We used to run a fast counter while in every input loop. Whenever we were waiting for input, it would count until the input arrived. Since that was random, i.e. a counter that counted in microseconds, vs. an input from a human-operated keypad or keyboard, for example, the lsb was pretty reliably a random number. No matter how fast one types, or whatever, the keystrokes will vary enough in their timing as to be random. It's random enough, but not secure, as one who knows what's being done can then use a precisely controlled mechanism, e.g. another computer, to produce precisely timed inputs, which will aid in compromising the key generation algorithm, if that's how it's used.

RE