refactor stm32 UART code

src/machine/board_stm32f4disco.go

@@ -2,6 +2,11 @@
 
 package machine
 
+import (
+	"device/stm32"
+	"runtime/interrupt"
+)
+
 const (
 	PA0  = portA + 0
 	PA1  = portA + 1
@@ -110,3 +115,17 @@ const (
 	UART_TX_PIN = PA2
 	UART_RX_PIN = PA3
 )
+
+var (
+	UART0 = UART{
+		Buffer:          NewRingBuffer(),
+		Bus:             stm32.USART2,
+		AltFuncSelector: stm32.AF7_USART1_2_3,
+	}
+	UART1 = &UART0
+)
+
+// set up RX IRQ handler. Follow similar pattern for other UARTx instances
+func init() {
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, UART0.handleInterrupt)
+}

src/machine/machine_stm32_moder_gpio.go

@@ -82,7 +82,7 @@ func (p Pin) ConfigureAltFunc(config PinConfig, altFunc stm32.AltFunc) {
 		port.PUPDR.ReplaceBits(stm32.GPIOPUPDRFloating, 0x3, pos)
 		p.SetAltFunc(altFunc)
 
-	// I2C)
+	// I2C
 	case PinModeI2CSCL:
 		port.MODER.ReplaceBits(stm32.GPIOModeOutputAltFunc, 0x3, pos)
 		port.OTYPER.ReplaceBits(stm32.GPIOOutputTypeOpenDrain, 0x1, pos)

src/machine/machine_stm32_uart.go

@@ -0,0 +1,62 @@
+// +build stm32
+
+package machine
+
+// Peripheral abstraction layer for UARTs on the stm32 family.
+
+import (
+	"device/stm32"
+	"runtime/interrupt"
+	"unsafe"
+)
+
+// Configure the UART.
+func (uart UART) Configure(config UARTConfig) {
+	// Default baud rate to 115200.
+	if config.BaudRate == 0 {
+		config.BaudRate = 115200
+	}
+
+	// Set the GPIO pins to defaults if they're not set
+	if config.TX == 0 && config.RX == 0 {
+		config.TX = UART_TX_PIN
+		config.RX = UART_RX_PIN
+	}
+
+	// Enable USART clock
+	enableAltFuncClock(unsafe.Pointer(uart.Bus))
+
+	uart.configurePins(config)
+
+	// Set baud rate
+	uart.SetBaudRate(config.BaudRate)
+
+	// Enable USART port, tx, rx and rx interrupts
+	uart.Bus.CR1.Set(stm32.USART_CR1_TE | stm32.USART_CR1_RE | stm32.USART_CR1_RXNEIE | stm32.USART_CR1_UE)
+
+	// Enable RX IRQ
+	uart.Interrupt.SetPriority(0xc0)
+	uart.Interrupt.Enable()
+}
+
+// handleInterrupt should be called from the appropriate interrupt handler for
+// this UART instance.
+func (uart *UART) handleInterrupt(interrupt.Interrupt) {
+	uart.Receive(byte((uart.Bus.DR.Get() & 0xFF)))
+}
+
+// SetBaudRate sets the communication speed for the UART. Defer to chip-specific
+// routines for calculation
+func (uart UART) SetBaudRate(br uint32) {
+	divider := uart.getBaudRateDivisor(br)
+	uart.Bus.BRR.Set(divider)
+}
+
+// WriteByte writes a byte of data to the UART.
+func (uart UART) WriteByte(c byte) error {
+	uart.Bus.DR.Set(uint32(c))
+
+	for !uart.Bus.SR.HasBits(stm32.USART_SR_TXE) {
+	}
+	return nil
+}

src/machine/machine_stm32f103xx.go

@@ -104,25 +104,17 @@ func enableAltFuncClock(bus unsafe.Pointer) {
 	}
 }
 
-// UART
+//---------- UART related types and code
+
+// UART representation
 type UART struct {
 	Buffer    *RingBuffer
 	Bus       *stm32.USART_Type
 	Interrupt interrupt.Interrupt
 }
 
-// Configure the UART.
+// Configure the TX and RX pins
-func (uart UART) Configure(config UARTConfig) {
+func (uart UART) configurePins(config UARTConfig) {
-	// Default baud rate to 115200.
-	if config.BaudRate == 0 {
-		config.BaudRate = 115200
-	}
-
-	// Set the GPIO pins to defaults if they're not set
-	if config.TX == 0 && config.RX == 0 {
-		config.TX = UART_TX_PIN
-		config.RX = UART_RX_PIN
-	}
 
