all: add Arduino Nano support

Makefile

@@ -265,6 +265,8 @@ smoketest:
 ifneq ($(AVR), 0)
 	$(TINYGO) build -size short -o test.hex -target=arduino             examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=arduino-nano        examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=digispark           examples/blinky1
 	@$(MD5SUM) test.hex
 endif

src/machine/board_arduino_nano.go

@@ -0,0 +1,27 @@
+// +build arduino_nano
+
+package machine
+
+// Return the current CPU frequency in hertz.
+func CPUFrequency() uint32 {
+	return 16000000
+}
+
+// LED on the Arduino
+const LED Pin = 13
+
+// ADC on the Arduino
+const (
+	ADC0 Pin = 0
+	ADC1 Pin = 1
+	ADC2 Pin = 2
+	ADC3 Pin = 3
+	ADC4 Pin = 4 // Used by TWI for SDA
+	ADC5 Pin = 5 // Used by TWI for SCL
+)
+
+// UART pins
+const (
+	UART_TX_PIN Pin = 1
+	UART_RX_PIN Pin = 0
+)

targets/arduino-nano.json

@@ -0,0 +1,9 @@
+{
+	"inherits": ["atmega328p"],
+	"build-tags": ["arduino_nano"],
+	"ldflags": [
+		"-Wl,--defsym=_bootloader_size=512",
+		"-Wl,--defsym=_stack_size=512"
+	],
+	"flash-command": "avrdude -c arduino -p atmega328p -b 57600 -P {port} -U flash:w:{hex}:i"
+}

targets/arduino.json

@@ -1,19 +1,9 @@
 {
-	"inherits": ["avr"],
-	"llvm-target": "avr-atmel-none",
-	"cpu": "atmega328p",
-	"build-tags": ["arduino", "atmega328p", "atmega", "avr5"],
-	"cflags": [
-		"-mmcu=atmega328p"
-	],
+	"inherits": ["atmega328p"],
+	"build-tags": ["arduino"],
 	"ldflags": [
 		"-Wl,--defsym=_bootloader_size=512",
 		"-Wl,--defsym=_stack_size=512"
 	],
-	"linkerscript": "src/device/avr/atmega328p.ld",
-	"extra-files": [
-		"targets/avr.S",
-		"src/device/avr/atmega328p.s"
-	],
 	"flash-command": "avrdude -c arduino -p atmega328p -P {port} -U flash:w:{hex}:i"
 }

targets/atmega328p.json

@@ -0,0 +1,14 @@
+{
+	"inherits": ["avr"],
+	"llvm-target": "avr-atmel-none",
+	"cpu": "atmega328p",
+	"build-tags": ["atmega328p", "atmega", "avr5"],
+	"cflags": [
+		"-mmcu=atmega328p"
+	],
+	"linkerscript": "src/device/avr/atmega328p.ld",
+	"extra-files": [
+		"targets/avr.S",
+		"src/device/avr/atmega328p.s"
+	]
+}