diff --git a/devicemodel/hw/pci/xhci.c b/devicemodel/hw/pci/xhci.c
index 9df331b53..0099166df 100644
--- a/devicemodel/hw/pci/xhci.c
+++ b/devicemodel/hw/pci/xhci.c
@@ -2161,8 +2161,6 @@ pci_xhci_xfer_complete(struct pci_xhci_vdev *xdev,
 		       uint32_t epid,
 		       int *do_intr)
 {
-	struct pci_xhci_dev_emu *dev;
-	struct pci_xhci_dev_ep	*devep;
 	struct xhci_dev_ctx	*dev_ctx;
 	struct xhci_endp_ctx	*ep_ctx;
 	struct xhci_trb		*trb;
@@ -2172,8 +2170,6 @@ pci_xhci_xfer_complete(struct pci_xhci_vdev *xdev,
 	uint32_t i;
 	int  err = XHCI_TRB_ERROR_SUCCESS;
 
-	dev = XHCI_SLOTDEV_PTR(xdev, slot);
-	devep = &dev->eps[epid];
 	dev_ctx = pci_xhci_get_dev_ctx(xdev, slot);
 
 	assert(dev_ctx != NULL);
@@ -2219,22 +2215,18 @@ pci_xhci_xfer_complete(struct pci_xhci_vdev *xdev,
 			 trbflags, err,
 			 trb->dwTrb3 & XHCI_TRB_3_IOC_BIT ? 1 : 0);
 
-		if (!xfer->data[i].processed) {
+		if (xfer->data[i].processed < USB_XFER_BLK_HANDLED) {
 			xfer->head = (int)i;
 			break;
 		}
 
+		xfer->data[i].processed = USB_XFER_BLK_FREE;
 		xfer->ndata--;
 		xfer->head = (xfer->head + 1) % USB_MAX_XFER_BLOCKS;
 		edtla += xfer->data[i].bdone;
 
 		trb->dwTrb3 = (trb->dwTrb3 & ~0x1) | (xfer->data[i].ccs);
 
-		pci_xhci_update_ep_ring(xdev, dev, devep, ep_ctx,
-					xfer->data[i].streamid,
-					xfer->data[i].trbnext,
-					xfer->data[i].ccs);
-
 		/* Only interrupt if IOC or short packet */
 		if (!(trb->dwTrb3 & XHCI_TRB_3_IOC_BIT) &&
 		    !((err == XHCI_TRB_ERROR_SHORT_PKT) &&
@@ -2415,7 +2407,7 @@ retry:
 				err = XHCI_TRB_ERROR_STALL;
 				goto errout;
 			}
-			xfer_block->processed = 1;
+			xfer_block->processed = USB_XFER_BLK_FREE;
 			break;
 
 		case XHCI_TRB_TYPE_SETUP_STAGE:
@@ -2446,7 +2438,7 @@ retry:
 				err = XHCI_TRB_ERROR_STALL;
 				goto errout;
 			}
-			xfer_block->processed = 1;
+			xfer_block->processed = USB_XFER_BLK_HANDLED;
 			break;
 
 		case XHCI_TRB_TYPE_NORMAL:
@@ -2480,7 +2472,7 @@ retry:
 				err = XHCI_TRB_ERROR_STALL;
 				goto errout;
 			}
-			xfer_block->processed = 1;
+			xfer_block->processed = USB_XFER_BLK_HANDLED;
 			break;
 
 		case XHCI_TRB_TYPE_EVENT_DATA:
@@ -2491,7 +2483,7 @@ retry:
 				goto errout;
 			}
 			if ((epid > 1) && (trbflags & XHCI_TRB_3_IOC_BIT))
-				xfer_block->processed = 1;
+				xfer_block->processed = USB_XFER_BLK_HANDLED;
 			break;
 
 		default:
@@ -2509,18 +2501,20 @@ retry:
 		if (xfer_block) {
 			xfer_block->trbnext = addr;
 			xfer_block->streamid = streamid;
-		}
-
-		if (!setup_trb && !(trbflags & XHCI_TRB_3_CHAIN_BIT) &&
-		    XHCI_TRB_3_TYPE_GET(trbflags) != XHCI_TRB_TYPE_LINK) {
-			break;
+			/* FIXME:
+			 * should add some code to process the scenario in
+			 * which endpoint stop command is comming in the
+			 * middle of many data transfers.
+			 */
+			pci_xhci_update_ep_ring(xdev, dev, devep, ep_ctx,
+					xfer_block->streamid,
+					xfer_block->trbnext, xfer_block->ccs);
 		}
 
 		/* handle current batch that requires interrupt on complete */
 		if (trbflags & XHCI_TRB_3_IOC_BIT) {
 			UPRINTF(LDBG, "trb IOC bit set\r\n");
-			if (epid == 1)
-				do_retry = 1;
+			do_retry = 1;
 			break;
 		}
 	}
diff --git a/devicemodel/hw/platform/usb_mouse.c b/devicemodel/hw/platform/usb_mouse.c
index 8de488f6e..4a52a695e 100644
--- a/devicemodel/hw/platform/usb_mouse.c
+++ b/devicemodel/hw/platform/usb_mouse.c
@@ -337,7 +337,7 @@ umouse_request(void *scarg, struct usb_data_xfer *xfer)
 			udata = data->buf;
 		}
 
-		xfer->data[idx].processed = 1;
+		xfer->data[idx].processed = USB_XFER_BLK_HANDLED;
 		idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
 	}
 
@@ -718,7 +718,7 @@ umouse_data_handler(void *scarg, struct usb_data_xfer *xfer, int dir,
 		if (data->buf != NULL && data->blen != 0)
 			break;
 
