+
+ /*
+ * SCBs that want to send messages must always be
+ * at the head of their per-target queue so that
+ * ATN can be asserted even if the current
+ * negotiation agreement is packetized. If the
+ * target queue is empty, the SCB can be queued
+ * immediately. If the queue is not empty, we must
+ * wait for it to empty before entering this SCB
+ * into the waiting for selection queue. Otherwise
+ * our batching and round-robin selection scheme
+ * could allow commands to be queued out of order.
+ * To simplify the implementation, we stop pulling
+ * new commands from the host until the MK_MESSAGE
+ * SCB can be queued to the waiting for selection
+ * list.
+ */
+ test A, MK_MESSAGE jz batch_scb;
+
+ /*
+ * If the last SCB is also a MK_MESSAGE SCB, then
+ * order is preserved even if we batch.
+ */
+ test SCB_CONTROL, MK_MESSAGE jz batch_scb;
+
+ /*
+ * Defer this SCB and stop fetching new SCBs until
+ * it can be queued. Since the SCB_SCSIID of the
+ * tail SCB must be the same as that of the newly
+ * queued SCB, there is no need to restore the SCBID
+ * here.
+ */
+ or SEQ_FLAGS2, PENDING_MK_MESSAGE;
+ bmov MK_MESSAGE_SCB, REG0, 2;
+ mov MK_MESSAGE_SCSIID, SCB_SCSIID ret;
+
+batch_scb:
+ /*
+ * Otherwise just update the previous tail SCB to
+ * point to the new tail.
+ */