diff --git a/src/device/arm/arm.go b/src/device/arm/arm.go
index fcac1e57..21ba3bbd 100644
--- a/src/device/arm/arm.go
+++ b/src/device/arm/arm.go
@@ -35,6 +35,8 @@ import (
 	"unsafe"
 )
 
+var errCycleCountTooLarge = errors.New("requested cycle count is too large, overflows 24 bit counter")
+
 // Run the given assembly code. The code will be marked as having side effects,
 // as it doesn't produce output and thus would normally be eliminated by the
 // optimizer.
@@ -232,7 +234,7 @@ func SetupSystemTimer(cyclecount uint32) error {
 	}
 	if cyclecount&SYST_RVR_RELOAD_Msk != cyclecount {
 		// The cycle refresh register is only 24 bits wide.  The user-specified value will overflow.
-		return errors.New("requested cycle count is too large, overflows 24 bit counter")
+		return errCycleCountTooLarge
 	}
 
 	// set refresh count
diff --git a/src/machine/i2c.go b/src/machine/i2c.go
index 25d3180f..977c9bad 100644
--- a/src/machine/i2c.go
+++ b/src/machine/i2c.go
@@ -2,12 +2,27 @@
 
 package machine
 
+import (
+	"errors"
+)
+
 // TWI_FREQ is the I2C bus speed. Normally either 100 kHz, or 400 kHz for high-speed bus.
 const (
 	TWI_FREQ_100KHZ = 100000
 	TWI_FREQ_400KHZ = 400000
 )
 
+var (
+	errI2CWriteTimeout       = errors.New("I2C timeout during write")
+	errI2CReadTimeout        = errors.New("I2C timeout during read")
+	errI2CBusReadyTimeout    = errors.New("I2C timeout on bus ready")
+	errI2CSignalStartTimeout = errors.New("I2C timeout on signal start")
+	errI2CSignalReadTimeout  = errors.New("I2C timeout on signal read")
+	errI2CSignalStopTimeout  = errors.New("I2C timeout on signal stop")
+	errI2CAckExpected        = errors.New("I2C error: expected ACK not NACK")
+	errI2CBusError           = errors.New("I2C bus error")
+)
+
 // WriteRegister transmits first the register and then the data to the
 // peripheral device.
 //
diff --git a/src/machine/machine_atsamd21.go b/src/machine/machine_atsamd21.go
index 86491195..cd83b7b4 100644
--- a/src/machine/machine_atsamd21.go
+++ b/src/machine/machine_atsamd21.go
@@ -10,7 +10,6 @@ package machine
 import (
 	"device/arm"
 	"device/sam"
-	"errors"
 	"runtime/interrupt"
 	"unsafe"
 )
@@ -549,13 +548,13 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 		for !i2c.Bus.INTFLAG.HasBits(sam.SERCOM_I2CM_INTFLAG_MB) {
 			timeout--
 			if timeout == 0 {
-				return errors.New("I2C timeout on ready to write data")
+				return errI2CWriteTimeout
 			}
 		}
 
 		// ACK received (0: ACK, 1: NACK)
 		if i2c.Bus.STATUS.HasBits(sam.SERCOM_I2CM_STATUS_RXNACK) {
-			return errors.New("I2C write error: expected ACK not NACK")
+			return errI2CAckExpected
 		}
 
 		// write data
@@ -581,13 +580,13 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			// In that case, send a stop condition and return error.
 			if i2c.Bus.INTFLAG.HasBits(sam.SERCOM_I2CM_INTFLAG_MB) {
 				i2c.Bus.CTRLB.SetBits(wireCmdStop << sam.SERCOM_I2CM_CTRLB_CMD_Pos) // Stop condition
-				return errors.New("I2C read error: expected ACK not NACK")
+				return errI2CAckExpected
 			}
 		}
 
