measurement_clock;
+    }
+
+    simple_ds18b20_start_meas(NULL);
+    _delay_ms(DS18B20_TCONV_12BIT);
+
+    if (n_measurements == max_measurements)
+    {
+        n_measurements = 0;
+    }
+
+    for (uint8_t s = 0; s < n_sensors; s++)
+    {
+        uint16_t reading;
+        uint8_t ret = simple_ds18b20_read_raw(sensor_id[s], &reading);
+        if (ret != DS18X20_OK)
+        {
+            reading = VALUE_BROKEN;
+        }
+        set_measurement(s, n_measurements, reading);
+
+        if (memcmp(sensor_id[s], fridge_id, sizeof(fridge_id)) == 0)
+        {
+            last_fridge = ds18b20_raw16_to_decicelsius(reading);
+        }
+        if (memcmp(sensor_id[s], wort_id, sizeof(wort_id)) == 0)
+        {
+            last_wort = ds18b20_raw16_to_decicelsius(reading);
+        }
+    }
+
+    n_measurements++;
+}
+
+static void
+do_comms()
+{
+    get_epoch_ticks(&last_comms_clock);
+
+    // turn on bluetooth
+    set_aux_power(1);
+    // avoid receiving rubbish, perhaps
+    _delay_ms(50);
+    uart_on();
+    
+    // write sd card here? same 3.3v regulator...
+    
+    for (comms_timeout = wake_secs; 
+        comms_timeout > 0 || stay_awake;  
+        )
+    {
+        if (need_measurement)
+        {
+            need_measurement = 0;
+            do_measurement();
+            do_fridge();
+            continue;
+        }
+
+        if (have_cmd)
+        {
+            have_cmd = 0;
+            read_handler();
+            continue;
+        }
+
+        // wait for commands from the master
+        idle_sleep();
+    }
+
+    uart_off();
+    // in case bluetooth takes time to flush
+    _delay_ms(100);
+    set_aux_power(0);
+}
+
+static void
+blink()
+{
+    PORT_LED &= ~_BV(PIN_LED);
+    _delay_ms(1);
+    PORT_LED |= _BV(PIN_LED);
+}
+
+static void
+long_delay(int ms)
+{
+    int iter = ms / 100;
+
+    for (int i = 0; i < iter; i++)
+    {
+        _delay_ms(100);
+    }
+}
+
+ISR(BADISR_vect)
+{
+    //uart_on();
+    printf_P(PSTR("Bad interrupt\n"));
+}
+
+int main(void)
+{
+    setup_chip();
+    blink();
+
+    set_aux_power(0);
+
+    stdout = &mystdout;
+    uart_on();
+
+    printf(PSTR("Started.\n"));
+
+    load_params();
+
+    init_sensors();
+
+    uart_off();
+
+    // turn off everything except timer2
+    PRR = _BV(PRTWI) | _BV(PRTIM0) | _BV(PRTIM1) | _BV(PRSPI) | _BV(PRUSART0) | _BV(PRADC);
+
+    setup_tick_counter();
+
+    sei();
+
+    need_comms = 1;
+    need_measurement = 1;
+
+    stay_awake = 1;
+
+    for(;;)
+    {
+        if (button_pressed)
+        {
+            // debounce
+            _delay_ms(200);
+            need_comms = 1;
+            comms_timeout = wake_secs;
+            button_pressed = 0;
+            continue;
+        }
+
+        if (need_comms)
+        {
+            need_comms = 0;
+            do_comms();
+            continue;
+        }
+
+        if (need_measurement)
+        {
+            need_measurement = 0;
+            do_measurement();
+            do_fridge();
+            continue;
+        }
+
+        deep_sleep();
+    }
+
+    return 0;   /* never reached */
+}