Adding Support for Adafruit Metro M4 Express Airlift (#694)

* machine/metro-m4: add support for Adafruit Metro M4 Express Airlift board

src/machine/board_metro-m4-airlift.go

@@ -0,0 +1,139 @@
+// +build sam,atsamd51,metro_m4_airlift
+
+package machine
+
+import "device/sam"
+
+// used to reset into bootloader
+const RESET_MAGIC_VALUE = 0xf01669ef
+
+// GPIO Pins
+const (
+	D0 = PA23 // UART0 RX/PWM available
+	D1 = PA22 // UART0 TX/PWM available
+	D2 = PB17 // PWM available
+	D3 = PB16 // PWM available
+	D4 = PB13 // PWM available
+	D5 = PB14 // PWM available
+	D6 = PB15 // PWM available
+	D7 = PB12 // PWM available
+
+	D8  = PA21 // PWM available
+	D9  = PA20 // PWM available
+	D10 = PA18 // can be used for PWM or UART1 TX
+	D11 = PA19 // can be used for PWM or UART1 RX
+	D12 = PA17 // PWM available
+	D13 = PA16 // PWM available
+
+	D40 = PB22 // built-in neopixel
+)
+
+// Analog pins
+const (
+	A0 = PA02 // ADC/AIN[0]
+	A1 = PA05 // ADC/AIN[2]
+	A2 = PB06 // ADC/AIN[3]
+	A3 = PB00 // ADC/AIN[4] // NOTE: different between "airlift" and non-airlift versions
+	A4 = PB08 // ADC/AIN[5]
+	A5 = PB09 // ADC/AIN[10]
+)
+
+const (
+	LED = D13
+)
+
+// UART0 aka USBCDC pins
+const (
+	USBCDC_DM_PIN = PA24
+	USBCDC_DP_PIN = PA25
+)
+
+const (
+	UART_TX_PIN = D1
+	UART_RX_PIN = D0
+)
+
+// Note: UART1 is on SERCOM3, defined in machine_atsamd51.go
+
+const (
+	NINA_CS     = PA15
+	NINA_ACK    = PB04
+	NINA_GPIO0  = PB01
+	NINA_RESETN = PB05
+
+	NINA_TX  = PA04
+	NINA_RX  = PA07
+	NINA_RTS = PB23
+)
+
+// UART2 on the Metro M4 Airlift Lite connects to the onboard ESP32-WROOM chip.
+var (
+	UART2 = UART{
+		Buffer: NewRingBuffer(),
+		Bus:    sam.SERCOM0_USART_INT,
+		Mode:   PinSERCOMAlt,
+	}
+)
+
+//go:export SERCOM0_IRQHandler
+func handleUART2() {
+	UART2.Receive(byte((UART2.Bus.DATA.Get() & 0xFF)))
+	UART2.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INT_INTFLAG_RXC)
+}
+
+// I2C pins
+const (
+	SDA_PIN = PB02 // SDA: SERCOM5/PAD[0]
+	SCL_PIN = PB03 // SCL: SERCOM5/PAD[1]
+)
+
+// I2C on the Metro M4.
+var (
+	I2C0 = I2C{Bus: sam.SERCOM5_I2CM,
+		SDA:     SDA_PIN,
+		SCL:     SCL_PIN,
+		PinMode: PinSERCOMAlt}
+)
+
+// SPI pins
+const (
+	SPI0_SCK_PIN  = PA13 // SCK:  SERCOM2/PAD[1]
+	SPI0_MOSI_PIN = PA12 // MOSI: SERCOM2/PAD[0]
+	SPI0_MISO_PIN = PA14 // MISO: SERCOM2/PAD[2]
+)
+
+// SPI on the Metro M4.
+var (
+	SPI0 = SPI{
+		Bus:         sam.SERCOM2_SPIM,
+		SCK:         SPI0_SCK_PIN,
+		MOSI:        SPI0_MOSI_PIN,
+		MISO:        SPI0_MISO_PIN,
+		DOpad:       spiTXPad0SCK1,
+		DIpad:       sercomRXPad2,
+		MISOPinMode: PinSERCOM,
+		MOSIPinMode: PinSERCOM,
+		SCKPinMode:  PinSERCOM,
+	}
+)
+
+const (
+	SPI1_SCK_PIN  = D12 // MISO: SERCOM1/PAD[1]
+	SPI1_MOSI_PIN = D11 // MOSI: SERCOM1/PAD[3]
+	SPI1_MISO_PIN = D13 // SCK:  SERCOM1/PAD[0]
+)
+
+// SPI1 on the Metro M4 on pins 11,12,13
+var (
+	SPI1 = SPI{
+		Bus:         sam.SERCOM1_SPIM,
+		SCK:         SPI1_SCK_PIN,
+		MOSI:        SPI1_MOSI_PIN,
+		MISO:        SPI1_MISO_PIN,
+		DOpad:       spiTXPad3SCK1,
+		DIpad:       sercomRXPad0,
+		MISOPinMode: PinSERCOM,
+		MOSIPinMode: PinSERCOM,
+		SCKPinMode:  PinSERCOM,
+	}
+)

src/machine/machine_atsamd51.go

@@ -509,6 +509,8 @@ func (uart UART) Configure(config UARTConfig) {
 	// determine pads
 	var txpad, rxpad int
 	switch config.TX {
+	case PA04:
+		txpad = sercomTXPad0
 	case PA10:
 		txpad = sercomTXPad2
 	case PA18:
@@ -520,6 +522,8 @@ func (uart UART) Configure(config UARTConfig) {
 	}
 
 	switch config.RX {
+	case PA07:
+		rxpad = sercomRXPad3
 	case PA11:
 		rxpad = sercomRXPad3
 	case PA18: