atmega2560: support UART1-3

+ example for uart

src/examples/uart/uart.go

@@ -0,0 +1,25 @@
+// This reads from UART1 and outputs to default serial, usually UART0 or USB.
+// Example of how to work with UARTs other than the default.
+package main
+
+import (
+	"machine"
+	"time"
+)
+
+var (
+	uart = machine.UART1
+	tx   = machine.UART1_TX_PIN
+	rx   = machine.UART1_RX_PIN
+)
+
+func main() {
+	uart.Configure(machine.UARTConfig{TX: tx, RX: rx})
+	for {
+		if uart.Buffered() > 0 {
+			data, _ := uart.ReadByte()
+			print(string(data))
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+}

src/machine/board_arduino_mega2560.go

@@ -3,6 +3,11 @@
 
 package machine
 
+import (
+	"device/avr"
+	"runtime/interrupt"
+)
+
 // Return the current CPU frequency in hertz.
 func CPUFrequency() uint32 {
 	return 16000000
@@ -62,12 +67,12 @@ const (
 	D11 Pin = PB5
 	D12 Pin = PB6
 	D13 Pin = PB7
-	D14 Pin = PJ1
-	D15 Pin = PJ0
-	D16 Pin = PH1
-	D17 Pin = PH0
-	D18 Pin = PD3
-	D19 Pin = PD2
+	D14 Pin = PJ1 // TX3
+	D15 Pin = PJ0 // RX3
+	D16 Pin = PH1 // TX2
+	D17 Pin = PH0 // RX2
+	D18 Pin = PD3 // TX1
+	D19 Pin = PD2 // RX1
 	D20 Pin = PD1
 	D21 Pin = PD0
 	D22 Pin = PA0
@@ -103,3 +108,59 @@ const (
 	D52 Pin = PB1
 	D53 Pin = PB0
 )
+
+// UART pins
+const (
+	UART_TX_PIN  Pin = UART0_TX_PIN
+	UART_RX_PIN  Pin = UART0_RX_PIN
+	UART0_TX_PIN Pin = D1
+	UART0_RX_PIN Pin = D0
+	UART1_TX_PIN Pin = D18
+	UART1_RX_PIN Pin = D19
+	UART2_TX_PIN Pin = D16
+	UART2_RX_PIN Pin = D17
+	UART3_TX_PIN Pin = D14
+	UART3_RX_PIN Pin = D15
+)
+
+var (
+	UART1  = &_UART1
+	_UART1 = UART{
+		Buffer: NewRingBuffer(),
+
+		dataReg:    avr.UDR1,
+		baudRegH:   avr.UBRR1H,
+		baudRegL:   avr.UBRR1L,
+		statusRegA: avr.UCSR1A,
+		statusRegB: avr.UCSR1B,
+		statusRegC: avr.UCSR1C,
+	}
+	UART2  = &_UART2
+	_UART2 = UART{
+		Buffer: NewRingBuffer(),
+
+		dataReg:    avr.UDR2,
+		baudRegH:   avr.UBRR2H,
+		baudRegL:   avr.UBRR2L,
+		statusRegA: avr.UCSR2A,
+		statusRegB: avr.UCSR2B,
+		statusRegC: avr.UCSR2C,
+	}
+	UART3  = &_UART3
+	_UART3 = UART{
+		Buffer: NewRingBuffer(),
+
+		dataReg:    avr.UDR3,
+		baudRegH:   avr.UBRR3H,
+		baudRegL:   avr.UBRR3L,
+		statusRegA: avr.UCSR3A,
+		statusRegB: avr.UCSR3B,
+		statusRegC: avr.UCSR3C,
+	}
+)
+
+func init() {
+	interrupt.New(irq_USART1_RX, _UART1.handleInterrupt)
+	interrupt.New(irq_USART2_RX, _UART2.handleInterrupt)
+	interrupt.New(irq_USART3_RX, _UART3.handleInterrupt)
+}

src/machine/machine_atmega.go

@@ -129,12 +129,34 @@ var DefaultUART = UART0
 var (
 	// UART0 is the hardware serial port on the AVR.
 	UART0  = &_UART0
-	_UART0 = UART{Buffer: NewRingBuffer()}
+	_UART0 = UART{
+		Buffer: NewRingBuffer(),
+
+		dataReg:    avr.UDR0,
+		baudRegH:   avr.UBRR0H,
+		baudRegL:   avr.UBRR0L,
+		statusRegA: avr.UCSR0A,
+		statusRegB: avr.UCSR0B,
+		statusRegC: avr.UCSR0C,
+	}
 )
 
