code: function() {
  		if ((this.loopyV & 0x7000) != 0x7000) {
  			// fine Y < 7: increment
  			this.loopyV += 0x1000;
  		} else {
  			// fine Y at maximum: reset fine Y, increment coarse Y
  			this.loopyV &= ~0x7000; 
  
  			var coarseY = (this.loopyV & 0x03e0) >>> 5;
  			if (coarseY == 29) {
  				// switch vertical nametable
  				coarseY = 0;
  				this.loopyV ^= 0x0800;
  			} else if (coarseY == 31) {
  				// reset coarse Y without switching nametable
  				coarseY = 0;
  			} else {
  				// simply increment coarse Y
  				coarseY += 1;
  			}
  
  			// set coarse Y in loopy_v
  			this.loopyV = (this.loopyV & ~0x03e0) | (coarseY << 5);
  		}
  
  		this.y = ( this.loopyV & 0x7000 ) >> 12;
  	}
docs: Increment Y scroll in loopy_v.
  TODO optimizations