E-Tile Hard IP User Guide: E-Tile Hard IP for Ethernet and E-Tile CPRI PHY Intel® FPGA IPs

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ID 683468
Date 7/23/2024
Public
Document Table of Contents
Document Table of Contents x
1. About E-Tile Hard IP User Guide 2. About the E-Tile Hard IP for Ethernet Intel® FPGA IP Core 3. About the E-Tile CPRI PHY Intel® FPGA IP 4. Supported Tools 5. E-Tile Hard IP User Guide Archives
2. About the E-Tile Hard IP for Ethernet Intel® FPGA IP Core x
2.1. E-Tile Hard IP for Ethernet Intel® FPGA IP Supported Features 2.2. E-Tile Hard IP for Ethernet Intel® FPGA IP Overview 2.3. IP Core Device Family and Speed Grade Support 2.4. IP Core Verification 2.5. Resource Utilization 2.6. Release Information 2.7. Getting Started 2.8. E-Tile Hard IP for Ethernet Intel FPGA IP Parameters 2.9. Functional Description 2.10. Reset 2.11. Interfaces and Signals 2.12. Register Descriptions 2.13. Document Revision History for the E-Tile Hard IP for Ethernet Intel FPGA IP Core
2.3. IP Core Device Family and Speed Grade Support x
2.3.1. E-Tile Hard IP for Ethernet Intel® FPGA IP Device Family Support 2.3.2. E-Tile Hard IP for Ethernet Intel® FPGA IP Device Speed Grade Support
2.4. IP Core Verification x
2.4.1. Simulation Environment 2.4.2. Compilation Checking 2.4.3. Hardware Testing
2.7. Getting Started x
2.7.1. Installing and Licensing Intel® FPGA IP Cores 2.7.2. Specifying the IP Core Parameters and Options 2.7.3. Generated File Structure 2.7.4. Integrating Your IP Core in Your Design 2.7.5. IP Core Testbenches 2.7.6. Compiling the Full Design
2.7.1. Installing and Licensing Intel® FPGA IP Cores x
2.7.1.1. Intel® FPGA IP Evaluation Mode
2.7.4. Integrating Your IP Core in Your Design x
2.7.4.1. Channel Placement 2.7.4.2. Pin Assignments 2.7.4.3. Clock Requirements 2.7.4.4. External Time-of-Day Module for Variations with 1588 PTP Feature 2.7.4.5. SDC for Multiple E-Tile Instances
2.7.4.1. Channel Placement x
2.7.4.1.1. Guidelines and Restrictions for 24-bonded Channels Variant 2.7.4.1.2. Guidelines and Restrictions for 16-bonded Channels Variant
2.8. E-Tile Hard IP for Ethernet Intel FPGA IP Parameters x
2.8.1. Parameter Editor Parameters 2.8.2. RTL Parameters
2.9. Functional Description x
2.9.1. E-Tile Hard IP for Ethernet Intel FPGA IP MAC 2.9.2. 1588 Precision Time Protocol Interfaces 2.9.3. PCS, OTN, FlexE, and Custom PCS Modes 2.9.4. Auto-Negotiation and Link Training 2.9.5. TX and RX RS-FEC 2.9.6. PMA Direct Mode 2.9.7. Dynamic Reconfiguration 2.9.8. Ethernet Adaptation Flow for 10G/25G and 100G/4x25G Dynamic Reconfiguration Design Example 2.9.9. Ethernet Adaptation Flow for 100G (CAUI-2) PAM4 <---> 100G (CAUI-4) NRZ Dynamic Reconfiguration Design Example 2.9.10. Ethernet Adaptation Flow with PTP or with External AIB Clocking 2.9.11. Ethernet Adaptation Flow with Non-external AIB Clocking
2.9.1. E-Tile Hard IP for Ethernet Intel FPGA IP MAC x
2.9.1.1. MAC TX Datapath 2.9.1.2. MAC RX Datapath 2.9.1.3. Congestion and Flow Control Using PAUSE or Priority Flow Control (PFC) 2.9.1.4. Pause Control and Generation Interface 2.9.1.5. Pause Control Frame Filtering 2.9.1.6. Link Fault Signaling 2.9.1.7. Order of Ethernet Transmission
2.9.1.1. MAC TX Datapath x
2.9.1.1.1. TX Preamble, Start, and SFD Insertion 2.9.1.1.2. Source Address Insertion 2.9.1.1.3. Length/Type Field Processing 2.9.1.1.4. Frame Padding 2.9.1.1.5. Frame Check Sequence (CRC-32) Insertion 2.9.1.1.6. Inter-Packet Gap Generation and Insertion
2.9.1.2. MAC RX Datapath x
2.9.1.2.1. RX Preamble Processing 2.9.1.2.2. RX Strict SFD Checking 2.9.1.2.3. RX FCS Checking 2.9.1.2.4. RX Malformed Packet Handling 2.9.1.2.5. Removing PAD Bytes and FCS Bytes from RX Frames 2.9.1.2.6. RX Undersized Frames, Oversized Frames, and Frames with Length Errors 2.9.1.2.7. Inter-Packet Gap
2.9.1.3. Congestion and Flow Control Using PAUSE or Priority Flow Control (PFC) x
2.9.1.3.1. Conditions Triggering XOFF Frame Transmission 2.9.1.3.2. Conditions Triggering XON Frame Transmission
2.9.1.6. Link Fault Signaling x
2.9.1.6.1. Determining Link Fault Condition
2.9.2. 1588 Precision Time Protocol Interfaces x