+func init() {
+	// Register the UART interrupt.
+	interrupt.New(irq_USART0_RX, _UART0.handleInterrupt)
+}
+
 // UART on the AVR.
 type UART struct {
 	Buffer *RingBuffer
+
+	dataReg  *volatile.Register8
+	baudRegH *volatile.Register8
+	baudRegL *volatile.Register8
+
+	statusRegA *volatile.Register8
+	statusRegB *volatile.Register8
+	statusRegC *volatile.Register8
 }
 
 // Configure the UART on the AVR. Defaults to 9600 baud on Arduino.
@@ -143,38 +165,37 @@ func (uart *UART) Configure(config UARTConfig) {
 		config.BaudRate = 9600
 	}
 
-	// Register the UART interrupt.
-	interrupt.New(irq_USART0_RX, func(intr interrupt.Interrupt) {
-		// Read register to clear it.
-		data := avr.UDR0.Get()
-
-		// Ensure no error.
-		if !avr.UCSR0A.HasBits(avr.UCSR0A_FE0 | avr.UCSR0A_DOR0 | avr.UCSR0A_UPE0) {
-			// Put data from UDR register into buffer.
-			UART0.Receive(byte(data))
-		}
-	})
-
 	// Set baud rate based on prescale formula from
 	// https://www.microchip.com/webdoc/AVRLibcReferenceManual/FAQ_1faq_wrong_baud_rate.html
 	// ((F_CPU + UART_BAUD_RATE * 8L) / (UART_BAUD_RATE * 16L) - 1)
 	ps := ((CPUFrequency()+config.BaudRate*8)/(config.BaudRate*16) - 1)
-	avr.UBRR0H.Set(uint8(ps >> 8))
-	avr.UBRR0L.Set(uint8(ps & 0xff))
+	uart.baudRegH.Set(uint8(ps >> 8))
+	uart.baudRegL.Set(uint8(ps & 0xff))
 
 	// enable RX, TX and RX interrupt
-	avr.UCSR0B.Set(avr.UCSR0B_RXEN0 | avr.UCSR0B_TXEN0 | avr.UCSR0B_RXCIE0)
+	uart.statusRegB.Set(avr.UCSR0B_RXEN0 | avr.UCSR0B_TXEN0 | avr.UCSR0B_RXCIE0)
 
 	// 8-bits data
-	avr.UCSR0C.Set(avr.UCSR0C_UCSZ01 | avr.UCSR0C_UCSZ00)
+	uart.statusRegC.Set(avr.UCSR0C_UCSZ01 | avr.UCSR0C_UCSZ00)
+}
+
+func (uart *UART) handleInterrupt(intr interrupt.Interrupt) {
+	// Read register to clear it.
+	data := uart.dataReg.Get()
+
+	// Ensure no error.
+	if !uart.statusRegA.HasBits(avr.UCSR0A_FE0 | avr.UCSR0A_DOR0 | avr.UCSR0A_UPE0) {
+		// Put data from UDR register into buffer.
+		uart.Receive(byte(data))
+	}
 }
 
 // WriteByte writes a byte of data to the UART.
 func (uart *UART) WriteByte(c byte) error {
 	// Wait until UART buffer is not busy.
-	for !avr.UCSR0A.HasBits(avr.UCSR0A_UDRE0) {
+	for !uart.statusRegA.HasBits(avr.UCSR0A_UDRE0) {
 	}
-	avr.UDR0.Set(c) // send char
+	uart.dataReg.Set(c) // send char
 	return nil
 }
 

src/machine/machine_atmega2560.go

@@ -9,6 +9,9 @@ import (
 )
 
 const irq_USART0_RX = avr.IRQ_USART0_RX
+const irq_USART1_RX = avr.IRQ_USART1_RX
+const irq_USART2_RX = avr.IRQ_USART2_RX
+const irq_USART3_RX = avr.IRQ_USART3_RX
 
 const (
 	portA Pin = iota * 8