Adds USB serial number support for sketches to Arduino 1.5.8. See http://forum.pololu.com/viewtopic.php?f=10&t=9312&p=42202#p42202

arduino_1.5.8_serial_number.patch

--- hardware/arduino/avr/cores/arduino/USBCore.cpp	Fri Nov  7 10:14:04 2014
+++ hardware/arduino/avr/cores/arduino/USBCore.cpp	Tue Dec  9 11:09:30 2014
@@ -18,6 +18,8 @@
 
 #include "USBAPI.h"
 
+#include <avr/boot.h>
+
 #if defined(USBCON)
 
 #define EP_TYPE_CONTROL				0x00
@@ -80,10 +81,10 @@
 
 //	DEVICE DESCRIPTOR
 const DeviceDescriptor USB_DeviceDescriptor =
-	D_DEVICE(0x00,0x00,0x00,64,USB_VID,USB_PID,0x100,IMANUFACTURER,IPRODUCT,0,1);
+	D_DEVICE(0x00,0x00,0x00,64,USB_VID,USB_PID,0x100,IMANUFACTURER,IPRODUCT,ISERIAL,1);
 
 const DeviceDescriptor USB_DeviceDescriptorA =
-	D_DEVICE(DEVICE_CLASS,0x00,0x00,64,USB_VID,USB_PID,0x100,IMANUFACTURER,IPRODUCT,0,1);
+	D_DEVICE(DEVICE_CLASS,0x00,0x00,64,USB_VID,USB_PID,0x100,IMANUFACTURER,IPRODUCT,ISERIAL,1);
 
 //==================================================================
 //==================================================================
@@ -432,6 +433,28 @@
         return true;
 }
 
+static char nibbleToHex(uint8_t n)
+{
+    if (n <= 9) { return '0' + n; }
+    else { return 'a' + (n - 10); }
+}
+
+static bool USB_SendSerialNumber() {
+    SendControl(2 + 20 * 2);
+    SendControl(3);
+    for(uint8_t i = 14; i < 24; i++) {
+        uint8_t b = boot_signature_byte_get(i);
+        if (!(SendControl(nibbleToHex(b >> 4)) &&
+            SendControl(0) &&
+            SendControl(nibbleToHex(b & 0xF)) &&
+            SendControl(0)))
+        {
+            return false;
+        }
+    }
+    return true;
+}
+
 //	Does not timeout or cross fifo boundaries
 //	Will only work for transfers <= 64 bytes
 //	TODO
@@ -509,6 +532,9 @@
 		}
 		else if (setup.wValueL == IMANUFACTURER) {
 			return USB_SendStringDescriptor(STRING_MANUFACTURER, strlen(USB_MANUFACTURER));
+		}
+		else if (setup.wValueL == ISERIAL) {
+			return USB_SendSerialNumber();
 		}
 		else
 			return false;
     
--- hardware/arduino/avr/cores/arduino/USBDesc.h	Fri Nov  7 10:14:04 2014
+++ hardware/arduino/avr/cores/arduino/USBDesc.h	Tue Dec  9 10:49:24 2014
@@ -61,3 +61,4 @@
 #define IMANUFACTURER	1
 #define IPRODUCT		2
 
+#define ISERIAL 3