 		// ACK received (0: ACK, 1: NACK)
 		if i2c.Bus.STATUS.HasBits(sam.SERCOM_I2CM_STATUS_RXNACK) {
-			return errors.New("I2C read error: expected ACK not NACK")
+			return errI2CAckExpected
 		}
 
 		// read first byte
@@ -624,16 +623,16 @@ func (i2c I2C) WriteByte(data byte) error {
 	for !i2c.Bus.INTFLAG.HasBits(sam.SERCOM_I2CM_INTFLAG_MB) {
 		// check for bus error
 		if sam.SERCOM3_I2CM.STATUS.HasBits(sam.SERCOM_I2CM_STATUS_BUSERR) {
-			return errors.New("I2C bus error")
+			return errI2CBusError
 		}
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C timeout on write data")
+			return errI2CWriteTimeout
 		}
 	}
 
 	if i2c.Bus.STATUS.HasBits(sam.SERCOM_I2CM_STATUS_RXNACK) {
-		return errors.New("I2C write error: expected ACK not NACK")
+		return errI2CAckExpected
 	}
 
 	return nil
@@ -652,7 +651,7 @@ func (i2c I2C) sendAddress(address uint16, write bool) error {
 		!i2c.Bus.STATUS.HasBits(wireOwnerState<<sam.SERCOM_I2CM_STATUS_BUSSTATE_Pos) {
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C timeout on bus ready")
+			return errI2CBusReadyTimeout
 		}
 	}
 	i2c.Bus.ADDR.Set(uint32(data))
@@ -666,7 +665,7 @@ func (i2c I2C) signalStop() error {
 	for i2c.Bus.SYNCBUSY.HasBits(sam.SERCOM_I2CM_SYNCBUSY_SYSOP) {
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C timeout on signal stop")
+			return errI2CSignalStopTimeout
 		}
 	}
 	return nil
@@ -678,7 +677,7 @@ func (i2c I2C) signalRead() error {
 	for i2c.Bus.SYNCBUSY.HasBits(sam.SERCOM_I2CM_SYNCBUSY_SYSOP) {
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C timeout on signal read")
+			return errI2CSignalReadTimeout
 		}
 	}
 	return nil
@@ -1286,7 +1285,7 @@ func (usbcdc USBCDC) WriteByte(c byte) error {
 		for (getEPINTFLAG(usb_CDC_ENDPOINT_IN) & sam.USB_DEVICE_EPINTFLAG_TRCPT1) == 0 {
 			timeout--
 			if timeout == 0 {
-				return errors.New("USBCDC write byte timeout")
+				return errUSBCDCWriteByteTimeout
 			}
 		}
 	}
diff --git a/src/machine/machine_atsamd51.go b/src/machine/machine_atsamd51.go
index 3879f037..9270ed34 100644
--- a/src/machine/machine_atsamd51.go
+++ b/src/machine/machine_atsamd51.go
@@ -10,7 +10,6 @@ package machine
 import (
 	"device/arm"
 	"device/sam"
-	"errors"
 	"runtime/interrupt"
 	"unsafe"
 )
@@ -925,13 +924,13 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 		for !i2c.Bus.INTFLAG.HasBits(sam.SERCOM_I2CM_INTFLAG_MB) {
 			timeout--
 			if timeout == 0 {
-				return errors.New("I2C timeout on ready to write data")
+				return errI2CWriteTimeout
 			}
 		}
 
 		// ACK received (0: ACK, 1: NACK)
 		if i2c.Bus.STATUS.HasBits(sam.SERCOM_I2CM_STATUS_RXNACK) {
-			return errors.New("I2C write error: expected ACK not NACK")
+			return errI2CAckExpected
 		}
 
 		// write data
@@ -957,13 +956,13 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			// In that case, send a stop condition and return error.
 			if i2c.Bus.INTFLAG.HasBits(sam.SERCOM_I2CM_INTFLAG_MB) {
 				i2c.Bus.CTRLB.SetBits(wireCmdStop << sam.SERCOM_I2CM_CTRLB_CMD_Pos) // Stop condition
-				return errors.New("I2C read error: expected ACK not NACK")
+				return errI2CAckExpected
 			}
 		}
 
