What is the lowest latency communication method between a computer and a microcontroller?

Question

I have a project in which I need to have the lowest latency possible (in the 1-100 microseconds range at best) for a communication between a computer (Windows + Linux + MacOSX)

Answer 1

To answer the question, there are two low latency methods:

1. Serial or parallel port. It is possible to get latency down to the millisecond scale, although your performance may vary depending on manufacturer. One good brand is Brainboxes, although their cards can cost over $100!

2. Write your own driver. It should be possible to achieve latencies on the order of a few hundred micro seconds, although obviously the kernel can interrupt your process mid-way if it needs to serve something with a higher priority. This how a lot of scientific equipment actually works. (and a lot of the people telling you that a PC can't be made to work on short deadlines are wrong).