a basic timer in VHDL

Use a template from Quartus

Create a new vhdl file.

Select edit menu->insert template->

Select VHDL->Full Designs->Counters->Binary Count

Then modify then MAX_COUNT value depending on your input clock speed. i.e. how many input clock periods in 6.4us

Templates are agood way of finding out how to code various constructs

Hope this helps