// Init OLED over SPI

    ssd1306_Init();

    ssd1306_clearscreen();

    // Check for problems on startup

    if(clock_fail) {

        //ssd1306_DrawStringBig("ERROR: Check Xtal", 2, 0);

        ssd1306_DrawStringBig("NO XTAL", 2, 0);

        delay(1000);

        ssd1306_clearscreen();

    }

    // Init USB

    //Set_System(); // hw_config.h

    Set_USBClock();

    USB_Interrupts_Config();

    USB_Init();

    //SYSCFG_USBPuCmd(ENABLE);

    //PowerOn();

    // Startup screen 

    ssd1306_DrawString("therm v0.1", 1, 40);

    ssd1306_DrawString("protofusion.org/therm", 3, 0);

    delay(1500);

    ssd1306_clearscreen();

    restore_settings();

    if(boottobrew)

      state = STATE_PREHEAT_BREW; // Go to brew instead of idle if configured thusly

    GPIO_ResetBits(LED_STAT);

    // Main loop

    while(1)

    {

        // Process sensor inputs

        process();

        // Run state machine

        machine(); 

    }

}

// Read temperature and update global temp vars

int32_t temp = 0;

uint8_t temp_frac = 0;

void update_temp() {

    // Assert CS

    GPIO_ResetBits(MAX_CS);

    delay(1);

    // This may not clock at all... might need to send 16 bits first

    SPI_I2S_SendData(SPI2, 0xAAAA); // send dummy data

    //SPI_I2S_SendData(SPI2, 0xAA); // send dummy data

    uint16_t temp_pre = SPI_I2S_ReceiveData(SPI2);

    if(temp_pre & 0b0000000000000010) {

        ssd1306_DrawString("Fatal Error", 3, 35);

        state = STATE_TC_ERROR;

    }

    else if(temp_pre & 0b0000000000000001 && !ignore_tc_error) {

        state = STATE_TC_ERROR;

        temp = 0;

        temp_frac = 0;

    }

    else 

    {

        if(state == STATE_TC_ERROR)

        uint8_t sign = temp >> 15;// top bit is sign

        temp_pre = temp_pre >> 2; // Drop 2 lowest bits

        temp_frac = temp_pre & 0b11; // get fractional part

        temp_frac *= 25; // each bit is .25 a degree, up to fixed point

        temp_pre = temp_pre >> 2; // Drop 2 fractional bits 

        if(sign) {

            temp = -temp_pre;

        }

        else {

            temp = temp_pre;

        }

        if(temp_units == TEMP_UNITS_FAHRENHEIT) {

            temp *= 9; // fixed point mul by 1.8

            temp /= 5;

            temp += 32;

            temp_frac *= 9;

            temp_frac /= 5;

            temp_frac += 32;

            temp += temp_frac/100; // add overflow to above

            temp_frac %= 100;

        }

    }

    // Deassert CS

    delay(1);

    GPIO_SetBits(MAX_CS);

}

// PID implementation

// TODO: Make struct that has the last_temp and i_state in it, pass by ref. Make struct that has other input values maybe.

int16_t last_pid_temp = 0;

uint8_t last_pid_temp_frac = 0;

int16_t i_state = 0;

int16_t update_pid(uint16_t k_p, uint16_t k_i, uint16_t k_d, int16_t temp, uint8_t temp_frac, int16_t setpoint) 

{

  // Calculate instantaneous error

  int16_t error = (int16_t)setpoint - (int16_t)temp; // TODO: Use fixed point fraction

  // Proportional component

  int16_t p_term = k_p * error;