grass growing is a block update, but so is breaking it. and placing a new dirt block, so I only need to respond to every third BUD, but a counter only outputs a short pulse, so I figured I'd use an latch and a timer to lengthen the pulse, which works...
but placing the new dirt block causes a block update, which the BUD-detector transmits through the newly placed block to the block placer, causing it to place another block
