diff --git a/include/libopencm3/sam3x/pmc.h b/include/libopencm3/sam3x/pmc.h
index b08bf51a..cff7ed0a 100644
--- a/include/libopencm3/sam3x/pmc.h
+++ b/include/libopencm3/sam3x/pmc.h
@@ -125,6 +125,8 @@
 #define PMC_SR_LOCKA			(0x01 << 1)
 #define PMC_SR_MOSCXTS			(0x01 << 0)
 
+extern u32 pmc_mck_frequency;
+
 enum mck_src {
 	MCK_SRC_SLOW = 0,
 	MCK_SRC_MAIN = 1,
@@ -137,5 +139,7 @@ void pmc_xtal_enable(bool en, u8 startup_time);
 void pmc_plla_config(u8 mul, u8 div);
 void pmc_peripheral_clock_enable(u8 pid);
 void pmc_peripheral_clock_disable(u8 pid);
+void pmc_clock_setup_in_xtal_12mhz_out_84mhz(void);
 
 #endif
+
diff --git a/include/libopencm3/sam3x/usart.h b/include/libopencm3/sam3x/usart.h
index 2eb99af0..bf5e4bf9 100644
--- a/include/libopencm3/sam3x/usart.h
+++ b/include/libopencm3/sam3x/usart.h
@@ -196,6 +196,7 @@ enum usart_flowcontrol {
 	USART_FLOWCONTROL_RTS_CTS,
 };
 
+void usart_set_baudrate(u32 usart, u32 baud);
 void usart_set_databits(u32 usart, int bits);
 void usart_set_stopbits(u32 usart, enum usart_stopbits);
 void usart_set_parity(u32 usart, enum usart_parity);
diff --git a/lib/sam3x/pmc.c b/lib/sam3x/pmc.c
index cd0ad245..0086e177 100644
--- a/lib/sam3x/pmc.c
+++ b/lib/sam3x/pmc.c
@@ -18,6 +18,10 @@
  */
 
 #include <libopencm3/sam3x/pmc.h>
+#include <libopencm3/sam3x/eefc.h>
+
+/** Default peripheral clock frequency after reset. */
+u32 pmc_mck_frequency = 4000000;
 
 void pmc_xtal_enable(bool en, u8 startup_time)
 {
@@ -60,3 +64,18 @@ void pmc_mck_set_source(enum mck_src src)
 	while (!(PMC_SR & PMC_SR_MCKRDY));
 }
 
+void pmc_clock_setup_in_xtal_12mhz_out_84mhz(void)
+{
+	eefc_set_latency(4);
+
+	/* 12MHz external xtal, maximum possible startup time */
+	pmc_xtal_enable(true, 0xff);
+	/* Select as main oscillator */
+	CKGR_MOR |= CKGR_MOR_KEY | CKGR_MOR_MOSCSEL;
+	/* Multiply by 7 for 84MHz */
+	pmc_plla_config(7, 1);
+	pmc_mck_set_source(MCK_SRC_PLLA);
+
+	pmc_mck_frequency = 84000000;
+}
+
diff --git a/lib/sam3x/usart.c b/lib/sam3x/usart.c
index ebef382c..012a07e0 100644
--- a/lib/sam3x/usart.c
+++ b/lib/sam3x/usart.c
@@ -18,6 +18,12 @@
  */
 
 #include <libopencm3/sam3x/usart.h>
+#include <libopencm3/sam3x/pmc.h>
+
+void usart_set_baudrate(u32 usart, u32 baud)
+{
+	USART_BRGR(usart) = pmc_mck_frequency / (16 * baud);
+}
 
 void usart_set_databits(u32 usart, int bits)
 {