Master synchronization for multiple displays

In an embodiment, a display apparatus includes multiple physical interface circuits (PHYs) couple to respective displays. In a mirror mode, the PHYs may operate as masters. A primary master PHY may control a synchronization interface to one or more secondary master PHYs. The synchronization interface may include a start of frame signal that the primary master PHY may generate to indicate the beginning of a new frame. The secondary master PHYs may be configured to generate internal start of frame signals while independently processing the same display data as the primary master. If the internally-generated start of frame and the received start of frame occur within a window of tolerance of each other, then the secondary masters may continue to process the display data stream independently. A secondary master that detects the start of frames occur outside of the window of tolerance may resynchronize.