Add basic atmega32u support (#3337)

machine/atmega32u: add support for arduino leonardo

src/machine/board_arduino_leonardo.go

@@ -0,0 +1,39 @@
+//go:build arduino_leonardo
+
+package machine
+
+// Return the current CPU frequency in hertz.
+func CPUFrequency() uint32 {
+	return 16000000
+}
+
+// Digital pins, marked as plain numbers on the board.
+const (
+	D0  = PD2 // RX
+	D1  = PD3 // TX
+	D2  = PD1
+	D3  = PD0
+	D4  = PD4
+	D5  = PC6
+	D6  = PD7
+	D7  = PE6
+	D8  = PB4
+	D9  = PB5
+	D10 = PB6
+	D11 = PB7
+	D12 = PD6
+	D13 = PC7
+)
+
+// LED on the Arduino
+const LED Pin = D13
+
+// ADC on the Arduino
+const (
+	ADC0 Pin = PF7
+	ADC1 Pin = PF6
+	ADC2 Pin = PF5
+	ADC3 Pin = PF4
+	ADC4 Pin = PF1
+	ADC5 Pin = PF0
+)