refactor stm32 UART code

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
+}