diff --git a/include/libopenstm32/usart.h b/include/libopenstm32/usart.h
index 237a58f6..422a8936 100644
--- a/include/libopenstm32/usart.h
+++ b/include/libopenstm32/usart.h
@@ -132,6 +132,11 @@
 #define PARITY_ODD			0x02
 #define PARITY_EVEN			0x03
 
+/* CR1_TE/CR1_RE combined values */
+#define MODE_RX				0x01
+#define MODE_TX				0x02
+#define MODE_TX_RX			0x03
+
 /* --- USART_CR2 values ---------------------------------------------------- */
 
 #define CR2_LINEN			(1 << 14) /* LIN mode enable */
@@ -177,4 +182,17 @@
 
 /* TODO */
 
+/* --- Function prototypes ------------------------------------------------- */
+
+void usart_set_baudrate(u32 usart, u32 baud);
+void usart_set_databits(u32 usart, u32 bits);
+void usart_set_stopbits(u32 usart, u32 stopbits);
+void usart_set_parity(u32 usart, u32 parity);
+void usart_set_mode(u32 usart, u32 mode);
+void usart_set_flow_control(u32 usart, u32 flowcontrol);
+void usart_enable(u32 usart);
+void usart_disable(u32 usart);
+void usart_send(u32 usart, u16 data);
+u16 usart_recv(u32 usart);
+
 #endif
diff --git a/lib/usart.c b/lib/usart.c
index 02edd86e..fdcc9321 100644
--- a/lib/usart.c
+++ b/lib/usart.c
@@ -19,5 +19,83 @@
 
 #include <libopenstm32.h>
 
-/* TODO */
+void usart_set_baudrate(u32 usart, u32 baud)
+{
+	u32 clock = 36000000; /* FIXME: Don't hardcode this clock! */
+
+	/* TODO: Document and explain calculation. */
+	USART_BRR(usart) = (u16)((clock << 4) / (baud * 16));
+}
+
+void usart_set_databits(u32 usart, u32 bits)
+{
+	if (bits == 8)
+		USART_CR1(usart) &= ~CR1_M; /* 8 data bits */
+	else
+		USART_CR1(usart) |= CR1_M;  /* 9 data bits */
+}
+
+void usart_set_stopbits(u32 usart, u32 stopbits)
+{
+	u32 reg32;
+
+	reg32 = USART_CR2(usart);
+	reg32 = (reg32 & ~((1 << 13) | (1 << 12))) | (stopbits << 12);
+	USART_CR2(usart) = reg32;
+}
+
+void usart_set_parity(u32 usart, u32 parity)
+{
+	u32 reg32;
+
+	reg32 = USART_CR1(usart);
+	reg32 = (reg32 & ~((1 << 10) | (1 << 9))) | (parity << 9);
+	USART_CR1(usart) = reg32;
+}
+
+void usart_set_mode(u32 usart, u32 mode)
+{
+	u32 reg32;
+
+	reg32 = USART_CR1(usart);
+	reg32 = (reg32 & ~((1 << 3) | (1 << 2))) | (mode << 2);
+	USART_CR1(usart) = reg32;
+}
+
+void usart_set_flow_control(u32 usart, u32 flowcontrol)
+{
+	u32 reg32;
+
+	reg32 = USART_CR3(usart);
+	reg32 = (reg32 & ~((1 << 9) | (1 << 8))) | (flowcontrol << 2);
+	USART_CR3(usart) = reg32;
+}
+
+void usart_enable(u32 usart)
+{
+	USART_CR1(usart) |= CR1_UE;
+}
+
+void usart_disable(u32 usart)
+{
+	USART_CR1(usart) &= ~CR1_UE;
+}
+
+void usart_send(u32 usart, u16 data)
+{
+	/* Send data. */
+	USART_DR(usart) = (data & 0x1ff);
+
+	/* Wait until the data has been transferred into the shift register. */
+	while ((USART_SR(usart) & SR_TXE) == 0);
+}
+
+u16 usart_recv(u32 usart)
+{
+	/* Wait until the data is ready to be received. */
+	while ((USART_SR(usart) & SR_RXNE) == 0);
+
+	/* Receive data. */
+	return USART_DR(usart) & 0x1ff;
+}