diff --git a/src/machine/board_stm32f4disco.go b/src/machine/board_stm32f4disco.go
index 7c10b3ed..f1be4814 100644
--- a/src/machine/board_stm32f4disco.go
+++ b/src/machine/board_stm32f4disco.go
@@ -66,3 +66,15 @@ var (
 	}
 	SPI1 = &SPI0
 )
+
+const (
+	I2C0_SCL_PIN = PB6
+	I2C0_SDA_PIN = PB9
+)
+
+var (
+	I2C0 = I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: AF4_I2C1_2_3,
+	}
+)
diff --git a/src/machine/i2c.go b/src/machine/i2c.go
index f4112317..497a0a79 100644
--- a/src/machine/i2c.go
+++ b/src/machine/i2c.go
@@ -1,4 +1,4 @@
-// +build avr nrf sam stm32,!stm32f407,!stm32f7x2,!stm32l5x2,!stm32l0 fe310 k210
+// +build avr nrf sam stm32,!stm32f7x2,!stm32l5x2,!stm32l0 fe310 k210
 
 package machine
 
diff --git a/src/machine/machine_stm32_i2c.go b/src/machine/machine_stm32_i2c.go
index 0a944c7a..fbee11d8 100644
--- a/src/machine/machine_stm32_i2c.go
+++ b/src/machine/machine_stm32_i2c.go
@@ -1,4 +1,4 @@
-// +build stm32,!stm32f103,!stm32f407,!stm32f7x2,!stm32l5x2,!stm32l0
+// +build stm32,!stm32f103,!stm32f7x2,!stm32l5x2,!stm32l0
 
 package machine
 
@@ -151,7 +151,7 @@ func (i2c I2C) Configure(config I2CConfig) error {
 	i2c.Bus.CR1.ClearBits(stm32.I2C_CR1_ENGC | stm32.I2C_CR1_NOSTRETCH)
 
 	// enable I2C interface
-	i2c.Bus.CR1.ClearBits(stm32.I2C_CR1_PE)
+	i2c.Bus.CR1.SetBits(stm32.I2C_CR1_PE)
 
 	return nil
 }
@@ -161,9 +161,13 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 	if err := i2c.controllerTransmit(addr, w); nil != err {
 		return err
 	}
-	if err := i2c.controllerReceive(addr, r); nil != err {
-		return err
+
+	if len(r) > 0 {
+		if err := i2c.controllerReceive(addr, r); nil != err {
+			return err
+		}
 	}
+
 	return nil
 }
 
@@ -173,11 +177,6 @@ func (i2c I2C) controllerTransmit(addr uint16, w []byte) error {
 		return errI2CBusReadyTimeout
 	}
 
-	// ensure peripheral is enabled
-	if !i2c.Bus.CR1.HasBits(stm32.I2C_CR1_PE) {
-		i2c.Bus.CR1.SetBits(stm32.I2C_CR1_PE)
-	}
-
 	// disable POS
 	i2c.Bus.CR1.ClearBits(stm32.I2C_CR1_POS)
 
@@ -256,11 +255,6 @@ func (i2c I2C) controllerReceive(addr uint16, r []byte) error {
 		return errI2CBusReadyTimeout
 	}
 
-	// ensure peripheral is enabled
-	if !i2c.Bus.CR1.HasBits(stm32.I2C_CR1_PE) {
-		i2c.Bus.CR1.SetBits(stm32.I2C_CR1_PE)
-	}
-
 	// disable POS
 	i2c.Bus.CR1.ClearBits(stm32.I2C_CR1_POS)
 
diff --git a/src/machine/machine_stm32f407.go b/src/machine/machine_stm32f407.go
index a0d9e190..c33094f1 100644
--- a/src/machine/machine_stm32f407.go
+++ b/src/machine/machine_stm32f407.go
@@ -120,3 +120,81 @@ func (spi SPI) configurePins(config SPIConfig) {
 	config.SDO.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDO}, spi.AltFuncSelector)
 	config.SDI.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDI}, spi.AltFuncSelector)
 }
+
+// -- I2C ----------------------------------------------------------------------
+
+type I2C struct {
+	Bus             *stm32.I2C_Type
+	AltFuncSelector uint8
+}
+
+func (i2c I2C) configurePins(config I2CConfig) {
+	config.SCL.ConfigureAltFunc(PinConfig{Mode: PinModeI2CSCL}, i2c.AltFuncSelector)
+	config.SDA.ConfigureAltFunc(PinConfig{Mode: PinModeI2CSDA}, i2c.AltFuncSelector)
+}
+
+func (i2c I2C) getFreqRange(config I2CConfig) uint32 {
+	// all I2C interfaces are on APB1 (42 MHz)
+	clock := CPUFrequency() / 4
+	// convert to MHz
+	clock /= 1000000
+	// must be between 2 MHz (or 4 MHz for fast mode (Fm)) and 50 MHz, inclusive
+	var min, max uint32 = 2, 50
+	if config.Frequency > 100000 {
+		min = 4 // fast mode (Fm)
+	}
+	if clock < min {
+		clock = min
+	} else if clock > max {
+		clock = max
+	}
+	return clock << stm32.I2C_CR2_FREQ_Pos
+}
+
+func (i2c I2C) getRiseTime(config I2CConfig) uint32 {
+	// These bits must be programmed with the maximum SCL rise time given in the
+	// I2C bus specification, incremented by 1.
+	// For instance: in Sm mode, the maximum allowed SCL rise time is 1000 ns.
+	// If, in the I2C_CR2 register, the value of FREQ[5:0] bits is equal to 0x08
+	// and PCLK1 = 125 ns, therefore the TRISE[5:0] bits must be programmed with
+	// 09h (1000 ns / 125 ns = 8 + 1)
+	freqRange := i2c.getFreqRange(config)
+	if config.Frequency > 100000 {
+		// fast mode (Fm) adjustment
+		freqRange *= 300
+		freqRange /= 1000
+	}
+	return (freqRange + 1) << stm32.I2C_TRISE_TRISE_Pos
+}
+
+func (i2c I2C) getSpeed(config I2CConfig) uint32 {
+	ccr := func(pclk uint32, freq uint32, coeff uint32) uint32 {
+		return (((pclk - 1) / (freq * coeff)) + 1) & stm32.I2C_CCR_CCR_Msk
+	}
+	sm := func(pclk uint32, freq uint32) uint32 { // standard mode (Sm)
+		if s := ccr(pclk, freq, 2); s < 4 {
+			return 4
+		} else {
+			return s
+		}
+	}
+	fm := func(pclk uint32, freq uint32, duty uint8) uint32 { // fast mode (Fm)
+		if duty == DutyCycle2 {
+			return ccr(pclk, freq, 3)
+		} else {
+			return ccr(pclk, freq, 25) | stm32.I2C_CCR_DUTY
+		}
+	}
+	// all I2C interfaces are on APB1 (42 MHz)
+	clock := CPUFrequency() / 4
+	if config.Frequency <= 100000 {
+		return sm(clock, config.Frequency)
+	} else {
+		s := fm(clock, config.Frequency, config.DutyCycle)
+		if (s & stm32.I2C_CCR_CCR_Msk) == 0 {
+			return 1
+		} else {
+			return s | stm32.I2C_CCR_F_S
+		}
+	}
+}