 		// ACK received (0: ACK, 1: NACK)
 		if i2c.Bus.STATUS.HasBits(sam.SERCOM_I2CM_STATUS_RXNACK) {
-			return errors.New("I2C read error: expected ACK not NACK")
+			return errI2CAckExpected
 		}
 
 		// read first byte
@@ -1000,16 +999,16 @@ func (i2c I2C) WriteByte(data byte) error {
 	for !i2c.Bus.INTFLAG.HasBits(sam.SERCOM_I2CM_INTFLAG_MB) {
 		// check for bus error
 		if i2c.Bus.STATUS.HasBits(sam.SERCOM_I2CM_STATUS_BUSERR) {
-			return errors.New("I2C bus error")
+			return errI2CBusError
 		}
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C timeout on write data")
+			return errI2CWriteTimeout
 		}
 	}
 
 	if i2c.Bus.STATUS.HasBits(sam.SERCOM_I2CM_STATUS_RXNACK) {
-		return errors.New("I2C write error: expected ACK not NACK")
+		return errI2CAckExpected
 	}
 
 	return nil
@@ -1028,7 +1027,7 @@ func (i2c I2C) sendAddress(address uint16, write bool) error {
 		!i2c.Bus.STATUS.HasBits(wireOwnerState<<sam.SERCOM_I2CM_STATUS_BUSSTATE_Pos) {
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C timeout on bus ready")
+			return errI2CBusReadyTimeout
 		}
 	}
 	i2c.Bus.ADDR.Set(uint32(data))
@@ -1042,7 +1041,7 @@ func (i2c I2C) signalStop() error {
 	for i2c.Bus.SYNCBUSY.HasBits(sam.SERCOM_I2CM_SYNCBUSY_SYSOP) {
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C timeout on signal stop")
+			return errI2CSignalStopTimeout
 		}
 	}
 	return nil
@@ -1054,7 +1053,7 @@ func (i2c I2C) signalRead() error {
 	for i2c.Bus.SYNCBUSY.HasBits(sam.SERCOM_I2CM_SYNCBUSY_SYSOP) {
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C timeout on signal read")
+			return errI2CSignalReadTimeout
 		}
 	}
 	return nil
@@ -1455,7 +1454,7 @@ func (usbcdc USBCDC) WriteByte(c byte) error {
 		for (getEPINTFLAG(usb_CDC_ENDPOINT_IN) & sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1) == 0 {
 			timeout--
 			if timeout == 0 {
-				return errors.New("USBCDC write byte timeout")
+				return errUSBCDCWriteByteTimeout
 			}
 		}
 	}
diff --git a/src/machine/machine_fe310.go b/src/machine/machine_fe310.go
index 0a5048f5..f2de1092 100644
--- a/src/machine/machine_fe310.go
+++ b/src/machine/machine_fe310.go
@@ -4,7 +4,6 @@ package machine
 
 import (
 	"device/sifive"
-	"errors"
 	"runtime/interrupt"
 )
 
@@ -195,8 +194,6 @@ type I2CConfig struct {
 	SDA       Pin
 }
 
-var i2cAckExpectedError error = errors.New("I2C write error: expected ACK not NACK")
-
 // Configure is intended to setup the I2C interface.
 func (i2c I2C) Configure(config I2CConfig) error {
 	var i2cClockFrequency uint32 = 32000000
@@ -238,7 +235,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 
 		// ACK received (0: ACK, 1: NACK)
 		if i2c.Bus.CR_SR.HasBits(sifive.I2C_SR_RX_ACK) {
-			return i2cAckExpectedError
+			return errI2CAckExpected
 		}
 
 		// write data
@@ -255,7 +252,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 
 		// ACK received (0: ACK, 1: NACK)
 		if i2c.Bus.CR_SR.HasBits(sifive.I2C_SR_RX_ACK) {
-			return i2cAckExpectedError
+			return errI2CAckExpected
 		}
 
