SNLA474A October   2024  – October 2024 DS90UB971-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 Typical Test Standards Overview
    1. 2.1 ISO 10605 Standard
    2. 2.2 Performance Status Categorization
  6. 3 FPD-Link Hardware Optimizations
    1. 3.1 Connector Grounding
    2. 3.2 PCB to Enclosure Grounding
    3. 3.3 MODE Selection
  7. 4 FPD-Link Software Optimizations
    1. 4.1 LOCK Detection Tuning
    2. 4.2 Parity Error Handling
    3. 4.3 Forward Error Correction
      1. 4.3.1 FEC Test Capabilities
  8. 5 Optimization Test Data
    1. 5.1 Baseline Hardware - No Software Optimization
    2. 5.2 Optimized Hardware - No Software Optimization
    3. 5.3 Optimized Hardware and Software
  9. 6 Example Scripts for Software Optimization
  10. 7 Additional System Level Software Options
  11. 8 Summary
  12. 9 References
  13. 10Revision History

4.3 Forward Error Correction

Select FPD-Link devices within the FPD-Link III and FPD-Link IV product families include forward error correction (FEC) functionality within the FPD-Link forward channel path. Forward error correction utilizes unoccupied channel bandwidth to send error correcting code words along with the forward channel data payload which allows the downstream deserializer to correct transient errors. FEC functionality is available on the following devices:

  • DS90UB971-Q1
  • DS90UB953-Q1
  • DS90UB953A-Q1
  • DS90UB935-Q1
  • DS90UB635-Q1
  • DS90UB960-Q1
  • DS90UB962-Q1
  • DS90UB662-Q1
  • DS90UB9702-Q1
  • DS90UB9722-Q1
  • DS90UB9724-Q1
  • DS90UB9742-Q1

FEC functionality is not available on the following devices:

  • DS90UB933-Q1
  • DS90UB913A-Q1
  • DS90UB913Q-Q1
  • DS90UB934-Q1
  • DS90UB954-Q1
  • DS90UB936-Q1
  • DS90UB638-Q1
  • DS90UB964-Q1

To utilize FEC functionality, both the serializer and deserializer device within the link pair must support FEC.

There are three selectable FEC modes available with different code sizes for the inserted error correcting codes (ECC):

  • 6-bit FEC
  • 7-bit FEC
  • 8-bit FEC

When FEC is enabled, the serializer sends multiple (X) data frames, followed by multiple (Y) frames containing error correcting codes (ECC) in sequence. The error correcting code chunks (Y) protect CSI-2 data, GPIO data, and I2C data by allowing the deserializer to detect 2-bit errors, and correct 1-bit errors within the data chunk (X) much like the data protection within the packet header for CSI-2 data.

8-Bit FEC Sequence Example Figure 4-4 8-Bit FEC Sequence Example

Each FEC mode defines a ratio of (X) data frames and (Y) ECC frames sent within a 130 frame DCA sequence. The 6-bit mode protects smaller chunks of data, but correction codes are sent more frequently. The 8-bit mode protects larger chunks of data, with correction codes sent less frequently. The ratios are defined below:

Table 4-1 ECC Code Transmission
FEC Mode Number of Data Frames (X) Number of ECC Frames (Y) ECC Frames Per DCA Sequence Data Frames Per DCA Sequence FEC Overhead
6-bit 20 6 30 100 23%
7-bit Alternating 36, 37 7 21 109 16%
8-bit 57 8 16 114 12%

FEC overhead reduces the allowable payload capability for video in the FPD-Link forward channel pipeline. Care must be taken to verify that the link video bandwidth after FEC is enabled can meet the application's needs.

Table 4-2 FEC Overhead Impact Examples
Device FPD-Link Rate (Gbps) Max CSI-2 Bandwidth (Gbps) FEC Mode Max CSI-2 Bandwidth FEC Enabled (Gbps)
DS90UB971-Q1 7.55 6 6-bit 4.8
DS90UB971-Q1 7.55 6 7-bit 5.1
DS90UB971-Q1 7.55 6 8-bit 5.3
DS90UB953-Q1 4 3.2 6-bit 2.6
DS90UB953-Q1 4 3.2 7-bit 2.7
DS90UB953-Q1 4 3.2 8-bit 2.8
DS90UB935-Q1 4 2.528 6-bit 2.528

(Lesser of 2.528Gbps and 3.2Gbps/1.23)
DS90UB935-Q1 4 2.528 7-bit 2.528

(Lesser of 2.528Gbps and 3.2Gbps/1.16)
DS90UB935-Q1 4 2.528 8-bit 2.528

(Lesser of 2.528Gbps and 3.2Gbps/1.12)

To enable FEC functionality, configure deserializer register 0x4A (port specific):

  • 6-bit FEC: 0x4A = 0x01
  • 7-bit FEC: 0x4A = 0x02
  • 8-bit FEC: 0x4A = 0x03

The deserializer notifies the serializer to enter FEC mode via the back channel automatically.