Either in the VBIOS (I do custom work on VBIOS ROMs for coin to do this, as well as timings), or me personally, I use a set of tools I wrote.

You can see it here, in the left terminal window - this pic was to show my RX 580 8G successfully mining stable with 30.2MH/s @ 0.7875V: https://ottrbutt.com/tmp/580UV.jpg