Does the ext clk refer to an external clock in or the clock out of the crystal. I wish to feed an external clock in to the board.
Usually, yes, it is meant for external clock source. It is a good idea to mention which board exactly you have in mind, though.
Ah yes. It is the ice40HX1K-EVB however the other boards have the same or similar clock cct.
Can't insert/attach cct, sorry.
In iCE40HX1K-EVB we have already provided external clock. EXTCLK is generated by the 100Mhz oscillator CR1. Refer to this excerpt of the schematic: https://i.imgur.com/XKJaFmO.jpg