Hardware interview practice
Rotate a tile in place with one memory port
Rotate a loaded square pixel tile 90 degrees clockwise in place when the local row-major memory permits only one synchronous read or one write per cycle.
Reviewed example
Work through one case
Input
N=2; row-major tile = [1, 2, 3, 4]Expected output
row-major tile after rotation = [3, 1, 4, 2]Saving the complete four-pixel cycle before any write prevents the single-port in-place update from destroying a later source pixel.
What to cover
Requirements
- Support N from 1 to 8 and exactly N times N pixels loaded in row-major order.
- Use the mapping (row, col) -> (col, N - 1 - row) without allocating a second tile.
- Save all four pixels in a cycle before writing any of them back.
- Use only a constant number of pixel registers and block external reads during rotation.
- After done, provide one-cycle external reads of the rotated row-major tile.