What the chip computes: the ASIC puzzle's Star Battle checker
The figures from the writeup, one per screen, in order.
Click or tap a cell to place a star. Check prints what the chip prints for the grid as drawn. The counts in the margins and the red cells are helpers; the chip itself only prints the message. Near miss loads a grid that breaks only the touching rule. Solution loads the key.
The 121-bit key as an 11 by 11 grid
The whole state of the chip is the 92 squares on the right. The grouping is what the rest of this section works out.
The key going in one bit per frame. Every number beside the grid is read from the flip-flops after that clock edge, nothing is computed by the animation.
Where a star’s earlier neighbours sit in the stream. Moving up one row is eleven cells back, so the three cells above are 10, 11 and 12 back, and the cell to the left is 1 back.
One star per cell, 121 runs. After each run the tally that moved names the cell’s region.
Left, the real map. Right, one of the alternatives: cell (0, 4) moved from region A to region B. Both have the key as their only solution.
The near miss with the fewest touching pairs, found with Z3 and run through the simulator. The pair is in red.