 		// read first byte
@@ -290,7 +287,7 @@ func (i2c I2C) writeByte(data byte) error {
 
 	// ACK received (0: ACK, 1: NACK)
 	if i2c.Bus.CR_SR.HasBits(sifive.I2C_SR_RX_ACK) {
-		return i2cAckExpectedError
+		return errI2CAckExpected
 	}
 
 	return nil
diff --git a/src/machine/machine_stm32f103xx.go b/src/machine/machine_stm32f103xx.go
index 70cdc6b2..0ec3dccc 100644
--- a/src/machine/machine_stm32f103xx.go
+++ b/src/machine/machine_stm32f103xx.go
@@ -6,7 +6,6 @@ package machine
 
 import (
 	"device/stm32"
-	"errors"
 	"runtime/interrupt"
 	"unsafe"
 )
@@ -343,7 +342,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			for !i2c.Bus.SR2.HasBits(stm32.I2C_SR2_MSL | stm32.I2C_SR2_BUSY) {
 				timeout--
 				if timeout == 0 {
-					return errors.New("I2C timeout on read clear address")
+					return errI2CWriteTimeout
 				}
 			}
 
@@ -354,7 +353,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_RxNE) {
 				timeout--
 				if timeout == 0 {
-					return errors.New("I2C timeout on read 1 byte")
+					return errI2CReadTimeout
 				}
 			}
 
@@ -382,7 +381,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			for !i2c.Bus.SR2.HasBits(stm32.I2C_SR2_MSL | stm32.I2C_SR2_BUSY) {
 				timeout--
 				if timeout == 0 {
-					return errors.New("I2C timeout on read clear address")
+					return errI2CWriteTimeout
 				}
 			}
 
@@ -394,7 +393,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_BTF) {
 				timeout--
 				if timeout == 0 {
-					return errors.New("I2C timeout on read 2 bytes")
+					return errI2CReadTimeout
 				}
 			}
 
@@ -428,7 +427,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			for !i2c.Bus.SR2.HasBits(stm32.I2C_SR2_MSL | stm32.I2C_SR2_BUSY) {
 				timeout--
 				if timeout == 0 {
-					return errors.New("I2C timeout on read clear address")
+					return errI2CWriteTimeout
 				}
 			}
 
@@ -440,8 +439,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_BTF) {
 				timeout--
 				if timeout == 0 {
-					println("I2C timeout on read 3 bytes")
-					return errors.New("I2C timeout on read 3 bytes")
+					return errI2CReadTimeout
 				}
 			}
 
@@ -455,7 +453,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_BTF) {
 				timeout--
 				if timeout == 0 {
-					return errors.New("I2C timeout on read 3 bytes")
+					return errI2CReadTimeout
 				}
 			}
 
@@ -483,7 +481,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			for !i2c.Bus.SR2.HasBits(stm32.I2C_SR2_MSL | stm32.I2C_SR2_BUSY) {
 				timeout--
 				if timeout == 0 {
-					return errors.New("I2C timeout on read clear address")
+					return errI2CWriteTimeout
 				}
 			}
 
@@ -496,8 +494,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 				for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_BTF) {
 					timeout--
 					if timeout == 0 {
-						println("I2C timeout on read 3 bytes")
-						return errors.New("I2C timeout on read 3 bytes")
+						return errI2CReadTimeout
 					}
 				}
 
@@ -510,7 +507,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_BTF) {
 				timeout--
 				if timeout == 0 {
-					return errors.New("I2C timeout on read more than 3 bytes")
+					return errI2CReadTimeout
 				}
 			}
 
@@ -530,7 +527,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 			for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_RxNE) {
 				timeout--
 				if timeout == 0 {
-					return errors.New("I2C timeout on read last byte of more than 3")
+					return errI2CReadTimeout
 				}
 			}
 
