The Start-Of-Frame ( SOF ) signal, physically transmitted over the AXI4-Stream TUSER0 signal, marks the first pixel of a video frame. The SOF pulse is 1 valid transaction wide, and must coincide with the first pixel of the frame, as seen in This Figure . The SOF signal serves as a frame synchronization signal, which allows downstream cores to re-initialize, and detect the first pixel of a frame. The SOF signal may be asserted an arbitrary number of AP_CLK cycles before the first pixel value is presented on DATA , as long as a VALID is not asserted.