No BMODE              BMODE
                     +-----+------+      +-----+------+
      R0 ---> area:  | 26  |  0   |      | 26  |  0   |
                     +-----+------+      +-----+------+
                     |  reserved  |      |  reserved  |
                     +------------+      +------------+
                     |    buf     |      |    buf     |
                     +------------+      +------------+
                     |    wcnt    |      |    wcnt    |
                     +------------+      +------------+
                     |      0     |      |mapping bits|
                     +------------+      +------------+
                                         |     0      |
                                         +------------+