diff --git a/devicemodel/hw/pci/xhci.c b/devicemodel/hw/pci/xhci.c
index 4e1820111..a4823a32a 100644
--- a/devicemodel/hw/pci/xhci.c
+++ b/devicemodel/hw/pci/xhci.c
@@ -2650,12 +2650,11 @@ pci_xhci_xfer_complete(struct pci_xhci_vdev *xdev, struct usb_xfer *xfer,
 		trbflags = trb->dwTrb3;
 
 		UPRINTF(LDBG, "xfer[%d] done?%u:%d trb %x %016lx %x "
-			 "(err %d) IOC?%d, chained %d\r\n",
+			 "(err %d) IOC?%d, type %d\r\n",
 			 i, xfer->data[i].stat, xfer->data[i].blen,
-			 XHCI_TRB_3_TYPE_GET(trbflags), evtrb.qwTrb0,
-			 trbflags, err,
-			 trb->dwTrb3 & XHCI_TRB_3_IOC_BIT ? 1 : 0,
-			 xfer->data[i].chained);
+			 XHCI_TRB_3_TYPE_GET(trbflags), evtrb.qwTrb0, trbflags,
+			 err, trb->dwTrb3 & XHCI_TRB_3_IOC_BIT ? 1 : 0,
+			 xfer->data[i].type);
 
 		if (xfer->data[i].stat < USB_BLOCK_HANDLED) {
 			xfer->head = (int)i;
@@ -2668,14 +2667,14 @@ pci_xhci_xfer_complete(struct pci_xhci_vdev *xdev, struct usb_xfer *xfer,
 		edtla += xfer->data[i].bdone;
 
 		trb->dwTrb3 = (trb->dwTrb3 & ~0x1) | (xfer->data[i].ccs);
-		if (xfer->data[i].chained == 1) {
+		if (xfer->data[i].type == USB_DATA_PART) {
 			rem_len += xfer->data[i].blen;
 			i = (i + 1) % USB_MAX_XFER_BLOCKS;
 
-			/* When the chained == 1, this 'continue' will delay
-			 * the IOC behavior which could decrease the number
-			 * of virtual interrupts. This could GREATLY improve
-			 * the performance especially under ISOCH scenario.
+			/* This 'continue' will delay the IOC behavior which
+			 * could decrease the number of virtual interrupts.
+			 * This could GREATLY improve the performance especially
+			 * under ISOCH scenario.
 			 */
 			continue;
 		} else
@@ -2818,6 +2817,7 @@ pci_xhci_handle_transfer(struct pci_xhci_vdev *xdev,
 	struct		xhci_trb *setup_trb;
 	struct		usb_xfer *xfer;
 	struct		usb_block *xfer_block;
+	struct		usb_block *prev_block;
 	uint64_t	val;
 	uint32_t	trbflags;
 	int		do_intr, err;
@@ -2837,6 +2837,7 @@ retry:
 	do_retry = 0;
 	do_intr = 0;
 	setup_trb = NULL;
+	prev_block = NULL;
 
 	while (1) {
 		pci_xhci_dump_trb(trb);
@@ -2920,8 +2921,17 @@ retry:
 					trb->dwTrb2 & 0x1FFFF, (void *)addr,
 					ccs);
 
-			if (xfer_block && (trb->dwTrb3 & XHCI_TRB_3_CHAIN_BIT))
-				xfer_block->chained = 1;
+			if (!xfer_block) {
+				err = XHCI_TRB_ERROR_STALL;
+				goto errout;
+			}
+
+			if (trb->dwTrb3 & XHCI_TRB_3_CHAIN_BIT)
+				xfer_block->type = USB_DATA_PART;
+			else
+				xfer_block->type = USB_DATA_FULL;
+
+			prev_block = xfer_block;
 			break;
 
 		case XHCI_TRB_TYPE_STATUS_STAGE:
@@ -2948,6 +2958,10 @@ retry:
 			}
 			if ((epid > 1) && (trbflags & XHCI_TRB_3_IOC_BIT))
 				xfer_block->stat = USB_BLOCK_HANDLED;
+
+			if (prev_block && prev_block->type == USB_DATA_PART)
+				prev_block->type = USB_DATA_FULL;
+
 			break;
 
 		default:
diff --git a/devicemodel/hw/platform/usb_pmapper.c b/devicemodel/hw/platform/usb_pmapper.c
index 160d93c26..40e378c53 100644
--- a/devicemodel/hw/platform/usb_pmapper.c
+++ b/devicemodel/hw/platform/usb_pmapper.c
@@ -274,7 +274,8 @@ usb_dev_comp_cb(struct libusb_transfer *trn)
 			if (d > block->blen)
 				d = block->blen;
 
