diff --git a/src/bus/i2c.c b/src/bus/i2c.c
index a04a244..3de6a19 100644
--- a/src/bus/i2c.c
+++ b/src/bus/i2c.c
@@ -12,8 +12,8 @@
 #define TW_MR_SLA_NACK  0x48
 #define TW_MR_DATA_ACK  0x50
 
-// XXX: Error handling and recovery without watchdog timer.
-// XXX: Implement I2C_vect ISR? This may not actually be
+// TODO: Error handling and recovery without watchdog timer.
+// TODO: Implement I2C_vect ISR? This may not actually be
 // much better than the blocking approach.
 
 static void I2C_AHT20_Reset(void);
@@ -21,8 +21,8 @@ static bool I2C_AHT20_IsCalibrated(void);
 static void I2C_AHT20_Calibrate(void);
 static void I2C_AHT20_Trigger(void);
 
-static int I2C_ADS1115_WriteRegister(unsigned char reg, unsigned short data);
-static unsigned short I2C_ADS1115_ReadRegister(unsigned char reg);
+static int  I2C_ADS1115_WriteRegister(byte reg, word data);
+static word I2C_ADS1115_ReadRegister(byte reg);
 
 int I2C_Init(void)
 {
@@ -34,7 +34,7 @@ int I2C_Init(void)
 	return 0;
 }
 
-int I2C_Start(unsigned char addr, unsigned char mode)
+int I2C_Start(byte addr, byte mode)
 {
 	unsigned int status;
 
@@ -69,7 +69,7 @@ int I2C_Start(unsigned char addr, unsigned char mode)
 	return 0;
 }
 
-int I2C_Write(unsigned char data)
+int I2C_Write(byte data)
 {
 	TWDR = data;
 	TWCR = (1 << TWEN)    // Enable TWI
@@ -83,7 +83,7 @@ int I2C_Write(unsigned char data)
 	return 0;
 }
 
-unsigned char I2C_Read_ACK(void)
+byte I2C_Read_ACK(void)
 {
 	// Read data and acknowledge
 
@@ -98,7 +98,7 @@ unsigned char I2C_Read_ACK(void)
 	return TWDR;
 }
 
-unsigned char I2C_Read_NACK(void)
+byte I2C_Read_NACK(void)
 {
 	// Read data, expect last byte
 
@@ -143,8 +143,8 @@ int I2C_Stop(void)
 
 void I2C_Reset(void)
 {
-	unsigned char TWBRold = TWBR;
-	unsigned char TWARold = TWAR;
+	byte TWBRold = TWBR;
+	byte TWARold = TWAR;
 
 	// TODO: Handle timeouts and reset TWI if necessary,
 	// fatal error after multiple attempts and then bring
@@ -159,7 +159,7 @@ void I2C_Reset(void)
 
 int I2C_SetChannel(int channel)
 {
-	unsigned char crb;
+	byte crb;
 
 	// Excerpts taken from the PCA9546A datasheet:
 	// https://www.ti.com/lit/ds/symlink/pca9546a.pdf
@@ -226,7 +226,7 @@ int I2C_AHT20_Init(void)
 
 int I2C_AHT20_Read(float *temp, float *rhum)
 {
-	unsigned char data[6], crc;
+	byte data[6], crc;
 	unsigned long hraw, traw;
 
 	I2C_AHT20_Trigger();
@@ -289,7 +289,7 @@ static void I2C_AHT20_Reset(void)
 
 static bool I2C_AHT20_IsCalibrated(void)
 {
-	unsigned char status;
+	byte status;
 
 	// Before reading the temperature and humidity
 	// values, first check whether the calibration
@@ -337,7 +337,7 @@ static void I2C_AHT20_Calibrate(void)
 
 static void I2C_AHT20_Trigger(void)
 {
-	unsigned char status;
+	byte status;
 
 	// Send the 0xAC command directly (trigger
 	// measurement). The parameter of this command has
@@ -371,7 +371,7 @@ static void I2C_AHT20_Trigger(void)
 	I2C_Stop();
 }
 
-static int I2C_ADS1115_WriteRegister(unsigned char reg, unsigned short data)
+static int I2C_ADS1115_WriteRegister(byte reg, word data)
 {
 	// The ADS111x have one address pin, ADDR, that
 	// configures the I2C address of the device. This
@@ -415,9 +415,9 @@ static int I2C_ADS1115_WriteRegister(unsigned char reg, unsigned short data)
 	return 0;
 }
 
-static unsigned short I2C_ADS1115_ReadRegister(unsigned char reg)
+static word I2C_ADS1115_ReadRegister(byte reg)
 {
-	unsigned char data[2];
+	byte data[2];
 
 	// To access a specific register from the ADS1115,
 	// the master must first write an appropriate value
@@ -456,10 +456,10 @@ static unsigned short I2C_ADS1115_ReadRegister(unsigned char reg)
 	return data[0] << 8 | data[1];
 }
 
-unsigned short I2C_ADS1115_Read(int channel)
+word I2C_ADS1115_Read(int channel)
 {
-	unsigned short config;
-	unsigned short rate, gain, mux, os;
+	word config;
+	word rate, gain, mux, os;
 
