[victor82]

Well, that code is module without any context (ie: connected to nothig), it just have 2 inputs (clk and rst), and an "output" with the current sum, after it reach the desired value it keep stuck there (until reset).

So as the simulation code shows, it just tick the clock (with the "yield" statement) and read the "output" register and print it.

Of course you could connect this "Project Euler 1 accelerator" to a CPU, a SoC or whatever, or just connect LEDs directly to "output"