argh, found the blackbox problem: yosys is "doing the right thing" and

argh, found the blackbox problem: yosys is "doing the right thing" and
identifying spblock as a cell (there are 4 used, therefore it gets identified
as a cell).
also because the blackbox is empty, yosys is optimising it out.
therefore, solution: put something (q = d) into the blackbox, and make
4 each with different names.
yes, it is awful, but it works