diff --git a/Makefile b/Makefile
index dfbbf07..be32f54 100644
--- a/Makefile
+++ b/Makefile
@@ -45,7 +45,7 @@ CFLAGS+=-Ifxplib/include -DPOINTPOS=16
 LDFLAGS+=-Lfxplib/lib/$(BUILD) -lfxp_stm32l0
 
 # generic linking
-LDFLAGS+=-Wl,--start-group -lc -lgcc -lnosys -Wl,--end-group
+LDFLAGS+=-Wl,--start-group -lc -lm -lgcc -lnosys -Wl,--end-group
 
 # build type specific flags
 CFLAGS_debug=-O0 -ggdb -DDEBUG
diff --git a/src/main.c b/src/main.c
index ebe55d9..4915387 100644
--- a/src/main.c
+++ b/src/main.c
@@ -17,10 +17,11 @@ static void clock_setup(void)
 {
 	/* We are running on MSI (2.1 MHz) after boot. */
 	rcc_periph_clock_enable(RCC_GPIOA); // for basically everything
-	rcc_periph_clock_enable(RCC_GPIOC); // for UART only
 
-	/* Enable clocks for USART2. */
+	/* Enable clocks for peripherals. */
 	rcc_periph_clock_enable(RCC_USART2);
+	rcc_periph_clock_enable(RCC_ADC1);
+	rcc_periph_clock_enable(RCC_TIM21);
 }
 
 /* Set up systick to fire freq times per second */
@@ -59,7 +60,8 @@ int main(void)
 
 	fan_ctrl_pwm_enable(); // TODO: make DC/PWM configurable
 
-	// triggered every 1 ms
+	uint8_t last_duty = 0;
+
 	while (1) {
 		if(systick_triggered) {
 			systick_triggered = false;
@@ -77,7 +79,17 @@ int main(void)
 
 			uint8_t duty = fan_controller_update(temperature);
 
+			// handle fan power-on and power-off
+			if(last_duty == 0 && duty != 0) {
+				fan_ctrl_pwm_enable();
+			} else if(last_duty != 0 && duty == 0) {
+				fan_ctrl_pwm_disable();
+			}
+
+			// set the updated duty cycle
 			fan_ctrl_pwm_set_duty(duty);
+
+			last_duty = duty;
 		}
 
 		__WFI();