@devyte - [review integer ranges for overflow, minor constness ]

edit: divide by zero if they feed it 0Hz, uint32_t overflow below 233Hz
edit2: there's no overflow, my test program above was mixing ints and unsigned ints (corrected). The real code was correct. I knew I'd checked my math twice to insure I stayed within an unsigned int!

Might want to limit the lower end even further, as a single byte read or write is ~78ms at 250Hz.
(start, 7 bits address, read/write, ack, 8 bits data, ack, stop). Maybe somewhere around 500Hz to 1KHz would be a better lower limit. I don't expect any more than a few people trying to run it lower than 10KHz, normally. There were some radio PLLs that needed ~ 10KHz bus clock back in the '80s, but that's ancient history.