Merge branch 'usb' into v1

doc.go

@@ -79,7 +79,35 @@ serial port:
 		fmt.Printf("%v", string(buff[:n]))
 	}
 
-This library doesn't make use of cgo and "C" package, so it's a pure go library
-that can be easily cross compiled.
+If a port is a virtual USB-CDC serial port (for example an USB-to-RS232
+cable or a microcontroller development board) is possible to retrieve
+the USB metadata, like VID/PID or USB Serial Number, with the
+GetDetailedPortsList function in the enumerator package:
+
+	import "go.bug.st/serial.v1/enumerator"
+
+	ports, err := enumerator.GetDetailedPortsList()
+	if err != nil {
+		log.Fatal(err)
+	}
+	if len(ports) == 0 {
+		fmt.Println("No serial ports found!")
+		return
+	}
+	for _, port := range ports {
+		fmt.Printf("Found port: %s\n", port.Name)
+		if port.IsUSB {
+			fmt.Printf("   USB ID     %s:%s\n", port.VID, port.PID)
+			fmt.Printf("   USB serial %s\n", port.SerialNumber)
+		}
+	}
+
+for details on USB port enumeration see the documentation of the specific package.
+
+This library tries to avoid the use of the "C" package (and consequently the need
+of cgo) to simplify cross compiling.
+Unfortunately the USB enumeration package for darwin (MacOSX) requires cgo
+to access the IOKit framework. This means that if you need USB enumeration
+on darwin you're forced to use cgo.
 */
 package serial // import "go.bug.st/serial.v1"