diff --git a/src/machine/board_feather-stm32f405.go b/src/machine/board_feather-stm32f405.go
index 6b7f3023..4eb12f3d 100644
--- a/src/machine/board_feather-stm32f405.go
+++ b/src/machine/board_feather-stm32f405.go
@@ -2,11 +2,6 @@
 
 package machine
 
-import (
-	"device/stm32"
-	"runtime/interrupt"
-)
-
 const (
 	NUM_DIGITAL_IO_PINS = 39
 	NUM_ANALOG_IO_PINS  = 7
@@ -94,34 +89,6 @@ const (
 	UART3_TX_PIN = D15
 )
 
-var (
-	// TBD: why do UART0 and UART1 have different types (struct vs reference)?
-	UART0 = UART{
-		Buffer:          NewRingBuffer(),
-		Bus:             stm32.USART3,
-		AltFuncSelector: stm32.AF7_USART1_2_3,
-	}
-	UART1 = &UART0
-
-//  UART2 = &UART{
-//    Buffer:          NewRingBuffer(),
-//    Bus:             stm32.USART6,
-//    AltFuncSelector: stm32.AF8_USART4_5_6,
-//  }
-//  UART3 = &UART{
-//    Buffer:          NewRingBuffer(),
-//    Bus:             stm32.USART1,
-//    AltFuncSelector: stm32.AF7_USART1_2_3,
-//  }
-)
-
-// set up RX IRQ handler. Follow similar pattern for other UARTx instances
-func init() {
-	UART0.Interrupt = interrupt.New(stm32.IRQ_USART3, UART0.handleInterrupt)
-	//UART2.Interrupt = interrupt.New(stm32.IRQ_USART6, UART2.handleInterrupt)
-	//UART3.Interrupt = interrupt.New(stm32.IRQ_USART1, UART3.handleInterrupt)
-}
-
 // SPI pins
 const (
 	NUM_SPI_INTERFACES = 3
@@ -145,23 +112,3 @@ const (
 	SPI3_SDI_PIN = D18
 	SPI3_SDO_PIN = D19
 )
-
-// Since the first interface is named SPI1, both SPI0 and SPI1 refer to SPI1.
-// TODO: implement SPI2 and SPI3.
-var (
-	// TBD: why do SPI0 and SPI1 have different types (struct vs reference)?
-	SPI0 = SPI{
-		Bus:             stm32.SPI2,
-		AltFuncSelector: stm32.AF5_SPI1_SPI2,
-	}
-	SPI1 = &SPI0
-
-//  SPI2 = &SPI{
-//    Bus:             stm32.SPI3,
-//    AltFuncSelector: stm32.AF6_SPI3,
-//  }
-//  SPI3 = &SPI{
-//    Bus:             stm32.SPI1,
-//    AltFuncSelector: stm32.AF5_SPI1_SPI2,
-//  }
-)
diff --git a/src/machine/machine_stm32f405.go b/src/machine/machine_stm32f405.go
index 0ee80143..9413a977 100644
--- a/src/machine/machine_stm32f405.go
+++ b/src/machine/machine_stm32f405.go
@@ -13,9 +13,8 @@ func CPUFrequency() uint32 {
 	return 168000000
 }
 
-//---------- UART related types and code
+// -- UART ---------------------------------------------------------------------
 
-// UART representation
 type UART struct {
 	Buffer          *RingBuffer
 	Bus             *stm32.USART_Type
@@ -23,81 +22,22 @@ type UART struct {
 	AltFuncSelector stm32.AltFunc
 }
 
-// Configure the UART.
-func (uart UART) configurePins(config UARTConfig) {
-	// enable the alternate functions on the TX and RX pins
-	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.AltFuncSelector)
-	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.AltFuncSelector)
-}
+func (uart UART) configurePins(config UARTConfig)           {}
+func (uart UART) getBaudRateDivisor(baudRate uint32) uint32 { return 0 }
 
-// UART baudrate calc based on the bus and clockspeed
-// NOTE: keep this in sync with the runtime/runtime_stm32f407.go clock init code
-func (uart UART) getBaudRateDivisor(baudRate uint32) uint32 {
-	var clock uint32
-	switch uart.Bus {
-	case stm32.USART1, stm32.USART6:
-		clock = CPUFrequency() / 2 // APB2 Frequency
-	case stm32.USART2, stm32.USART3, stm32.UART4, stm32.UART5:
-		clock = CPUFrequency() / 4 // APB1 Frequency
-	}
-	return clock / baudRate
-}
+// -- SPI ----------------------------------------------------------------------
 
-//---------- SPI related types and code
-
-// SPI on the STM32Fxxx using MODER / alternate function pins
 type SPI struct {
 	Bus             *stm32.SPI_Type
 	AltFuncSelector stm32.AltFunc
 }
 
-// Set baud rate for SPI
-func (spi SPI) getBaudRate(config SPIConfig) uint32 {
-	var conf uint32
+func (spi SPI) configurePins(config SPIConfig)      {}
+func (spi SPI) getBaudRate(config SPIConfig) uint32 { return 0 }
 
-	localFrequency := config.Frequency
-	if spi.Bus != stm32.SPI1 {
-		// Assume it's SPI2 or SPI3 on APB1 at 1/2 the clock frequency of APB2, so
-		//  we want to pretend to request 2x the baudrate asked for
-		localFrequency = localFrequency * 2
-	}
+// -- I2C ----------------------------------------------------------------------
 
-	// set frequency dependent on PCLK prescaler. Since these are rather weird
-	// speeds due to the CPU freqency, pick a range up to that frquency for
-	// clients to use more human-understandable numbers, e.g. nearest 100KHz
-
-	// These are based on APB2 clock frquency (84MHz on the discovery board)
-	// TODO: also include the MCU/APB clock setting in the equation
-	switch true {
-	case localFrequency < 328125:
-		conf = stm32.SPI_PCLK_256
-	case localFrequency < 656250:
-		conf = stm32.SPI_PCLK_128
-	case localFrequency < 1312500:
-		conf = stm32.SPI_PCLK_64
-	case localFrequency < 2625000:
-		conf = stm32.SPI_PCLK_32
-	case localFrequency < 5250000:
-		conf = stm32.SPI_PCLK_16
-	case localFrequency < 10500000:
-		conf = stm32.SPI_PCLK_8
-		// NOTE: many SPI components won't operate reliably (or at all) above 10MHz
-		// Check the datasheet of the part
-	case localFrequency < 21000000:
-		conf = stm32.SPI_PCLK_4
-	case localFrequency < 42000000:
-		conf = stm32.SPI_PCLK_2
-	default:
-		// None of the specific baudrates were selected; choose the lowest speed
-		conf = stm32.SPI_PCLK_256
-	}
-
-	return conf << stm32.SPI_CR1_BR_Pos
-}
-
-// Configure SPI pins for input output and clock
-func (spi SPI) configurePins(config SPIConfig) {
-	config.SCK.ConfigureAltFunc(PinConfig{Mode: PinModeSPICLK}, spi.AltFuncSelector)
-	config.SDO.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDO}, spi.AltFuncSelector)
-	config.SDI.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDI}, spi.AltFuncSelector)
+type I2C struct {
+	Bus             *stm32.I2C_Type
+	AltFuncSelector stm32.AltFunc
 }