machine/atmega328pb: refactor to enable extra uart

src/machine/board_atmega328pb.go

@@ -0,0 +1,51 @@
+//go:build avr && atmega328pb
+
+package machine
+
+// Return the current CPU frequency in hertz.
+func CPUFrequency() uint32 {
+	return 16000000
+}
+
+const (
+	// Note: start at port B because there is no port A.
+	portB Pin = iota * 8
+	portC
+	portD
+	portE
+)
+
+const (
+	PB0 = portB + 0
+	PB1 = portB + 1 // peripherals: Timer1 channel A
+	PB2 = portB + 2 // peripherals: Timer1 channel B
+	PB3 = portB + 3 // peripherals: Timer2 channel A
+	PB4 = portB + 4
+	PB5 = portB + 5
+	PB6 = portB + 6
+	PB7 = portB + 7
+	PC0 = portC + 0
+	PC1 = portC + 1
+	PC2 = portC + 2
+	PC3 = portC + 3
+	PC4 = portC + 4
+	PC5 = portC + 5
+	PC6 = portC + 6
+	PC7 = portC + 7
+	PD0 = portD + 0
+	PD1 = portD + 1
+	PD2 = portD + 2
+	PD3 = portD + 3 // peripherals: Timer2 channel B
+	PD4 = portD + 4
+	PD5 = portD + 5 // peripherals: Timer0 channel B
+	PD6 = portD + 6 // peripherals: Timer0 channel A
+	PD7 = portD + 7
+	PE0 = portE + 0
+	PE1 = portE + 1
+	PE2 = portE + 2
+	PE3 = portE + 3
+	PE4 = portE + 4
+	PE5 = portE + 5
+	PE6 = portE + 6
+	PE7 = portE + 7
+)