In the US, FAA Part 60 is your overall regulation. There are specifics in the Appendices. Appendix A is applicable to a FFS and the tables show which requirements apply to which of the device categories (A through D, with essentially everything applying to D, as you might expect).
This is a definition of the required standard of performance of the device though - it doesn't tell you how to achieve such standards (which the sim OEMs would in many cases consider to be IP I suspect)