diff --git a/io.hpp b/io.hpp
index b9c29f2..8bbe3db 100644
--- a/io.hpp
+++ b/io.hpp
@@ -3,6 +3,7 @@
 #include <stdint.h>
 
 #include <avr/io.h>
+#include <avr/sfr_defs.h>
 
 //////////////////////////////////////////////////////////////////////////
 // Preprocessor defines
@@ -125,46 +126,60 @@ enum class Bus {
 
 namespace detail {
 
+/*
+The following works in avr-gcc 5.4.0, but is not legal C++, because ptr's are not legal constexpr's
+  constexpr auto *foo = ptr;
+
+Workaround is to store the the address of the ptr in a uintptr_t and reinterpret_cast it at call site
+For this to work we need to temporarily disable the _SFR_IO8 macro so that the register macro just gives the address
+*/
+
+#undef _SFR_IO8
+#define _SFR_IO8
+
 #ifdef PORT_A_AVAILABLE
-static constexpr volatile uint8_t *PORT_A_DIR_REG = &DDRA;
-static constexpr volatile uint8_t *PORT_A_OUTPUT_REG = &PORTA;
-static constexpr volatile uint8_t *PORT_A_INPUT_REG = &PINA;
+static constexpr uintptr_t PORT_A_DIR_REG_ADDR = DDRA + __SFR_OFFSET;
+static constexpr uintptr_t PORT_A_OUTPUT_REG_ADDR = PORTA + __SFR_OFFSET;
+static constexpr uintptr_t PORT_A_INPUT_REG_ADDR = PINA + __SFR_OFFSET;
 #else
-static constexpr volatile uint8_t *PORT_A_DIR_REG = nullptr;
-static constexpr volatile uint8_t *PORT_A_OUTPUT_REG = nullptr;
-static constexpr volatile uint8_t *PORT_A_INPUT_REG = nullptr;
+static constexpr uintptr_t PORT_A_DIR_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_A_OUTPUT_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_A_INPUT_REG_ADDR = nullptr;
 #endif
 
 #ifdef PORT_B_AVAILABLE
-static constexpr volatile uint8_t *PORT_B_DIR_REG = &DDRB;
-static constexpr volatile uint8_t *PORT_B_OUTPUT_REG = &PORTB;
-static constexpr volatile uint8_t *PORT_B_INPUT_REG = &PINB;
+static constexpr uintptr_t PORT_B_DIR_REG_ADDR = DDRB + __SFR_OFFSET;
+static constexpr uintptr_t PORT_B_OUTPUT_REG_ADDR = PORTB + __SFR_OFFSET;
+static constexpr uintptr_t PORT_B_INPUT_REG_ADDR = PINB + __SFR_OFFSET;
 #else
-static constexpr volatile uint8_t *PORT_B_DIR_REG = nullptr;
-static constexpr volatile uint8_t *PORT_B_OUTPUT_REG = nullptr;
-static constexpr volatile uint8_t *PORT_B_INPUT_REG = nullptr;
+static constexpr uintptr_t PORT_B_DIR_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_B_OUTPUT_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_B_INPUT_REG_ADDR = nullptr;
 #endif
 
 #ifdef PORT_C_AVAILABLE
-static constexpr volatile uint8_t *PORT_C_DIR_REG = &DDRC;
-static constexpr volatile uint8_t *PORT_C_OUTPUT_REG = &PORTC;
-static constexpr volatile uint8_t *PORT_C_INPUT_REG = &PINC;
+static constexpr uintptr_t PORT_C_DIR_REG_ADDR = DDRC + __SFR_OFFSET;
+static constexpr uintptr_t PORT_C_OUTPUT_REG_ADDR = PORTC + __SFR_OFFSET;
+static constexpr uintptr_t PORT_C_INPUT_REG_ADDR = PINC + __SFR_OFFSET;
 #else
-static constexpr volatile uint8_t *PORT_C_DIR_REG = nullptr;
-static constexpr volatile uint8_t *PORT_C_OUTPUT_REG = nullptr;
-static constexpr volatile uint8_t *PORT_C_INPUT_REG = nullptr;
+static constexpr uintptr_t PORT_C_DIR_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_C_OUTPUT_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_C_INPUT_REG_ADDR = nullptr;
 #endif
 