@@ -554,7 +551,7 @@ func (i2c I2C) signalStart() error {
 	for i2c.Bus.SR2.HasBits(stm32.I2C_SR2_BUSY) {
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C busy on start")
+			return errI2CSignalStartTimeout
 		}
 	}
 
@@ -569,7 +566,7 @@ func (i2c I2C) signalStart() error {
 	for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_SB) {
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C timeout on start")
+			return errI2CSignalStartTimeout
 		}
 	}
 
@@ -592,8 +589,7 @@ func (i2c I2C) waitForStop() error {
 	for i2c.Bus.SR1.HasBits(stm32.I2C_SR1_STOPF) {
 		timeout--
 		if timeout == 0 {
-			println("I2C timeout on wait for stop signal")
-			return errors.New("I2C timeout on wait for stop signal")
+			return errI2CSignalStopTimeout
 		}
 	}
 
@@ -617,7 +613,7 @@ func (i2c I2C) sendAddress(address uint8, write bool) error {
 		for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_ADDR) {
 			timeout--
 			if timeout == 0 {
-				return errors.New("I2C timeout on send write address")
+				return errI2CWriteTimeout
 			}
 		}
 
@@ -625,7 +621,7 @@ func (i2c I2C) sendAddress(address uint8, write bool) error {
 		for !i2c.Bus.SR2.HasBits(stm32.I2C_SR2_MSL | stm32.I2C_SR2_BUSY | stm32.I2C_SR2_TRA) {
 			timeout--
 			if timeout == 0 {
-				return errors.New("I2C timeout on send write address")
+				return errI2CWriteTimeout
 			}
 		}
 	} else {
@@ -633,7 +629,7 @@ func (i2c I2C) sendAddress(address uint8, write bool) error {
 		for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_ADDR) {
 			timeout--
 			if timeout == 0 {
-				return errors.New("I2C timeout on send read address")
+				return errI2CWriteTimeout
 			}
 		}
 	}
@@ -653,7 +649,7 @@ func (i2c I2C) WriteByte(data byte) error {
 	for !i2c.Bus.SR1.HasBits(stm32.I2C_SR1_TxE) {
 		timeout--
 		if timeout == 0 {
-			return errors.New("I2C timeout on write")
+			return errI2CWriteTimeout
 		}
 	}
 
diff --git a/src/machine/uart.go b/src/machine/uart.go
index bcaefa9d..19febc75 100644
--- a/src/machine/uart.go
+++ b/src/machine/uart.go
@@ -4,6 +4,8 @@ package machine
 
 import "errors"
 
+var errUARTBufferEmpty = errors.New("UART buffer empty")
+
 type UARTConfig struct {
 	BaudRate uint32
 	TX       Pin
@@ -60,7 +62,7 @@ func (uart UART) ReadByte() (byte, error) {
 	// check if RX buffer is empty
 	buf, ok := uart.Buffer.Get()
 	if !ok {
-		return 0, errors.New("Buffer empty")
+		return 0, errUARTBufferEmpty
 	}
 	return buf, nil
 }
diff --git a/src/machine/usb.go b/src/machine/usb.go
index f9efe972..68466e26 100644
--- a/src/machine/usb.go
+++ b/src/machine/usb.go
@@ -9,6 +9,11 @@ import (
 
 const deviceDescriptorSize = 18
 
+var (
+	errUSBCDCBufferEmpty      = errors.New("USB-CDC buffer empty")
+	errUSBCDCWriteByteTimeout = errors.New("USB-CDC write byte timeout")
+)
+
 // DeviceDescriptor implements the USB standard device descriptor.
 //
 // Table 9-8. Standard Device Descriptor
@@ -598,7 +603,7 @@ func (usbcdc USBCDC) ReadByte() (byte, error) {
 	// check if RX buffer is empty
 	buf, ok := usbcdc.Buffer.Get()
 	if !ok {
-		return 0, errors.New("Buffer empty")
+		return 0, errUSBCDCBufferEmpty
 	}
 	return buf, nil
 }