 	// pins
 	switch config.TX {
@@ -139,23 +131,11 @@ func (uart UART) Configure(config UARTConfig) {
 	}
 	config.TX.Configure(PinConfig{Mode: PinOutput50MHz + PinOutputModeAltPushPull})
 	config.RX.Configure(PinConfig{Mode: PinInputModeFloating})
-
-	// Enable USART clock
-	enableAltFuncClock(unsafe.Pointer(uart.Bus))
-
-	// Set baud rate
-	uart.SetBaudRate(config.BaudRate)
-
-	// Enable USART port
-	uart.Bus.CR1.Set(stm32.USART_CR1_TE | stm32.USART_CR1_RE | stm32.USART_CR1_RXNEIE | stm32.USART_CR1_UE)
-
-	// Enable RX IRQ
-	uart.Interrupt.SetPriority(0xc0)
-	uart.Interrupt.Enable()
 }
 
-// SetBaudRate sets the communication speed for the UART.
+// Determine the divisor for USARTs to get the given baudrate
-func (uart UART) SetBaudRate(br uint32) {
+func (uart UART) getBaudRateDivisor(br uint32) uint32 {
+
 	// Note: PCLK2 (from APB2) used for USART1 and PCLK1 for USART2, 3, 4, 5
 	var divider uint32
 	if uart.Bus == stm32.USART1 {
@@ -165,22 +145,7 @@ func (uart UART) SetBaudRate(br uint32) {
 		// first divide by PCLK1 prescaler (div 2) and then desired baudrate
 		divider = CPUFrequency() / 2 / br
 	}
-	uart.Bus.BRR.Set(divider)
+	return divider
-}
-
-// WriteByte writes a byte of data to the UART.
-func (uart UART) WriteByte(c byte) error {
-	uart.Bus.DR.Set(uint32(c))
-
-	for !uart.Bus.SR.HasBits(stm32.USART_SR_TXE) {
-	}
-	return nil
-}
-
-// handleInterrupt should be called from the appropriate interrupt handler for
-// this UART instance.
-func (uart *UART) handleInterrupt(interrupt.Interrupt) {
-	uart.Receive(byte((uart.Bus.DR.Get() & 0xFF)))
 }
 
 // SPI on the STM32.

src/machine/machine_stm32f407.go

@@ -79,75 +79,32 @@ func enableAltFuncClock(bus unsafe.Pointer) {
 	}
 }
 
-// UART
+//---------- UART related types and code
+
+// UART representation
 type UART struct {
 	Buffer          *RingBuffer
 	Bus             *stm32.USART_Type
+	Interrupt       interrupt.Interrupt
 	AltFuncSelector stm32.AltFunc
 }
 
-var (
-	UART0 = UART{
-		Buffer:          NewRingBuffer(),
-		Bus:             stm32.USART2,
-		AltFuncSelector: stm32.AF7_USART1_2_3,
-	}
-	UART1 = &UART0
-)
-
 // Configure the UART.
-func (uart UART) Configure(config UARTConfig) {
+func (uart UART) configurePins(config UARTConfig) {
-	// Default baud rate to 115200.
+	// enable the alternate functions on the TX and RX pins
-	if config.BaudRate == 0 {
-		config.BaudRate = 115200
-	}
-
-	// Set the GPIO pins to defaults if they're not set
-	if config.TX == 0 && config.RX == 0 {
-		config.TX = UART_TX_PIN
-		config.RX = UART_RX_PIN
-	}
-
-	// Enable USART clock
-	enableAltFuncClock(unsafe.Pointer(uart.Bus))
-
-	// use standard TX/RX pins PA2 and PA3
 	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.AltFuncSelector)
 	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.AltFuncSelector)
-
-	/*
-	  Set baud rate(115200)
-	  OVER8 = 0, APB1 = 42mhz
-	  +----------+--------+
-	  | baudrate | BRR    |
-	  +----------+--------+
-	  | 1200     | 0x88B8 |
-	  | 2400     | 0x445C |
-	  | 9600     | 0x1117 |
-	  | 19200    | 0x88C  |
-	  | 38400    | 0x446  |
-	  | 57600    | 0x2D9  |
-	  | 115200   | 0x16D  |
-	  +----------+--------+
-	*/
-	uart.Bus.BRR.Set(0x16c)
-
-	// Enable USART2 port.
-	uart.Bus.CR1.Set(stm32.USART_CR1_TE | stm32.USART_CR1_RE | stm32.USART_CR1_RXNEIE | stm32.USART_CR1_UE)
-
-	// Enable RX IRQ. TODO: pick the right IRQ_xxx for the bus and the uart
-	intr := interrupt.New(stm32.IRQ_USART2, func(interrupt.Interrupt) {
-		UART1.Receive(byte((UART1.Bus.DR.Get() & 0xFF)))
-	})
-	intr.SetPriority(0xc0)
-	intr.Enable()
 }
 
-// WriteByte writes a byte of data to the UART.
+// UART baudrate calc based on the bus and clockspeed
-func (uart UART) WriteByte(c byte) error {
+// NOTE: keep this in sync with the runtime/runtime_stm32f407.go clock init code
-	uart.Bus.DR.Set(uint32(c))
+func (uart UART) getBaudRateDivisor(baudRate uint32) uint32 {
-
+	var clock uint32
-	for !uart.Bus.SR.HasBits(stm32.USART_SR_TXE) {
+	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 nil
+	return clock / baudRate
 }