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18 1. INTRODUCTION
The main difference between the cellular routing architecture and the symmetrical
architecture is that the densest interconnections are taking place local
between the logical clusters and only a few (if there is any) longer connections
exists (e.g.: Xilinx XC6200, see Figure 1.9).
Figure 1.9: Cellular wiring
In most cases this architecture is used in fined grained FPGAs, where the clusters
are relatively simple and usually are containing only one logical element. In
order to make the routing process more effective, these logical cells are designed
in such way, that they may take part of the routing network between other logical
elements. The main drawbacks of the cellular routing architecture are the
followings:
• The combination pathways, which connects not only the neighborhood, may
have a huge delay.
• In case of CAD (Computer Aided Design) tools, there occurs significant
problem during the efficient placement of the circuit elements and the wiring
of the circuit of the architecture (place & routing).
• The area and delay requirements of the fine grained architecture are significant
compared to the number of logical element and routing resource