Design a Lattice FPGA HDMI Transmission Scheme

Here's a comprehensive Lattice FPGA HDMI Transmission Scheme design using low-power Lattice FPGAs (e.g., ECP5 or CrossLink-NX). This solution covers hardware, FPGA logic, and software components for robust HDMI signal transmission:

1. System Overview
Target Devices: Lattice ECP5 (for cost-sensitive designs) or CrossLink-NX (for embedded MIPI DSI/CSI-to-HDMI bridging)

HDMI Version: 1.4b (Supports 1080p60, with optional TMDS scrambling for EMI reduction)

Key Features:

• TMDS Signal Generation (FPGA-native or external PHY)
• EDID Management (Hot-Plug Detect, DDC I2C)
• Color Space Conversion (RGB ↔ YCbCr 4:4:4)
• Audio Embedding (I2S to HDMI Audio Packet)

2. Hardware Design
A. Block Diagram

[Video Source] → [Lattice FPGA] → [HDMI Transmitter] → [HDMI Connector]
                   (ECP5/CrossLink)   (e.g., IT66121 or native TMDS)

B. Critical Components

1. FPGA Selection:

• ECP5-85F (For 1080p60 with internal LVDS→TMDS conversion)
• CrossLink-NX-17 (For MIPI DSI/CSI to HDMI conversion)

1. HDMI PHY Options:

• Internal TMDS (ECP5 LVDS pins + SERDES)
• External PHY (e.g., IT66121 for simplified design)

1. Clock Architecture:

• 148.5 MHz for 1080p60 (Pixel Clock)
• 27 MHz for I2C/EDID management
• Optional PLL for audio clock (e.g., 12.288 MHz for 48kHz audio)

1. Connectors:

• HDMI Type A (Standard 19-pin)
• ESD Protection (TVS diodes on TMDS lines)

3. FPGA Logic Design (Verilog/VHDL)
A. TMDS Encoder Core

verilog

module tmds_encoder (
  input clk_pixel,
  input [7:0] data,
  input [1:0] control,
  output [9:0] tmds
);
  // Implement DVI 1.0 Spec TMDS encoding
  // Includes XOR/XNOR reduction and DC balancing
endmodule

B. Video Timing Controller

verilog

module video_timing (
  output [11:0] h_count,
  output [11:0] v_count,
  output h_sync, v_sync, data_enable
);
  // Generates 1080p60 timing:
  // Active: 1920x1080, Front Porch/Sync/Back Porch
endmodule

C. I2C EDID Handler

verilog

module edid_reader (
  inout  sda,
  output scl,
  input  hpd,
  output [7:0] edid_data
);
  // Responds to DDC requests and serves EDID
  // Implements I2C slave at address 0x50
endmodule

4. Software Components
A. Lattice Diamond/Primary Configuration

1. Pin Constraints (.lpf file for ECP5):

LOCATE COMP "tmds_clk_p" SITE "E4";
IO_TYPE "LVDS25";

1. PLL Configuration:

• Generate 148.5 MHz from 25 MHz oscillator
• Phase-align TMDS clock/data

B. Embedded RISC-V Core (For Smart HDMI)
Use Lattice Propel to add soft-core CPU for:

• EDID parsing
• Dynamic resolution switching
• Audio packet generation

5. Signal Integrity Considerations

1. PCB Layout Rules:

• TMDS Differential Pairs: 100Ω impedance, length-matched (±50mil)
• Layer Stackup: Route on adjacent layers with ground plane
• Termination: On-die termination (ODT) in ECP5

1. EMI Reduction:

• Enable TMDS scrambling (HDMI 1.3+)
• Spread-spectrum clocking (if supported by sink)

6. Testing & Validation

1. Test Pattern Generator:

Implement color bars/ramp in FPGA logic

verilog

case (h_count[3:0])
  0: {r,g,b} = 8'hFF; // White
  1: {r,g,b} = 8'h00; // Black
  // ... Color pattern
endcase

1. Compliance Testing:

Use HDMI analyzer (e.g., Quantum Data)

Verify:

• TMDS eye diagram
• EDID response time (<200ms)
• Hot-plug detection

7. Example Implementation (ECP5-85F)
Bill of Materials

Resource Utilization (Estimate)

• Logic Cells: ~5k LUTs (for 1080p60)
• Memory: 2x SPRAM (for line buffering)
• PLLs: 1 (for pixel clock generation)

8. Advanced Features (Optional)

1. HDCP Encryption:

• Requires licensed IP core
• CrossLink-NX supports hard-IP HDCP 1.4

1. 4K Support:

• Use ECP5-85F with external TMDS buffer
• Requires dual-link HDMI or switch to DisplayPort

1. Embedded Audio:

verilog

audio_packetizer u_audio (
  .i2s_data(audio_data),
  .hdmi_header(audio_header),
  .data_island(packet_data)
);

Debugging Tips

1. No Signal?:

• Check HPD (Hot Plug Detect) pull-up
• Verify DDC I2C communication with logic analyzer

1. Sparkles/Garbled Image:

• Recheck SERDES alignment
• Validate TMDS termination

1. Use Lattice Reveal:

tcl

reveal_insert -port h_sync -name h_sync_debug
reveal_trigger -condition {h_count == 0}

This design balances cost, performance, and flexibility. For production designs, consider Lattice's HDMI IP核 or Reference Designs (like the ECP5 Video Interface Kit).