 #ifdef PORT_D_AVAILABLE
-static constexpr volatile uint8_t *PORT_D_DIR_REG = &DDRD;
-static constexpr volatile uint8_t *PORT_D_OUTPUT_REG = &PORTD;
-static constexpr volatile uint8_t *PORT_D_INPUT_REG = &PIND;
+static constexpr uintptr_t PORT_D_DIR_REG_ADDR = DDRD + __SFR_OFFSET;
+static constexpr uintptr_t PORT_D_OUTPUT_REG_ADDR = PORTD + __SFR_OFFSET;
+static constexpr uintptr_t PORT_D_INPUT_REG_ADDR = PIND + __SFR_OFFSET;
 #else
-static constexpr volatile uint8_t *PORT_D_DIR_REG = nullptr;
-static constexpr volatile uint8_t *PORT_D_OUTPUT_REG = nullptr;
-static constexpr volatile uint8_t *PORT_D_INPUT_REG = nullptr;
+static constexpr uintptr_t PORT_D_DIR_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_D_OUTPUT_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_D_INPUT_REG_ADDR = nullptr;
 #endif
 
+#undef _SFR_IO8
+#define _SFR_IO8(io_addr) _MMIO_BYTE((io_addr) + __SFR_OFFSET)
+
 static constexpr auto getBus(const P pin)
 {
 	// Upper 4 bits of pin encode which port this pin is on
@@ -183,13 +198,13 @@ static constexpr auto getDDR(const Bus bus)
 {
 	switch (static_cast<uint8_t>(bus)) {
 	case 0: // Bus::A
-		return PORT_A_DIR_REG;
+		return PORT_A_DIR_REG_ADDR;
 	case 1: // Bus::B
-		return PORT_B_DIR_REG;
+		return PORT_B_DIR_REG_ADDR;
 	case 2: // Bus::C
-		return PORT_C_DIR_REG;
+		return PORT_C_DIR_REG_ADDR;
 	case 3: // Bus::D
-		return PORT_D_DIR_REG;
+		return PORT_D_DIR_REG_ADDR;
 	}
 }
 
@@ -197,13 +212,13 @@ static constexpr auto getPORT(const Bus bus)
 {
 	switch (static_cast<uint8_t>(bus)) {
 	case 0: // Bus::A
-		return PORT_A_OUTPUT_REG;
+		return PORT_A_OUTPUT_REG_ADDR;
 	case 1: // Bus::B
-		return PORT_B_OUTPUT_REG;
+		return PORT_B_OUTPUT_REG_ADDR;
 	case 2: // Bus::C
-		return PORT_C_OUTPUT_REG;
+		return PORT_C_OUTPUT_REG_ADDR;
 	case 3: // Bus::D
-		return PORT_D_OUTPUT_REG;
+		return PORT_D_OUTPUT_REG_ADDR;
 	}
 }
 
@@ -211,16 +226,22 @@ static constexpr auto getPIN(const Bus bus)
 {
 	switch (static_cast<uint8_t>(bus)) {
 	case 0: // Bus::A
-		return PORT_A_INPUT_REG;
+		return PORT_A_INPUT_REG_ADDR;
 	case 1: // Bus::B
-		return PORT_B_INPUT_REG;
+		return PORT_B_INPUT_REG_ADDR;
 	case 2: // Bus::C
-		return PORT_C_INPUT_REG;
+		return PORT_C_INPUT_REG_ADDR;
 	case 3: // Bus::D
-		return PORT_D_INPUT_REG;
+		return PORT_D_INPUT_REG_ADDR;
 	}
 }
 
+template <uintptr_t Address>
+static inline volatile uint8_t *getRegPtr()
+{
+	return reinterpret_cast<volatile uint8_t *>(Address);
+}
+
 } // namespace detail
 
