4 files changed, 18 insertions, 3 deletions
diff --git a/Makefile b/Makefile
index ea5d872..ef5ba35 100644
--- a/Makefile
+++ b/Makefile
@@ -17,12 +17,17 @@ CFLAGS = -std=c11 $(WARNINGS) -O2 -flto -MMD -MP -ffreestanding -nostdlib
 LDFLAGS = -T layout.ld -O2 -flto -ffreestanding -nostdlib
 ASFLAGS = $(TARGET_ARCH)
 
-OBJ := vectors.o flashconf.o crt0.o setup.o fmk.o lib/le.o pit.o uart.o \
-	usb/endpt0.o usb/endpt1.o usb/txhandler.o usb/usb.o
+OBJ := vectors.o flashconf.o crt0.o setup.o fmk.o lib/le.o pit.o \
+	usb/endpt0.o usb/endpt1.o usb/txhandler.o usb/usb.o weak.o
 
 include $(MK20DX256)/mk20dx256.mk
 CPPFLAGS += $(mk20dx256_CPPFLAGS)
 
+ifeq ("$(WITH_UART)", "yes")
+	CPPFLAGS += -DWITH_UART
+	OBJ += uart.o
+endif
+
 %.bin: %
 	$(OBJCOPY) -O binary $< $@
 
diff --git a/uart.c b/uart.c
index 3ead880..ab3ca89 100644
--- a/uart.c
+++ b/uart.c
@@ -212,6 +212,7 @@ void uart_printf(const char *fmt, ...)
 	va_end(ap);
 }
 
+void uart0_isr(void);
 void uart0_isr(void)
 {
 	int avail, start, end, tosend;
diff --git a/uart.h b/uart.h
index 5ff2d79..b60b250 100644
--- a/uart.h
+++ b/uart.h
@@ -19,10 +19,16 @@
 #ifndef FMK_UART_H
 #define FMK_UART_H
 
+#ifdef WITH_UART
 void uart_setup(void);
 void uart_putchar(int c);
 void uart_printf(const char *fmt, ...);
 void uart_puts(const char *s);
-void uart0_isr(void);
+#else
+static inline void uart_setup(void) { }
+static inline void uart_putchar(int c) { (void)c; }
+static inline void uart_printf(const char *fmt, ...) { (void)fmt; }
+static inline void uart_puts(const char *s) { (void)s; }
+#endif
 
 #endif /* FMK_UART_H */
diff --git a/weak.c b/weak.c
new file mode 100644
index 0000000..8d8a726
--- /dev/null
+++ b/weak.c
@@ -0,0 +1,3 @@
+void uart0_isr(void);
+__attribute__ ((weak))
+void uart0_isr(void) { }