The routing process results in an output file specifying the used blocks and routing paths. It contains the resources that needs to be instantiated on the FPGA chip, however, the output format is not understood by the FPGA chip itself.
In the last step, the description of the chip is translated into the appropriate format, suitable for the chosen FPGA. That final file contains instructions readable by the configuration block of the desired chip.
Documenting the bitstream format for different FPGA chips is one of the most important tasks in the F4PGA Project!