 //////////////////////////////////////////////////////////////////////////
@@ -245,9 +266,9 @@ class Pin {
 		constexpr auto pinBit = detail::getPinBit(pin);
 
 		if (dir == Dir::IN)
-			*dirReg &= ~(1 << pinBit);
+			*detail::getRegPtr<dirReg>() &= ~(1 << pinBit);
 		else if (dir == Dir::OUT)
-			*dirReg |= (1 << pinBit);
+			*detail::getRegPtr<dirReg>() |= (1 << pinBit);
 	}
 
 	static inline void pullup(const bool enable) FORCE_INLINE
@@ -257,9 +278,9 @@ class Pin {
 		constexpr auto pinBit = detail::getPinBit(pin);
 
 		if (enable)
-			*portReg |= (1 << pinBit);
+			*detail::getRegPtr<portReg>() |= (1 << pinBit);
 		else
-			*portReg &= ~(1 << pinBit);
+			*detail::getRegPtr<portReg>() &= ~(1 << pinBit);
 	}
 
 	static inline void write(const bool value) FORCE_INLINE
@@ -269,9 +290,9 @@ class Pin {
 		constexpr auto pinBit = detail::getPinBit(pin);
 
 		if (value)
-			*portReg |= (1 << pinBit);
+			*detail::getRegPtr<portReg>() |= (1 << pinBit);
 		else
-			*portReg &= ~(1 << pinBit);
+			*detail::getRegPtr<portReg>() &= ~(1 << pinBit);
 	}
 
 	static inline void toggle() FORCE_INLINE
@@ -281,13 +302,13 @@ class Pin {
 		constexpr auto pinReg = detail::getPIN(bus);
 		constexpr auto pinBit = detail::getPinBit(pin);
 
-		*pinReg |= (1 << pinBit);
+		*detail::getRegPtr<pinReg>() |= (1 << pinBit);
 #else
 		constexpr auto bus = detail::getBus(pin);
 		constexpr auto portReg = detail::getPORT(bus);
 		constexpr auto pinBit = detail::getPinBit(pin);
 
-		*portReg ^= (1 << pinBit);
+		*detail::getRegPtr<pinReg>() ^= (1 << pinBit);
 #endif
 	}
 
@@ -297,7 +318,7 @@ class Pin {
 		constexpr auto pinReg = detail::getPIN(bus);
 		constexpr auto pinBit = detail::getPinBit(pin);
 
-		if (*pinReg >> pinBit & 1)
+		if (*detail::getRegPtr<pinReg>() >> pinBit & 1)
 			return true;
 
 		return false;
@@ -335,9 +356,9 @@ class Port {
 		constexpr auto dirReg = detail::getDDR(port);
 
 		if (dir == Dir::IN)
-			*dirReg = 0x00;
+			*detail::getRegPtr<dirReg>() = 0x00;
 		else if (dir == Dir::OUT)
-			*dirReg = 0xFF;
+			*detail::getRegPtr<dirReg>() = 0xFF;
 	}
 
 	static inline void pullup(const bool enable) FORCE_INLINE
@@ -345,16 +366,16 @@ class Port {
 		constexpr auto portReg = detail::getPORT(port);
 
 		if (enable)
-			*portReg = 0xFF;
+			*detail::getRegPtr<portReg>() = 0xFF;
 		else
-			*portReg = 0x00;
+			*detail::getRegPtr<portReg>() = 0x00;
 	}
 
 	static inline void write(const uint8_t value) FORCE_INLINE
 	{
 		constexpr auto portReg = detail::getPORT(port);
 
-		*portReg = value;
+		*detail::getRegPtr<portReg>() = value;
 	}
 
 	static inline void invert() FORCE_INLINE
@@ -362,11 +383,11 @@ class Port {
 #ifdef HARDWARE_TOGGLE
 		constexpr auto pinReg = detail::getPIN(port);
 
-		*pinReg = 0xFF;
+		*detail::getRegPtr<pinReg>() = 0xFF;
 #else
 		constexpr auto portReg = detail::getPORT(port);
 
-		*portReg = ~(*portReg);
+		*detail::getRegPtr<portReg>() = ~(*portReg);
 #endif
 	}
 
@@ -374,7 +395,7 @@ class Port {
 	{
 		constexpr auto pinReg = detail::getPIN(port);
 
-		return *pinReg;
+		return *detail::getRegPtr<pinReg>();
 	}
 
 	inline Port &operator=(const uint8_t value) FORCE_INLINE