VHDL Question

Check your warnings. You have "count" (a 32-bit integer) going to ten billion. This is not a sensible way to make sawtooth wave in any event.

You seem to want to do this without even a basic understanding of VHDL. Find a good tutorial on VHDL and learn it. Then making a square wave will be trivial. I'm afraid my favorite VHDL books are all out of print, but there are good ones out there.