Counter with period 1000

This is the first component of a larger timer circuit. The timer measures durations in blocks of 1000 clock cycles, so it needs a modulo-1000 pacer.

Build a counter that counts 0, 1, 2, … 999 and then wraps back to 0, so one full period takes exactly 1000 cycles. reset is synchronous, active-high, and forces the count to 0 at the next clock edge (it has priority over counting).