PDP11, all VAX: better manage VH input FIFO empty transition status (…

…Ed Marr)
simh · Aug 16, 2018 · c833c93 · c833c93
1 parent 664a2d5
commit c833c93
Showing 1 changed file with 6 additions and 3 deletions.
diff --git a/PDP11/pdp11_vh.c b/PDP11/pdp11_vh.c
@@ -779,10 +779,9 @@ static int32 fifo_get ( int32   vh  )
 {
     int32   data, i;
 
-    if (rbuf_idx[vh] == 0) {
-        vh_csr[vh] &= ~CSR_RX_DATA_AVAIL;
+    if (rbuf_idx[vh] == 0)
         return (0);
-    }
+
     /* pick off the first character, mark valid */
     data = vh_rbuf[vh][0] | RBUF_DATA_VALID;
     /* move the remainder up */
@@ -815,6 +814,10 @@ static int32 fifo_get ( int32   vh  )
             }
         }
     }
+
+    if (rbuf_idx[vh] == 0)                  /* FIFO just became empty? */
+        vh_csr[vh] &= ~CSR_RX_DATA_AVAIL;   /* clear CSR bit ti indicate this */
+
     /* Reschedule the next poll preceisely so that the 
        programmed input speed is observed. */
     sim_clock_coschedule_abs (vh_poll_unit, tmxr_poll);