diff --git a/hardware0.cpp b/hardware0.cpp
new file mode 100644
index 0000000..220f9b4
--- /dev/null
+++ b/hardware0.cpp
@@ -0,0 +1,30 @@
+#include "hardware0.hpp"
+
+#include <avr/interrupt.h>
+
+namespace uart {
+namespace detail {
+
+#if defined(__AVR_ATmega1284P__)
+
+void (*fnRx0IntHandler)() = nullptr;
+void (*fnDataReg0EmptyIntHandler)() = nullptr;
+
+ISR(USART0_RX_vect)
+{
+	if (fnRx0IntHandler)
+		fnRx0IntHandler();
+}
+
+ISR(USART0_UDRE_vect)
+{
+	if (fnDataReg0EmptyIntHandler)
+		fnDataReg0EmptyIntHandler();
+}
+
+#else
+#error "This chip is not supported"
+#endif
+
+} // namespace detail
+} // namespace uart
diff --git a/hardware0.hpp b/hardware0.hpp
index ace10ba..8ce0629 100644
--- a/hardware0.hpp
+++ b/hardware0.hpp
@@ -63,20 +63,8 @@ constexpr int operator<<(const int &lhs, const ControlFlagsB0 &rhs) { return lhs
 constexpr int operator<<(const int &lhs, const ControlFlagsC0 &rhs) { return lhs << static_cast<int>(rhs); }
 // clang-format on
 
-static void (*fnRx0IntHandler)() = nullptr;
-static void (*fnDataReg0EmptyIntHandler)() = nullptr;
-
-ISR(USART0_RX_vect)
-{
-	if (fnRx0IntHandler)
-		fnRx0IntHandler();
-}
-
-ISR(USART0_UDRE_vect)
-{
-	if (fnDataReg0EmptyIntHandler)
-		fnDataReg0EmptyIntHandler();
-}
+extern void (*fnRx0IntHandler)();
+extern void (*fnDataReg0EmptyIntHandler)();
 
 #else
 #error "This chip is not supported"
diff --git a/hardware1.cpp b/hardware1.cpp
new file mode 100644
index 0000000..f7b70cc
--- /dev/null
+++ b/hardware1.cpp
@@ -0,0 +1,30 @@
+#include "hardware1.hpp"
+
+#include <avr/interrupt.h>
+
+namespace uart {
+namespace detail {
+
+#if defined(__AVR_ATmega1284P__)
+
+void (*fnRx1IntHandler)() = nullptr;
+void (*fnDataReg1EmptyIntHandler)() = nullptr;
+
+ISR(USART1_RX_vect)
+{
+	if (fnRx1IntHandler)
+		fnRx1IntHandler();
+}
+
+ISR(USART1_UDRE_vect)
+{
+	if (fnDataReg1EmptyIntHandler)
+		fnDataReg1EmptyIntHandler();
+}
+
+#else
+#error "This chip is not supported"
+#endif
+
+} // namespace detail
+} // namespace uart
diff --git a/hardware1.hpp b/hardware1.hpp
index f3e8572..5528b32 100644
--- a/hardware1.hpp
+++ b/hardware1.hpp
@@ -63,20 +63,8 @@ constexpr int operator<<(const int &lhs, const ControlFlagsB1 &rhs) { return lhs
 constexpr int operator<<(const int &lhs, const ControlFlagsC1 &rhs) { return lhs << static_cast<int>(rhs); }
 // clang-format on
 
-static void (*fnRx1IntHandler)() = nullptr;
-static void (*fnDataReg1EmptyIntHandler)() = nullptr;
-
-ISR(USART1_RX_vect)
-{
-	if (fnRx1IntHandler)
-		fnRx1IntHandler();
-}
-
-ISR(USART1_UDRE_vect)
-{
-	if (fnDataReg1EmptyIntHandler)
-		fnDataReg1EmptyIntHandler();
-}
+extern void (*fnRx1IntHandler)();
+extern void (*fnDataReg1EmptyIntHandler)();
 
 #define HAS_UART1