Aspect ratio of Pblock

[Syed Ahmed]

Can somebody explain how the default value of ASPECT_RATIO in the PBlockGenerator.java was chosen? I am reading some literature on the effect of aspect ratio of a pblock on routing (https://arxiv.org/abs/1904.10646) and was wondering what are the best practices for choosing an aspect ratio. Thank you in advance! If there were some literature used to design the PBlockGenerator, would really appreciate if you could also give a pointer to those. 

[RapidWright]

The PBlockGenerator was written with the goal of finding pblocks that could easily allow a module to be placed and routed within the rectangle and maximize their relocatability (number of valid locations with the same footprint).  In order to maximize relocatability, you want an aspect ratio that is taller and narrow because of Xilinx's columnar-based architecture.  Resources are generally homogeneous in the vertical direction, yet not predictably regular in the horizontal direction.  Much of the values set in the PBlockGenerator were found after several experiments were performed.  

Unfortunately, there is no published work associated with building the PBlockGenerator, but if you are interested in collaborating on improvements, let us know!