Hi Jack,
The problem is quite simple.
You are doing everything combinatorical.
Instead your Strobe signal has also to be generated inside a synchronous process.
You already created a synchronous delayed signal "a" from the Input "diffout".
For a first try:
Move your assignments for xorout, strobe_signal and diffstrobe into your process and see what happens.
I'm quite sure that this isn't the final solution, but at least your diffstrobe signal will not be shorter than a clock period anymore.
Of course, now you have to deal with pipelining problems. Just look at the RTL-Schematic to get an idea of your synthesis result.
Now rethink your approach and improve your coding.
Have a nice simulation
Eilert
