Index: firmware/usbstack/usb_serial.c
===================================================================
--- firmware/usbstack/usb_serial.c      (revision 17041)
+++ firmware/usbstack/usb_serial.c      (working copy)
@@ -190,6 +190,16 @@
         case false:
             logf("serial: %s", receive_buffer);
             /* Data received. TODO : Do something with it ? */
+            if(length>=1) {
+                switch(receive_buffer[0]) {
+                    case 'A':
+                        usb_serial_send("Received first letter\n",22);
+                        break;
+                    default:
+                        usb_serial_send("Received another letter\n",24);
+                        break;
+                }
+            }
             usb_drv_recv(usb_endpoint, receive_buffer, sizeof _receive_buffer);
             break;