diff -ur dev/usb/ugen.c /usr/local/src/mykernelhack/dev/usb/ugen.c
--- dev/usb/ugen.c	Thu Feb 21 05:30:12 2002
+++ /usr/local/src/mykernelhack/dev/usb/ugen.c	Sat Jan  3 21:05:36 2004
@@ -107,6 +107,7 @@
 		void *dmabuf;
 		u_int16_t sizes[UGEN_NISORFRMS];
 	} isoreqs[UGEN_NISOREQS];
+	int chksum;		/* apply checksum to raw packet (isoc) */
 };
 
 struct ugen_softc {
@@ -119,6 +120,7 @@
 #define IN  1
 
 	int sc_refcnt;
+	int sc_chksum;		/* checksum setting (for isoc endpoints) */
 	u_char sc_dying;
 };
 
@@ -394,6 +396,7 @@
 				free(sce->ibuf, M_USBDEV);
 				return (EIO);
 			}
+			sce->chksum = sc->sc_chksum;
 			for(i = 0; i < UGEN_NISOREQS; ++i) {
 				sce->isoreqs[i].sce = sce;
 				xfer = usbd_alloc_xfer(sc->sc_udev);
@@ -867,6 +870,32 @@
 		u_int32_t actlen = req->sizes[i];
 		char const *buf = (char const *)req->dmabuf + isize * i;
 
+		/* checksum */
+		if ( sce->chksum > 0 ) {
+			if ( actlen > 2 ) {
+				int j;
+				u_int32_t checksum, packetsum;
+				unsigned char const *cbuf;
+				cbuf = (unsigned char const *)req->dmabuf + isize * i;
+				packetsum = 0;
+				for (j = 0; j < actlen-2; ++j) {
+					packetsum += cbuf[j];
+				}
+				checksum = cbuf[j] + cbuf[j+1]*256u;
+				if ( (packetsum&0xffff) == checksum ) {
+					DPRINTFN(4, ("ugen_isoc_rintr: checksum OK\n"));
+					actlen -= 2;
+				} else {
+					DPRINTFN(4, ("ugen_isoc_rintr: checksum NG %x %x\n",packetsum,checksum));
+					actlen = 0;
+				}
+			} else {
+				if ( actlen > 0 ) 
+					DPRINTFN(4, ("ugen_isoc_rintr: ignore short data %d\n",actlen));
+				actlen = 0;
+			}
+		}
+
 		/* copy data to buffer */
 		while (actlen > 0) {
 			n = min(actlen, sce->limit - sce->fill);
@@ -1042,6 +1071,13 @@
 			)
 			return (EINVAL);
 		sce->timeout = *(int *)addr;
+		return (0);
+	case USB_SET_PACKETCHKSUM:
+		if (endpt != USB_CONTROL_ENDPOINT)
+			return (EINVAL);
+		if ( (*(int *)addr > 1) || (*(int *)addr < 0) )
+			return (EINVAL);
+		sc->sc_chksum = *(int *)addr;
 		return (0);
 	default:
 		break;
diff -ur dev/usb/usb.h /usr/local/src/mykernelhack/dev/usb/usb.h
--- dev/usb/usb.h	Tue Feb 26 19:27:49 2002
+++ /usr/local/src/mykernelhack/dev/usb/usb.h	Fri Jan  2 12:09:26 2004
@@ -667,6 +667,7 @@
 #define USB_GET_DEVICEINFO	_IOR ('U', 112, struct usb_device_info)
 #define USB_SET_SHORT_XFER	_IOW ('U', 113, int)
 #define USB_SET_TIMEOUT		_IOW ('U', 114, int)
+#define USB_SET_PACKETCHKSUM	_IOW ('U', 115, int)
 
 /* Modem device */
 #define USB_GET_CM_OVER_DATA	_IOR ('U', 130, int)