diff --git a/src/machine/machine_fe310.go b/src/machine/machine_fe310.go
index ebd85971..ffad20de 100644
--- a/src/machine/machine_fe310.go
+++ b/src/machine/machine_fe310.go
@@ -9,7 +9,7 @@ import (
 )
 
 func CPUFrequency() uint32 {
-	return 16000000
+	return 320000000 // 320MHz
 }
 
 const (
@@ -61,9 +61,17 @@ var (
 )
 
 func (uart *UART) Configure(config UARTConfig) {
-	// Assuming a 16Mhz Crystal (which is Y1 on the HiFive1), the divisor for a
-	// 115200 baud rate is 138.
-	sifive.UART0.DIV.Set(138)
+	if config.BaudRate == 0 {
+		config.BaudRate = 115200
+	}
+	// The divisor is:
+	//   fbaud = fin / (div + 1)
+	// Restating to get the divisor:
+	//   div = fin / fbaud - 1
+	// But we're using integers, so we should take care of rounding:
+	//   div = (fin + fbaud/2) / fbaud - 1
+	divisor := (CPUFrequency()+config.BaudRate/2)/config.BaudRate - 1
+	sifive.UART0.DIV.Set(divisor)
 	sifive.UART0.TXCTRL.Set(sifive.UART_TXCTRL_ENABLE)
 	sifive.UART0.RXCTRL.Set(sifive.UART_RXCTRL_ENABLE)
 	sifive.UART0.IE.Set(sifive.UART_IE_RXWM) // enable the receive interrupt (only)
diff --git a/src/runtime/runtime_fe310.go b/src/runtime/runtime_fe310.go
index 2163fb0f..5cfa7a69 100644
--- a/src/runtime/runtime_fe310.go
+++ b/src/runtime/runtime_fe310.go
@@ -79,12 +79,12 @@ func handleInterrupt() {
 
 // initPeripherals configures periperhals the way the runtime expects them.
 func initPeripherals() {
-	// Make sure the HFROSC is on
-	sifive.PRCI.HFROSCCFG.SetBits(sifive.PRCI_HFROSCCFG_ENABLE)
-
-	// Run off 16 MHz Crystal for accuracy.
-	sifive.PRCI.PLLCFG.SetBits(sifive.PRCI_PLLCFG_REFSEL | sifive.PRCI_PLLCFG_BYPASS)
-	sifive.PRCI.PLLCFG.SetBits(sifive.PRCI_PLLCFG_SEL)
+	// Configure PLL to output 320MHz.
+	//   R=2:  divide 16MHz to 8MHz
+	//   F=80: multiply 8MHz by 80 to get 640MHz (80/2-1=39)
+	//   Q=2:  divide 640MHz by 2 to get 320MHz
+	// This makes the main CPU run at 320MHz.
+	sifive.PRCI.PLLCFG.Set(sifive.PRCI_PLLCFG_PLLR_R2<<sifive.PRCI_PLLCFG_PLLR_Pos | 39<<sifive.PRCI_PLLCFG_PLLF_Pos | sifive.PRCI_PLLCFG_PLLQ_Q2<<sifive.PRCI_PLLCFG_PLLQ_Pos | sifive.PRCI_PLLCFG_SEL | sifive.PRCI_PLLCFG_REFSEL)
 
 	// Turn off HFROSC to save power
 	sifive.PRCI.HFROSCCFG.ClearBits(sifive.PRCI_HFROSCCFG_ENABLE)