The DS90UB954-Q1 implements logic to detect skew between video signaling from attached Sensors. For each input port, the DS90UB954-Q1 provides the ability to capture a timestamp for both a start-of-frame and start-of-line event. Comparison of timestamps can provide information on the relative skew between the ports. Start-of-frame timestamps are generated at the active edge of the Vertical Sync signal in Raw mode. Start-of-line timestamps are generated at the start of reception of the Nth line of video data after the start-of-frame for either mode of operation. The function does not use the Line Start (LS) packet or Horizontal Sync controls to determine the start of lines. Timestamp operation is not supported if multiple video streams (Virtual Channels) are present on a single Rx port.

The skew detection can run in either a FrameSync mode or free-run mode.

Skew detection can be individually enabled for each RX port.

For start-of-line timestamps, a line number must be programmed. The same line number is used for all channels. Prior to reading timestamps, the TS_FREEZE bit for each port that will be read should be set. This will prevent overwrite of the timestamps by the detection circuit until all timestamps have been read. The freeze condition will be released automatically once all frozen timestamps have been read. The freeze bits can also be cleared if it does not read all the timestamp values.

The TS_STATUS register includes the following:

• Flags to indicate multiple start-of-frame per FrameSync period
• Flag to indicate Timestamps Ready

• Flags to indicate Timestamps valid (per port) – if ports are not synchronized, all ports may not indicate valid timestamps

The Timestamp Ready flag will be cleared when the TS_FREEZE bit is cleared.