GTS HDMI Intel® FPGA IP User Guide

ID 823533
Date 11/25/2024
Public
Document Table of Contents

7.1.1. Sink Word Alignment and Channel Deskew

The input stage of the sink is responsible for synchronizing the incoming parallel data channels correctly. The synchronization is split to two stages: word alignment and channel deskew.
Table 35.  Synchronization Stages
Stage Description
Word Alignment TMDS Mode
  • Correctly aligns the incoming parallel data to word boundaries using bit-slip and pattern-matching technique.
  • TMDS encoding does not guarantee unique control codes, but the core can still use the sequence of continuous symbols found in data and video preambles to align.
  • The alignment algorithm searches for 8 consecutive 0×54 or 0×ab corresponding to the data and video preambles.
    Note: The preambles are also present in Digital Video Interface (DVI) coding.
  • The alignment logic asserts a marker indicator when the 8 consecutive signals are detected. Similarly, the logic infers alignment loss when 8K symbol clocks elapse without a single marker assertion.
Channel Deskew
  • When the data channels are aligned, the core then attempts to deskew each channel.
  • The sink core deskews at the rising edge of the marker insertion.
  • For every correct deskewed lane, the marker insertion will appear in all three TMDS encoded streams.
  • The sink core deskews using three dual-clock FIFOs.
  • The dual-clock FIFOs also synchronize all three data streams to the blue channel clock to be used later throughout the decoder core.
Figure 32. Channel Deskew DCFIFO ArrangementThe figure below shows the signal flow diagram of the deskew logic.

The FIFO read signal of the channels is normally asserted. The sink core deasserts a particular FIFO read signal if a marker appears at its output and not in the other two FIFO outputs. By deasserting, the sink core stalls the data stream for sufficient cycles to remove the channel skew. If any of the FIFO channels overflow, the sink core asserts a reset signal which propagates backwards to the word alignment logic.