The datasheet states there is an API ROM Routine for setting the FPO frequency. It shows how it works (parameter, etc.), but it doesn't show how to use it. I don't see anywhere what the API command code is (I assume it's like the IAP commands, but don't know).
Is there any example code (preferably for IAR) that shows how to set the frequency of the FRO? Something that shows implementation of set_fro_frequency() referenced in the manual.
And let me just complain one more time about not updating LPC_Open for the LPC84X. I realize there would be some work involved, but since you're not doing it, I'm wasting good development time making it work so I can use it (port my existing LPC824 code over) instead of developing my application.