1 files changed, 33 insertions, 2 deletions

diff --git a/hw/usb.h b/hw/usb.h
index 4a009a5848..55b7e5850a 100644
--- a/hw/usb.h
+++ b/hw/usb.h
@@ -120,18 +120,49 @@ typedef struct USBPacket USBPacket;
 /* definition of a USB device */
 struct USBDevice {
     void *opaque;
+
+    /* 
+     * Process USB packet. 
+     * Called by the HC (Host Controller).
+     *
+     * Returns length of the transaction 
+     * or one of the USB_RET_XXX codes.
+     */ 
     int (*handle_packet)(USBDevice *dev, USBPacket *p);
+
+    /* 
+     * Called when device is destroyed.
+     */
     void (*handle_destroy)(USBDevice *dev);
 
     int speed;
 
     /* The following fields are used by the generic USB device
-       layer. They are here just to avoid creating a new structure for
-       them. */
+       layer. They are here just to avoid creating a new structure 
+       for them. */
+
+    /*
+     * Reset the device
+     */  
     void (*handle_reset)(USBDevice *dev);
+
+    /*
+     * Process control request.
+     * Called from handle_packet().
+     *
+     * Returns length or one of the USB_RET_ codes.
+     */
     int (*handle_control)(USBDevice *dev, int request, int value,
                           int index, int length, uint8_t *data);
+
+    /*
+     * Process data transfers (both BULK and ISOC).
+     * Called from handle_packet().
+     *
+     * Returns length or one of the USB_RET_ codes.
+     */
     int (*handle_data)(USBDevice *dev, USBPacket *p);
+
     uint8_t addr;
     char devname[32];