-			if (block->buf) {
+			if (block->type == USB_DATA_PART ||
+					block->type == USB_DATA_FULL) {
 				if (r->in == TOKEN_IN) {
 					memcpy(block->buf, buf + buf_idx, d);
 					buf_idx += d;
@@ -292,7 +293,7 @@ usb_dev_comp_cb(struct libusb_transfer *trn)
 			idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
 			i++;
 
-		} while (block->chained == 1);
+		} while (block->type == USB_DATA_PART);
 	}
 
 stall_out:
@@ -386,14 +387,15 @@ usb_dev_prepare_xfer(struct usb_xfer *xfer, int *count, int *size)
 			idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
 			continue;
 		}
-		if (block->buf && block->blen > 0) {
+		if (block->type == USB_DATA_PART ||
+				block->type == USB_DATA_FULL) {
 			if (!found) {
 				found = 1;
 				first = idx;
 			}
 			c++;
 			s += block->blen;
-		} else if (!block->buf || !block->blen) {
+		} else if (block->type == USB_DATA_NONE) {
 			/* there are two cases:
 			 * 1. LINK trb is in the middle of trbs.
 			 * 2. LINK trb is a single trb.
@@ -801,7 +803,7 @@ usb_dev_data(void *pdata, struct usb_xfer *xfer, int dir, int epctx)
 				continue;
 			}
 
-			if (xfer->data[idx].chained == 1) {
+			if (xfer->data[idx].type == USB_DATA_PART) {
 				idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
 				continue;
 			}
@@ -838,7 +840,8 @@ usb_dev_data(void *pdata, struct usb_xfer *xfer, int dir, int epctx)
 	if (!dir) {
 		for (i = 0, j = 0, buf_idx = 0; j < blk_count; ++i) {
 			b = &xfer->data[(blk_start + i) % USB_MAX_XFER_BLOCKS];
-			if (b->buf) {
+			if (b->type == USB_DATA_FULL ||
+					b->type == USB_DATA_PART) {
 				memcpy(&r->buffer[buf_idx], b->buf, b->blen);
 				buf_idx += b->blen;
 				j++;
@@ -850,13 +853,13 @@ usb_dev_data(void *pdata, struct usb_xfer *xfer, int dir, int epctx)
 		for (i = 0, j = 0, idx = blk_start; i < blk_count; ++i) {
 			int len = xfer->data[idx].blen;
 
-			if (len <= 0) {
+			if (xfer->data[idx].type == USB_DATA_NONE) {
 				idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
 				i--;
 				continue;
 			}
 
-			if (xfer->data[idx].chained == 1) {
+			if (xfer->data[idx].type == USB_DATA_PART) {
 				r->trn->iso_packet_desc[j].length += len;
 				idx = (idx + 1) % USB_MAX_XFER_BLOCKS;
 				continue;
diff --git a/devicemodel/hw/usb_core.c b/devicemodel/hw/usb_core.c
index e1d1b9ccd..ce1f61c2d 100644
--- a/devicemodel/hw/usb_core.c
+++ b/devicemodel/hw/usb_core.c
@@ -116,7 +116,7 @@ usb_block_append(struct usb_xfer *xfer, void *buf, int blen,
 	xb->ccs = ccs;
 	xb->stat = USB_BLOCK_FREE;
 	xb->bdone = 0;
-	xb->chained = 0;
+	xb->type = USB_DATA_NONE;
 	xfer->ndata++;
 	xfer->tail = (xfer->tail + 1) % USB_MAX_XFER_BLOCKS;
 	return xb;
diff --git a/devicemodel/include/usb_core.h b/devicemodel/include/usb_core.h
index 24cff1f2f..0c1dd6a56 100644
--- a/devicemodel/include/usb_core.h
+++ b/devicemodel/include/usb_core.h
@@ -142,6 +142,12 @@ struct usb_hci {
 	int	hci_port;
 };
 
+enum usb_block_type {
+	USB_DATA_NONE,
+	USB_DATA_PART,
+	USB_DATA_FULL
+};
+
 /*
  * Each xfer block is mapped to the hci transfer block.
  * On input into the device handler, blen is set to the lenght of buf.
@@ -155,9 +161,9 @@ struct usb_block {
 	enum usb_block_stat	stat;      /* processed status */
 	void			*hci_data; /* HCI private reference */
 	int			ccs;
-	int			chained;
 	uint32_t		streamid;
 	uint64_t		trbnext;   /* next TRB guest address */
+	enum usb_block_type	type;
 };
 
 struct usb_xfer {