diff --git a/Makefile b/Makefile
index 8e16276..408a122 100644
--- a/Makefile
+++ b/Makefile
@@ -8,10 +8,15 @@ flash: build
 
 build: gympal.hex
 
-gympal.hex: src/gympal.c bin
-	avr-gcc -Wall -Os -DF_CPU=16000000UL -mmcu=atmega328p -c src/gympal.c -o bin/gympal.o
-	avr-gcc -Os -mmcu=atmega328p -o bin/gympal.elf bin/gympal.o
+gympal.hex: gympal.o control.o
+	avr-gcc -Os -mmcu=atmega328p -o bin/gympal.elf bin/gympal.o bin/control.o
 	avr-objcopy -O ihex -R .eeprom bin/gympal.elf bin/gympal.hex
 
+gympal.o: src/gympal.c bin
+	avr-gcc -Wall -Os -DF_CPU=16000000UL -mmcu=atmega328p -c -o bin/gympal.o src/gympal.c
+
+control.o: src/control.c bin
+	avr-gcc -Wall -Os -DF_CPU=16000000UL -mmcu=atmega328p -c -o bin/control.o src/control.c
+
 bin:
 	mkdir bin
\ No newline at end of file
diff --git a/src/control.c b/src/control.c
new file mode 100644
index 0000000..0a829fd
--- /dev/null
+++ b/src/control.c
@@ -0,0 +1,47 @@
+#include "control.h"
+
+volatile uint8_t CTL_INPUT_FLAGS = 0;
+
+uint8_t readPin(uint8_t inputRegister, uint8_t inputPin) {
+    return (inputRegister & (1 << inputPin)) >> inputPin;
+}
+
+ISR(PCINT2_vect) {
+    cli();
+    uint8_t rotDt = readPin(PIND, CTL_ROTARY_ENCODER_DT_IN);
+    uint8_t rotClk = readPin(PIND, CTL_ROTARY_ENCODER_CLK_IN);
+    uint8_t buttonA = readPin(PIND, CTL_BUTTON_A_IN);
+    uint8_t buttonB = readPin(PIND, CTL_BUTTON_B_IN);
+    uint8_t buttonC = readPin(PIND, CTL_BUTTON_C_IN);
+    CTL_INPUT_FLAGS = (
+        (rotDt << CTL_ROTARY_ENCODER_DT_FLAG) |
+        (rotClk << CTL_ROTARY_ENCODER_CLK_FLAG) |
+        (buttonA << CTL_BUTTON_A_FLAG) |
+        (buttonB << CTL_BUTTON_B_FLAG) |
+        (buttonC << CTL_BUTTON_C_FLAG)
+    );
+    sei();
+}
+
+void ctl_init() {
+    // Set all control pins as input (0).
+    DDRD &= ~(
+        (1 << CTL_ROTARY_ENCODER_DT) |
+        (1 << CTL_ROTARY_ENCODER_CLK) |
+        (1 << CTL_BUTTON_A) |
+        (1 << CTL_BUTTON_B) |
+        (1 << CTL_BUTTON_C)
+    );
+    // Set up interrupts for handling control pin state changes.
+    // Luckily, all interrupts happen on PCINT[16..23] so we only need one interrupt to handle them all.
+    PCICR |= 1 << PCIE2; // Enable PCINT2_vector interrupts.
+    PCMSK2 |= (// Enable the flag for each input we want to cause interrupts on state change.
+        (1 << CTL_ROTARY_ENCODER_DT_INT) |
+        (1 << CTL_ROTARY_ENCODER_CLK_INT) |
+        (1 << CTL_BUTTON_A_INT) |
+        (1 << CTL_BUTTON_B_INT) |
+        (1 << CTL_BUTTON_C_INT)
+    );
+    // Enable the global interrupt flag.
+    sei();
+}
\ No newline at end of file
diff --git a/src/control.h b/src/control.h
new file mode 100644
index 0000000..d88db2d
--- /dev/null
+++ b/src/control.h
@@ -0,0 +1,39 @@
+#ifndef CONTROL_H
+#define CONTROL_H
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+#define CTL_ROTARY_ENCODER_DT PORTD2
+#define CTL_ROTARY_ENCODER_DT_IN PIND2
+#define CTL_ROTARY_ENCODER_DT_INT PCINT18
+#define CTL_ROTARY_ENCODER_DT_FLAG 0
+
+#define CTL_ROTARY_ENCODER_CLK PORTD3
+#define CTL_ROTARY_ENCODER_CLK_IN PIND3
+#define CTL_ROTARY_ENCODER_CLK_INT PCINT19
+#define CTL_ROTARY_ENCODER_CLK_FLAG 1
+
+#define CTL_BUTTON_A PORTD5
+#define CTL_BUTTON_A_IN PIND5
+#define CTL_BUTTON_A_INT PCINT21
+#define CTL_BUTTON_A_FLAG 2
+
+#define CTL_BUTTON_B PORTD6
+#define CTL_BUTTON_B_IN PIND6
+#define CTL_BUTTON_B_INT PCINT22
+#define CTL_BUTTON_B_FLAG 3
+
+#define CTL_BUTTON_C PORTD7
+#define CTL_BUTTON_C_IN PIND7
+#define CTL_BUTTON_C_INT PCINT23
+#define CTL_BUTTON_C_FLAG 4
+
+extern volatile uint8_t CTL_INPUT_FLAGS;
+
+/**
+ * @brief Initializes the user control inputs and interrupts.
+ */
+void ctl_init();
+
+#endif
\ No newline at end of file
diff --git a/src/gympal.c b/src/gympal.c
index 634dba8..dd25570 100644
--- a/src/gympal.c
+++ b/src/gympal.c
@@ -1,33 +1,24 @@
 #include <avr/io.h>
-#include <avr/interrupt.h>
 #include <util/delay.h>
 
-volatile uint8_t a = 0;
-
-void updatePin12(uint8_t status) {
-    PORTB = status << PORTB4;
-}
-
-ISR(PCINT2_vect) {
-    uint8_t value = (PIND & (1 << PIND5)) >> PIND5;
-    PORTB = value << PORTB4;
-}
+#include "control.h"
 
 int main() {
-    PCICR |= 1 << PCIE2;
-    PCMSK2 |= 1 << PCINT21;
-    sei();
-    // Pin 12 == Port B4, aka 4th bit on the B register.
-    // Set pin 12 as output.
+    ctl_init();
+    // Just for testing the interrupts, we're setting up B4 as an indicator LED.
     DDRB |= 1 << PORTB4;
-    // Set pin 5 as input.
-    DDRD &= ~(1 << PORTD5);
     PORTB &= ~(1 << PORTB4);
-    while (1) {
-        // updatePin12(ledOn);
-        // ledOn = !ledOn;
-        // _delay_ms(1000.0);
-        // DO NOTHING! rely on interrupt.
+    uint8_t led = 0;
+    while(1) {
+        uint8_t v = (CTL_INPUT_FLAGS & (1 << CTL_BUTTON_B_FLAG)) >> CTL_BUTTON_A_FLAG;
+        if (led != v) {
+            led = v;
+            if (led) {
+                PORTB |= 1 << PORTB4;
+            } else {
+                PORTB &= ~(1 << PORTB4);
+            }
+        }
     }
     return 0;
 }
\ No newline at end of file