To designate registers for placement in the BLI area, set the BLI property on the register instance to TRUE and make sure there is a direct connection to/from the XPHY without any combinatorial logic.
Tip: If you set the BLI property on the
register instance to TRUE and the registers are not placed in a BLI location during
placement, check for other constraints that might be conflicting with the BLI
constraint, such as a Pblock or location constraint.