1.What is Frame-Sync
Image sensor works in frame-based behavior. By receiving SOF(Start-of-Frame) package via MIPI, ISP will generate Vsync signal to APMCU, CCU and related modules. Frame-length is defined as the time period between two consecutive Vsync signals. Frame-sync means make 2 sensor’s frame length and Vsync signal timing identical as possible under stereo scenario.
2.Purpose of Frame-Sync
Some of stereo camera feature needs the two image received from each side of sensors should be exposed in the very close timing to ensure the quality of feature effect, e.g. Refocus, Bokeh, AE-Sync. Which means that frame start/end timing of two sensors should be nearly the same. CCU will achieve this by calculating frame-length from shutter and fps of two sensors, and add compensation time onto frame-length of one of the two sensors if the two Vsync timing differs over required threshold.