A simple Integral fan controller driving three PC fans.

FanController.c

#include "msp430G2452.h"

#define	FAN_CNT		(3)
#define PWM_FREQ	(32)
#define PWM_RESS	(128)

// Port 1
#define	LED1	(1<<0)
#define	TMP_RX	(1<<1)
static const int TACH[]	= { (1<<3), (1<<4), (1<<5) };
// Port 2
static const int FAN[] = { (1<<0), (1<<1), (1<<2) };

#define LED1_ON()	(P1OUT &= ~LED1)
#define LED1_OFF()	(P1OUT |= LED1)

volatile struct {
	int second;
	int fracofsec;
	unsigned int rpmdata[2][FAN_CNT];
	unsigned int maxrpm[FAN_CNT];
	unsigned int fanpwr[FAN_CNT];
	unsigned int fanrpm[FAN_CNT];
} fs;

void tempCTLAlg(void);
int bound(int low, int mid, int high);
int takeADCReading(int channel);

void main(void) {
	// Kill Boris - we don't need a watchdog
	WDTCTL = WDTPW + WDTHOLD;
	
	// Clock system
	DCOCTL = CALDCO_16MHZ;
	BCSCTL1 = CALBC1_16MHZ;
	BCSCTL2 = SELS; // DCO slave clock

	// Timer A
	TA0CTL = TASSEL_2 | MC_1; // SCLK, UP
	TA0CCR0 = (32768 / PWM_FREQ / PWM_RESS) - 1;
	TA0CCTL0 = CCIE;

	// ADC10
	ADC10CTL0 = SREF_0 | ADC10ON; // Vcc reference
	ADC10CTL1 = INCH0 | ADC10SSEL1; // Channel A1, MCLK
	ADC10AE0 = (1<<1);

	// IO Port 1
	P1DIR = LED1;
	P1IE = TMP_RX | TACH[0] | TACH[1] | TACH[2]; // Enable ints
	P1IES = 0xFF; // H-L transition int
	P1IFG = 0x00; // Clear noise interrupts

	// IO Port 2
	P2DIR = FAN[0] | FAN[1] | FAN[2];

	// Start interrupts
	_BIS_SR(GIE);
	int i;


	// Three second startup at full power
	for (i=0; i<FAN_CNT; i++)
		fs.fanpwr[i] = PWM_RESS;
	while (fs.second <3) ;
	for (i=0; i<FAN_CNT; i++) {
		fs.maxrpm[i] = fs.rpmdata[1][i];
		fs.fanrpm[i] = 2 * fs.maxrpm[i] / 3;
	}
	fs.fanrpm[0] = fs.fanrpm[0] / 2;


	while (1) {
		if (fs.second) {
			fs.second--;
			tempCTLAlg();
		}
	}
}

// Temperature Control Algorithm
// Do the 1Hz work to try and keep the temperature on target
void tempCTLAlg(void) {
	int tempsense = takeADCReading(1);
	int lightvote = 0;
	int i;

	int tempDelta = tempsense - 280;

	for (i=0; i<FAN_CNT; i++) {
		fs.fanrpm[i] = bound(fs.maxrpm[i]>>2, fs.fanrpm[i] + tempDelta, fs.maxrpm[i]);
		int rpmDelta = fs.rpmdata[1][i] - fs.fanrpm[i];
		fs.fanpwr[i] = bound(0, fs.fanpwr[i] - (rpmDelta/250), PWM_RESS);

		if (rpmDelta < 0) { // too slow
			lightvote++;
		} else {// too fast
			lightvote--;
		}

	}

	if (tempDelta > 0) {
		LED1_ON();
	} else {
		LED1_OFF();
	}
}

int bound(int low, int mid, int high) {
	if (low > mid)
		mid = low;
	if (high < mid)
		mid = high;
	return mid;
}

int takeADCReading(int channel) {
	ADC10CTL1 = (ADC10CTL1 & 0x0FFF) | (channel << 12);
	ADC10CTL0 |= ENC | ADC10SC;

	while (ADC10CTL1 & ADC10BUSY) ;

	return ADC10MEM;
}

#pragma vector=TIMER0_A0_VECTOR
__interrupt void Timer_A00 (void) {
	int i, fracofpwm;
	fs.fracofsec = (fs.fracofsec + 1) % (PWM_FREQ * PWM_RESS);
	if (fs.fracofsec == 0) {
		for (i=0; i<FAN_CNT; i++) {
			fs.rpmdata[1][i] = 30 * fs.rpmdata[0][i];
			fs.rpmdata[0][i] = 0;
		}
		fs.second++;
	}
	fracofpwm = fs.fracofsec%PWM_RESS;
	if (fracofpwm == 0) {
		// Turn on enabled fans
		P2OUT |= FAN[0] | FAN[1] | FAN[2];
	}
	for (i=0; i<FAN_CNT; i++) {
		if (fs.fanpwr[i] < fracofpwm) {
			P2OUT &= ~(FAN[i]);
		}
	}
}

#pragma vector=PORT1_VECTOR
__interrupt void Port1 (void) {
	unsigned int pins = P1IFG;
	P1IFG = 0x00;

	unsigned int i;
	for (i=0; i<FAN_CNT; i++) {
		if (pins & TACH[i]) {
			fs.rpmdata[0][i]++;
		}
	}
}