 	// Operational status or single-shot conversion
 	// start: This bit determines the operational
diff --git a/src/bus/i2c.h b/src/bus/i2c.h
index 138ece8..ce004c1 100644
--- a/src/bus/i2c.h
+++ b/src/bus/i2c.h
@@ -1,23 +1,27 @@
 #ifndef MAD_CORE_BUS_I2C_H
 #define MAD_CORE_BUS_I2C_H
 
-// Sensors
-#define AHT01 0x0  // Upper Sensor TWI Channel
-#define AHT02 0x1  // Middle Sensor TWI Channel
-#define AHT03 0x2  // Lower Sensor TWI Channel
+#include "common/types.h"
 
-int I2C_Init(void);
-int I2C_Start(unsigned char addr, unsigned char mode);
-int I2C_SetChannel(int channel);
-int I2C_Write(unsigned char data);
-unsigned char I2C_Read_ACK(void);
-unsigned char I2C_Read_NACK(void);
-int I2C_Wait_ACK(void);
-int I2C_Stop(void);
+// I2C multiplexer channels
+#define AHT01 0x0  // Upper
+#define AHT02 0x1  // Middle
+#define AHT03 0x2  // Lower
 
-int I2C_AHT20_Init(void);
-int I2C_AHT20_Read(float *temp, float *rhum);
+int   I2C_Init(void);
+int   I2C_Start(byte addr, byte mode);
+int   I2C_SetChannel(int channel);
+int   I2C_Write(byte data);
+byte  I2C_Read_ACK(void);
+byte  I2C_Read_NACK(void);
+int   I2C_Wait_ACK(void);
+int   I2C_Stop(void);
 
-unsigned short I2C_ADS1115_Read(int channel);
+// AHT20 temperature and humidity sensor
+int  I2C_AHT20_Init(void);
+int  I2C_AHT20_Read(float *temp, float *rhum);
+
+// ADS1115 analog to digital converter
+word  I2C_ADS1115_Read(int channel);
 
 #endif // MAD_CORE_BUS_I2C_H
diff --git a/src/bus/mosfet.c b/src/bus/mosfet.c
index 260acfd..a0d619e 100644
--- a/src/bus/mosfet.c
+++ b/src/bus/mosfet.c
@@ -7,16 +7,16 @@
 int MOS_Init(void)
 {
 	// PB0: MOSFET #1 Peltier
-	DDRB |= BIT(PB0); // Output
-	PORTB &= ~BIT(PB0); // Low
+	DDRB |= BIT(PB0);    // Output
+	PORTB &= ~BIT(PB0);  // Low
 
 	// PB1: MOSFET #2 Heating
-	DDRB |= BIT(PB1); // Output
-	PORTB &= ~BIT(PB1); // Low
+	DDRB |= BIT(PB1);    // Output
+	PORTB &= ~BIT(PB1);  // Low
 
 	// PB2: MOSFET #3 Lights
-	DDRB |= BIT(PB2); // Output
-	PORTB &= ~BIT(PB2); // Low
+	DDRB |= BIT(PB2);    // Output
+	PORTB &= ~BIT(PB2);  // Low
 
 	return 0;
 }
diff --git a/src/bus/mosfet.h b/src/bus/mosfet.h
index a977149..c003695 100644
--- a/src/bus/mosfet.h
+++ b/src/bus/mosfet.h
@@ -1,15 +1,15 @@
-#ifndef MAD_BUS_MOSFET_H
-#define MAD_BUS_MOSFET_H
+#ifndef MAD_CORE_BUS_MOSFET_H
+#define MAD_CORE_BUS_MOSFET_H
 
 #include <avr/io.h>
 
-// MOSFETS
+// Devices
 #define MOS01 PB0  // Peltier Enable
 #define MOS02 PB1  // Heating Enable
 #define MOS03 PB2  // Lights Enable
 
-int MOS_Init(void);
-void MOS_Enable(int port);
-void MOS_Disable(int port);
+int   MOS_Init(void);
+void  MOS_Enable(int port);
+void  MOS_Disable(int port);
 
-#endif // MAD_BUS_MOSFET_H
+#endif // MAD_CORE_BUS_MOSFET_H
diff --git a/src/bus/pwm.c b/src/bus/pwm.c
index 97773fd..21db7c4 100644
--- a/src/bus/pwm.c
+++ b/src/bus/pwm.c
@@ -9,7 +9,8 @@ int PWM_Init(void)
 
 	DDRD |= BIT(PD4) | BIT(PD5); // | BIT(PD7);
 
-	// Timer1: Fast mode, non-inverting, top=ICR1, prescale /1
+	// TIMER1: Fast mode, non-inverting, top=ICR1, prescale /1
+
 	TCCR1A = BIT(WGM11) | BIT(COM1A1) | BIT(COM1B1);
 	TCCR1B = BIT(WGM12) | BIT(WGM13) | BIT(CS10);
 	ICR1 = PWM_CYCLE_TOP; // 8000 MHz / 25000 KHz
@@ -26,7 +27,8 @@ int PWM_Init(void)
 	// 8-bit this gives us a really low duty step size of 2.5%.
 	// Ideal would be two 16-bit timers with two outputs each.
 
