What is definition of placement blockage ?

Placement blockages are areas that leaf cells must avoid during placement and legalization, including overlapping any part of the placement blockage. Placement blockages can be hard or soft.

-- A hard blockage prevents cells from being placed in the blockage area.

-- A soft blockage restricts the course placer from putting cells in the blockage area, but optimization and legalization can place cells in a soft blockage area.

If you define both hard and soft placement blockages in your design, the hard placement blockages take priority over the soft placement blockages in places where they overlap.

You can define a placement blockage by either specifying a region around fixed macros ( keepout margins ) or by specifying a rectangular blockage area ( area-based placement blockages).

(placement keepout margin)

A keepout margin is a region around the boundary of fixed macros in your design in which no other cells are placed.