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If you are looking for freqeuncy generator for modelling then there are lots of possibilites and examples available on opencores. If you are looking for frequency derivatives for Physical implementations then I think you can generate frequency in odd and even fractions of the base frequency.
frequency can be easily divided in a multiple of 2T timing by using counter in behaviour structure. for any other frequency value, other frequency value, you need to use PLL method which shall be an analog method which are normally support by the chip company through their own build-in macro. as for multiplying frequency, it would be impractical, and i will recommend you to just use a higher freq crystal.