esp8266: provide hardware pin constants like GPIO2

src/machine/board_nodemcu.go

@@ -7,15 +7,15 @@ package machine
 
 // GPIO pins on the NodeMCU board.
 const (
-	D0 Pin = 16
-	D1 Pin = 5
-	D2 Pin = 4
-	D3 Pin = 0
-	D4 Pin = 2
-	D5 Pin = 14
-	D6 Pin = 12
-	D7 Pin = 13
-	D8 Pin = 15
+	D0 = GPIO16
+	D1 = GPIO5
+	D2 = GPIO4
+	D3 = GPIO0
+	D4 = GPIO2
+	D5 = GPIO14
+	D6 = GPIO12
+	D7 = GPIO13
+	D8 = GPIO15
 )
 
 // Onboard blue LED (on the AI-Thinker module).

src/machine/machine_esp8266.go

@@ -19,6 +19,27 @@ const (
 	PinInput
 )
 
+// Hardware pin numbers
+const (
+	GPIO0 Pin = iota
+	GPIO1
+	GPIO2
+	GPIO3
+	GPIO4
+	GPIO5
+	GPIO6
+	GPIO7
+	GPIO8
+	GPIO9
+	GPIO10
+	GPIO11
+	GPIO12
+	GPIO13
+	GPIO14
+	GPIO15
+	GPIO16
+)
+
 // Pins that are fixed by the chip.
 const (
 	UART_TX_PIN Pin = 1