Index: uspace/drv/bus/usb/xhci/transfers.c
===================================================================
--- uspace/drv/bus/usb/xhci/transfers.c	(revision eaf5e867c62f55c6dc6731c2cddfcdb4ba097009)
+++ uspace/drv/bus/usb/xhci/transfers.c	(revision 63adb1838e9362cf42099cd6f36d98e96f8cc005)
@@ -292,2 +292,66 @@
 	return EOK;
 }
+
+xhci_transfer_block_t* xhci_transfer_block_alloc(size_t buffer_size)
+{
+	assert(buffer_size);
+
+	xhci_transfer_block_t *block = malloc(sizeof(xhci_transfer_block_t));
+	block->buffer = (uintptr_t) malloc32(buffer_size);
+	block->total_size = buffer_size;
+	block->filled_size = 0;
+
+	return block;
+}
+
+void xhci_transfer_block_fini(xhci_transfer_block_t* block)
+{
+	assert(block);
+
+	free32((void*) block->buffer);
+	free(block);
+}
+
+int xhci_dequeue_transfer_block(xhci_hc_t* hc, size_t size, xhci_transfer_block_t** block)
+{
+	// TODO: obtain block from some global structure at HC
+
+	*block = xhci_transfer_block_alloc(size);
+	return EOK;
+}
+
+int xhci_free_transfer_block(xhci_hc_t* hc, xhci_transfer_block_t* block)
+{
+	assert(block);
+
+	// TODO: check if the block is not used?
+	// TODO: recycle block in some global structure at HC
+	xhci_transfer_block_fini(block);
+
+	return EOK;
+}
+
+int xhci_schedule_transfer_block(xhci_hc_t* hc, xhci_transfer_block_t* block)
+{
+	usb_transfer_batch_t* batch = block->transfer->batch;
+	uint8_t slot_id = batch->ep->hc_data.slot_id;
+	xhci_trb_ring_t* ring = hc->dcbaa_virt[slot_id].trs[batch->ep->endpoint];
+
+	xhci_trb_t trb;
+	memset(&trb, 0, sizeof(xhci_trb_t));
+	trb.parameter = block->buffer;
+
+	TRB_CTRL_SET_XFER_LEN(trb, block->filled_size);
+	// FIXME: TD size 4.11.2.4
+	TRB_CTRL_SET_TD_SIZE(trb, 1);
+
+	// we want an interrupt after this td is done
+	TRB_CTRL_SET_IOC(trb, 1);
+	TRB_CTRL_SET_TRB_TYPE(trb, XHCI_TRB_TYPE_NORMAL);
+	xhci_trb_ring_enqueue(ring, &trb, &block->transfer->interrupt_trb_phys);
+
+	// FIXME: Check return from xhci_trb_ring_enqueue.
+
+	hc_ring_doorbell(hc, slot_id, 1);
+	return EOK;
+}
Index: uspace/drv/bus/usb/xhci/transfers.h
===================================================================
--- uspace/drv/bus/usb/xhci/transfers.h	(revision eaf5e867c62f55c6dc6731c2cddfcdb4ba097009)
+++ uspace/drv/bus/usb/xhci/transfers.h	(revision 63adb1838e9362cf42099cd6f36d98e96f8cc005)
@@ -44,5 +44,19 @@
 
 	usb_transfer_batch_t* batch;
+
+	size_t completed_size;       /* Number of successfully transferred bytes. */
+	size_t scheduled_size;       /* Number of bytes scheduled for transfer. */
+	list_t active_blocks;        /* List of data blocks transferred right now. */
 } xhci_transfer_t;
+
+typedef struct {
+	link_t link;
+
+	uintptr_t buffer;            /* Physical address of the buffer start. */
+	size_t total_size;           /* Total size available in the block. */
+	size_t filled_size;          /* Size of the data in the block. */
+
+	xhci_transfer_t* transfer;   /* Current transfer or NULL. */
+} xhci_transfer_block_t;
 
 int xhci_init_transfers(xhci_hc_t*);
@@ -53,2 +67,8 @@
 int xhci_schedule_bulk_transfer(xhci_hc_t*, usb_transfer_batch_t*);
 int xhci_handle_transfer_event(xhci_hc_t*, xhci_trb_t*);
+
+xhci_transfer_block_t* xhci_transfer_block_alloc(size_t);
+void xhci_transfer_block_fini(xhci_transfer_block_t*);
+int xhci_dequeue_transfer_block(xhci_hc_t*, size_t, xhci_transfer_block_t**);
+int xhci_free_transfer_block(xhci_hc_t*, xhci_transfer_block_t*);
+int xhci_schedule_transfer_block(xhci_hc_t*, xhci_transfer_block_t*);