-	// Timer2: Fast mode, non-inverting, top=0xFF, prescale /8
+	// TIMER2: Fast mode, non-inverting, top=0xFF, prescale /8
+
 	// Top set to 8000000 (f_cpu) / 8 (prescale) / 25000 (f_pwm) - 1
 	// TCCR2 = BIT(WGM20) | BIT(WGM21) | BIT(COM21) | BIT(CS21);
 	// OCR2 = 40 - 1; // XXX: OCR2A=top OCR2B=duty
diff --git a/src/bus/pwm.h b/src/bus/pwm.h
index 4920ead..9a8f68f 100644
--- a/src/bus/pwm.h
+++ b/src/bus/pwm.h
@@ -1,20 +1,19 @@
-#ifndef MAD_BUS_PWM_H
-#define MAD_BUS_PWM_H
+#ifndef MAD_CORE_BUS_PWM_H
+#define MAD_CORE_BUS_PWM_H
 
 #include <avr/io.h>
 
-// PWM Devices
-#define FAN01 PD4  // NF-12 Fan Peltier Hot Side Speed
-#define FAN02 PD5  // NF-A8 Fan Peltier Cold Side Speed
-#define FAN03 PD7  // NF-R8 Fan Heating Element Speed
+// Devices
+#define FAN01 PD4  // NF-12 Fan Peltier Hot Side
+#define FAN02 PD5  // NF-A8 Fan Peltier Cold Side
+#define FAN03 PD7  // NF-R8 Fan Heating Element
 
 #define PWM_CYCLE_TOP  (F_CPU / 25000 - 1) // 8 MHz / 25 KHz
-
 #define FAN01_MIN_DUTY (PWM_CYCLE_TOP * 0.2f)
 #define FAN02_MIN_DUTY (PWM_CYCLE_TOP * 0.2f)
 #define FAN03_MIN_DUTY (PWM_CYCLE_TOP * 0.2f)
 
-int PWM_Init(void);
-void PWM_SetValue(int port, int value);
+int   PWM_Init(void);
+void  PWM_SetValue(int port, int value);
 
-#endif // MAD_BUS_PWM_H
+#endif // MAD_CORE_BUS_PWM_H
diff --git a/src/common.h b/src/common.h
index 2e5cb73..f79b699 100644
--- a/src/common.h
+++ b/src/common.h
@@ -1,12 +1,11 @@
 #ifndef MAD_CORE_COMMON_H
 #define MAD_CORE_COMMON_H
 
+#include "common/types.h"
 #include "common/watchdog.h"
 
 #include <stddef.h>
-#include <stdint.h>
 #include <stdarg.h>
-#include <stdbool.h>
 
 #define UNUSED(s)         (void)(s)
 #define BIT(n)            (0x1U << (n))
diff --git a/src/common/common.c b/src/common/common.c
index 900f49b..9107a60 100644
--- a/src/common/common.c
+++ b/src/common/common.c
@@ -1,5 +1,6 @@
 #include "common.h"
 #include "bus/usart.h"
+
 #include <stdio.h>
 
 static void Puts(const char *str)
diff --git a/src/common/types.h b/src/common/types.h
new file mode 100644
index 0000000..9e855c1
--- /dev/null
+++ b/src/common/types.h
@@ -0,0 +1,10 @@
+#ifndef MAD_CORE_COMMON_TYPES_H
+#define MAD_CORE_COMMON_TYPES_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+typedef uint8_t   byte;
+typedef uint16_t  word;
+
+#endif // MAD_CORE_COMMON_TYPES_H
diff --git a/src/common/watchdog.c b/src/common/watchdog.c
index 7334c1e..6e18075 100644
--- a/src/common/watchdog.c
+++ b/src/common/watchdog.c
@@ -43,7 +43,7 @@ void WDT_Enable(void)
 	WDTCR = BIT(WDE) | BIT(WDP2) | BIT(WDP1) | BIT(WDP0);
 }
 
-void WDT_SetTimeoutFlag(unsigned char flag)
+void WDT_SetTimeoutFlag(byte flag)
 {
 	flag = CLAMP(flag, 7, 0);
 
diff --git a/src/common/watchdog.h b/src/common/watchdog.h
index b6e336a..479ef5b 100644
--- a/src/common/watchdog.h
+++ b/src/common/watchdog.h
@@ -1,12 +1,12 @@
 #ifndef MAD_CORE_COMMON_WATCHDOG_H
 #define MAD_CORE_COMMON_WATCHDOG_H
 
-#include <stdbool.h>
+#include "common/types.h"
 
-void WDT_Enable(void);
-void WDT_SetTimeoutFlag(unsigned char flag);
-bool WDT_HasTriggered(void);
-void WDT_Disable(void);
-void WDT_Reset(void);
+void  WDT_Enable(void);
+void  WDT_SetTimeoutFlag(byte flag);
+bool  WDT_HasTriggered(void);
+void  WDT_Disable(void);
+void  WDT_Reset(void);
 
 #endif // MAD_CORE_COMMON_WATCHDOG_H