/**
 * Fan controller.
 * AN0 - Potentiometer input (0-5V).
 * PWM1 - Motor speed control output.
 * T1G - Motor tachometer signal input (4-42Hz pulses).
 * PWM3 - Tachometer panel meter output.
 */

#include "mcc_generated_files/mcc.h"

// This is 100% for the motor PWM output (PWM1PRH, PWM1PRL).
#define FAN_DUTY_MAX (255)
// Should be set higher than the minimum starting speed.
#define FAN_DUTY_MIN (38)

// Full-scale deflection on the tachometer.
#define TACH_HZ_MAX (50)
// 100% duty cycle for the tachometer PWM output (PWM3PRH, PWM3PRL).
#define TACH_DUTY_MAX (255)
// Timer1 is set to use LFINTOSC, so this is simply that clock speed (31kHz).
#define TMR1_COUNTS_PER_SECOND (31000)

/**
 * Set PWM to control motor speed from potentiometer position.
 */
void setSpeedFromPot()
{
    adc_result_t potPosition;
    uint16_t pwmDutyCycle;
    
    ADC1_StartConversion();
    potPosition = ADC1_GetConversionResult();
    pwmDutyCycle = (potPosition >> 2) + FAN_DUTY_MIN;

    if (pwmDutyCycle > FAN_DUTY_MAX)
    {
        pwmDutyCycle = FAN_DUTY_MAX;
    }

    PWM1_DutyCycleSet(pwmDutyCycle);
    PWM1_LoadBufferSet();
}

// The moving coil meter doesn't respond linearly with input voltage.
// Apply the inverse of that response to the PWM output so it appears linear.
uint16_t applyMeterCorrection(uint32_t x)
{
    uint16_t x3 = (x * x * x) / 71430;
    uint16_t x2 = (x * x) / 278;
    return (x3 - x2) + x;
}

/**
 * The tachometer output from the motor is one pulse per revolution.
 * Since its duty cycle is 50%, the RPM can be determined from the width of a single pulse.
 * Use that to set a PWM output that is sent to a panel meter.
 */
void setTachFromTach()
{
    uint16_t pulseWidthCounts;
    uint32_t pwmDutyCycle;
    
    if (TMR0_HasOverflowOccured())
    {
        // TMR0 sets an upper limit on how long to wait for a pulse. If one hasn't occurred by then, the speed is probably 0.
        PWM3_DutyCycleSet(0);
        PWM3_LoadBufferSet();
        
        TMR0_Reload();
        INTCONbits.TMR0IF = 0;
    }
    else if (TMR1_HasOverflowOccured())
    {
        // The fan shouldn't normally be able to spin this slow, but just in case, treat it as 0.
        PWM3_DutyCycleSet(0);
        PWM3_LoadBufferSet();
        
        TMR1_StopTimer();
        T1GCONbits.T1GGO = 0;
        PIR1bits.TMR1IF = 0;
        TMR1_Reload();
        TMR1_StartTimer();
        TMR1_StartSinglePulseAcquisition();
        
        TMR0_Reload();
        INTCONbits.TMR0IF = 0;
    }
    else if(T1GCONbits.T1GGO == 0)
    {
        pulseWidthCounts = TMR1_ReadTimer();
        
        pwmDutyCycle = TMR1_COUNTS_PER_SECOND;
        pwmDutyCycle *= TACH_DUTY_MAX;
        pwmDutyCycle /= TACH_HZ_MAX;
        pwmDutyCycle /= 2; // Divide by 2 because the pulse width is only half a cycle.
        pwmDutyCycle /= pulseWidthCounts;

        PWM3_DutyCycleSet(applyMeterCorrection(pwmDutyCycle));
        PWM3_LoadBufferSet();
        
        TMR1_Reload();
        TMR1_StartTimer();
        TMR1_StartSinglePulseAcquisition();
        
        TMR0_Reload();
        INTCONbits.TMR0IF = 0;
    }
}

void main(void)
{
    SYSTEM_Initialize();

    PWM1_Start();
    PWM3_Start();
    TMR1_StartTimer();
    TMR1_StartSinglePulseAcquisition();

    while (1)
    {
        setSpeedFromPot();
        setTachFromTach();
    }
}