Routine that updates the mode 7 matrix parameters mirrors at $2E-$34 using the rotation and scale parameters at $36-$38. SMW calls it every frame in mode 7 bosses (when $0D9B is >= #$80), and the "Easy Mode 7 patch" calls it every frame in mode 7 levels, but you may need to call it manually if you're using mode 7 in special situations (for example, on the Overworld).
On SA-1 roms, this must be called when running on the SNES CPU.