-		data->processed = 1;
+		data->processed = USB_XFER_BLK_HANDLED;
 		data = NULL;
 		idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
 	}
@@ -758,7 +758,7 @@ umouse_data_handler(void *scarg, struct usb_data_xfer *xfer, int dir,
 		if (len > 0) {
 			dev->newdata = 0;
 
-			data->processed = 1;
+			data->processed = USB_XFER_BLK_HANDLED;
 			data->bdone += 6;
 			memcpy(udata, &dev->um_report, 6);
 			data->blen = len - 6;
diff --git a/devicemodel/hw/platform/usb_pmapper.c b/devicemodel/hw/platform/usb_pmapper.c
index 153903448..d5d6e8d23 100644
--- a/devicemodel/hw/platform/usb_pmapper.c
+++ b/devicemodel/hw/platform/usb_pmapper.c
@@ -125,7 +125,7 @@ usb_dev_comp_req(struct libusb_transfer *libusb_xfer)
 		}
 	}
 
-	/* post process the usb transfer data */
+	/* handle the blocks belong to this request */
 	buf_idx = 0;
 	idx = req->blk_start;
 	for (i = 0; i < req->blk_count; i++) {
@@ -152,11 +152,13 @@ usb_dev_comp_req(struct libusb_transfer *libusb_xfer)
 		buf_idx += done;
 		block->bdone = done;
 		block->blen -= done;
+		block->processed = USB_XFER_BLK_HANDLED;
 		idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
 	}
 
 	if (short_data)
 		xfer->status = USB_ERR_SHORT_XFER;
+
 out:
 	/* notify the USB core this transfer is over */
 	if (g_ctx.notify_cb)
@@ -233,9 +235,9 @@ usb_dev_prepare_xfer(struct usb_data_xfer *xfer, int *count, int *size)
 	for (i = 0; i < xfer->ndata; i++) {
 		block = &xfer->data[idx];
 
-		if (block->processed) {
+		if (block->processed == USB_XFER_BLK_HANDLED ||
+				block->processed == USB_XFER_BLK_HANDLING) {
 			idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
-			c++;
 			continue;
 		}
 		if (block->buf && block->blen > 0) {
@@ -245,12 +247,20 @@ usb_dev_prepare_xfer(struct usb_data_xfer *xfer, int *count, int *size)
 			}
 			c++;
 			s += block->blen;
-
+		} else if (!block->buf || !block->blen) {
+			/* there are two cases:
+			 * 1. LINK trb is in the middle of trbs.
+			 * 2. LINK trb is a single trb.
+			 */
+			c++;
+			block->processed = USB_XFER_BLK_HANDLED;
+			idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
+			continue;
 		} else if (found) {
 			UPRINTF(LWRN, "find a NULL data. %d total %d\n",
 				i, xfer->ndata);
 		}
-		block->processed = 1;
+		block->processed = USB_XFER_BLK_HANDLING;
 		idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
 	}
 
@@ -558,7 +568,7 @@ usb_dev_prepare_ctrl_xfer(struct usb_data_xfer *xfer)
 		if (blk->blen > 0 && !ret)
 			ret = blk;
 
-		blk->processed = 1;
+		blk->processed = USB_XFER_BLK_HANDLED;
 		idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
 	}
 	return ret;
diff --git a/devicemodel/hw/usb_core.c b/devicemodel/hw/usb_core.c
index 53396f7e4..4c3ea3f56 100644
--- a/devicemodel/hw/usb_core.c
+++ b/devicemodel/hw/usb_core.c
@@ -114,7 +114,7 @@ usb_data_xfer_append(struct usb_data_xfer *xfer, void *buf, int blen,
 	xb->blen = blen;
 	xb->hci_data = hci_data;
 	xb->ccs = ccs;
-	xb->processed = 0;
+	xb->processed = USB_XFER_BLK_FREE;
 	xb->bdone = 0;
 	xfer->ndata++;
 	xfer->tail = (xfer->tail + 1) % USB_MAX_XFER_BLOCKS;
diff --git a/devicemodel/include/usb_core.h b/devicemodel/include/usb_core.h
index 64ca72458..3a9648a4f 100644
--- a/devicemodel/include/usb_core.h
+++ b/devicemodel/include/usb_core.h
@@ -78,6 +78,12 @@ enum usb_dev_type {
 	USB_DEV_PORT_MAPPER
 };
 
+enum usb_xfer_blk_stat {
+	USB_XFER_BLK_FREE = 0,
+	USB_XFER_BLK_HANDLING,
+	USB_XFER_BLK_HANDLED
+};
+
 struct usb_hci;
 struct usb_device_request;
 struct usb_data_xfer;
@@ -133,14 +139,14 @@ struct usb_hci {
  * of the buffer, i.e. len(buf) - len(consumed).
  */
 struct usb_data_xfer_block {
-	void	*buf;			/* IN or OUT pointer */
-	int	blen;			/* in:len(buf), out:len(remaining) */
-	int	bdone;			/* bytes transferred */
-	uint32_t processed;		/* device processed this + errcode */
-	void	*hci_data;		/* HCI private reference */
-	int	ccs;
-	uint32_t streamid;
-	uint64_t trbnext;		/* next TRB guest address */
+	void			*buf;	   /* IN or OUT pointer */
+	int			blen;	   /* in:len(buf), out:len(remaining) */
+	int			bdone;	   /* bytes transferred */
+	enum usb_xfer_blk_stat	processed; /* processed status */
+	void			*hci_data; /* HCI private reference */
+	int			ccs;
+	uint32_t		streamid;
+	uint64_t		trbnext;   /* next TRB guest address */
 };
 
 struct usb_data_xfer {