As a rule core processor selected during previous codesign stage is unable to provide suitable performance of the system (if so the objective is reached). The common way to solve this problem is to partition the system into common part and critical blocks. These blocks concentrate time-consuming computations so their acceleration whould generally improve performance of the system as whole.

There are several ways to extract critical blocks; profiling is commonly used for this purpose. Extracted blocks are subjects to implement as separate hardware extensions.