2.9.2.1. Implementing a 1588 System That Includes a E-Tile Hard IP for Ethernet Intel FPGA IP 2.9.2.2. PTP Timestamp Accuracy 2.9.2.3. PTP Transmit Functionality 2.9.2.4. PTP Receive Functionality 2.9.2.5. External Time-of-Day Module for 1588 PTP Variations 2.9.2.6. PTP Timestamp and TOD Formats 2.9.2.7. 10G/25G TX and RX Unit Interval Adjustment 10G/25G UI Adjustment Calculation 2.9.2.8. 10G/25G TX and RX PTP Extra Latency 2.9.2.9. 100G PTP TX User Flow 2.9.2.10. 100G PTP RX User Flow 2.9.2.11. 100G RX Virtual Lane Offset Calculation for No FEC Variants 2.9.2.12. 100G UI Adjustment 2.9.2.13. Minimum and Maximum Reference Time (TAM) Interval for UI Measurement (Hardware) 2.9.2.14. PTP System Considerations 2.9.2.15. Logic Lock Regions Requirements for PTP Accuracy Advanced Mode
2.9.3. PCS, OTN, FlexE, and Custom PCS Modes x
2.9.3.1. PCS Only Mode 2.9.3.2. OTN Mode 2.9.3.3. FlexE Mode 2.9.3.4. Custom PCS Mode
2.10. Reset x
2.10.1. Reset Sequence
2.10.1. Reset Sequence x
2.10.1.1. Reset Sequence with External AIB Clocking
2.11. Interfaces and Signals x
2.11.1. TX MAC Interface to User Logic 2.11.2. RX MAC Interface to User Logic 2.11.3. TX PCS Interface to User Logic 2.11.4. RX PCS Interface to User Logic 2.11.5. FlexE and OTN Mode TX Interface 2.11.6. FlexE and OTN Mode RX Interface 2.11.7. TX Custom PCS Interface to User Logic 2.11.8. RX Custom PCS Interface to User Logic 2.11.9. PMA Direct Interface 2.11.10. Custom Rate Interface 2.11.11. Deterministic Latency Interface 2.11.12. 1588 PTP Interface 2.11.13. Ethernet Link and Transceiver Signals 2.11.14. Reconfiguration Interfaces and Signals 2.11.15. Miscellaneous Status and Debug Signals 2.11.16. Reset Signals 2.11.17. Clocks
2.11.14. Reconfiguration Interfaces and Signals x
2.11.14.1. Ethernet Reconfiguration Interfaces 2.11.14.2. Transceiver Reconfiguration Interfaces 2.11.14.3. RS-FEC Reconfiguration Interfaces 2.11.14.4. PTP Reconfiguration Interfaces
2.11.17. Clocks x
2.11.17.1. Asynchronous Adapter Clock in 10G/25G Mode 2.11.17.2. Asynchronous Adapter Clock in 100G Mode 2.11.17.3. Clock Network Use Cases
2.11.17.3. Clock Network Use Cases x
2.11.17.3.1. Single 25G Ethernet Channel (with FEC) 2.11.17.3.2. Single 10G Ethernet Channel (without FEC) 2.11.17.3.3. Four 25G Ethernet Channels (with FEC) within a Single FEC Block 2.11.17.3.4. Ethernet 25G x 4 (FEC Off) 2.11.17.3.5. 10G/25G Ethernet Channel with Basic PTP Accuracy Mode 2.11.17.3.6. 10G/25G Ethernet Channel with Advanced PTP Accuracy Mode 2.11.17.3.7. 100G Ethernet with Aggregated FEC 2.11.17.3.8. 100G Ethernet with PTP 2.11.17.3.9. Single 25G Synchronous Ethernet Channel 2.11.17.3.10. Multiple 25G Synchronous Ethernet Channels
2.12. Register Descriptions x
2.12.1. Auto Negotiation and Link Training Registers 2.12.2. PHY Registers 2.12.3. TX MAC Registers 2.12.4. RX MAC Registers 2.12.5. Pause and Priority- Based Flow Control Registers 2.12.6. TX Statistics Counter Registers 2.12.7. RX Statistics Counter Registers 2.12.8. 1588 PTP Registers 2.12.9. RS-FEC Registers 2.12.10. PMA Registers
2.12.1. Auto Negotiation and Link Training Registers x
2.12.1.1. ANLT Sequencer Config 2.12.1.2. ANLT Sequencer Status 2.12.1.3. Auto Negotiation Config Register 1 2.12.1.4. Auto Negotiation Config Register 2 2.12.1.5. Auto Negotiation Status Register 2.12.1.6. Auto Negotiation Config Register 3 2.12.1.7. Auto Negotiation Config Register 4 2.12.1.8. Auto Negotiation Config Register 5 2.12.1.9. Auto Negotiation Config Register 6 2.12.1.10. Auto Negotiation Status Register 1 2.12.1.11. Auto Negotiation Status Register 2 2.12.1.12. Auto Negotiation Status Register 3 2.12.1.13. Auto Negotiation Status Register 4 2.12.1.14. Auto Negotiation Status Register 5 2.12.1.15. AN Channel Override 2.12.1.16. Consortium Next Page Override 2.12.1.17. Consortium Next Page Link Partner Status 2.12.1.18. Link Training Config Register 1 2.12.1.19. Link Training Status Register 1 2.12.1.20. Link Training Config Register for Lane 0 2.12.1.21. Link Training Config Register for Lane 1 2.12.1.22. Link Training Config Register for Lane 2 2.12.1.23. Link Training Config Register for Lane 3
2.12.2. PHY Registers x
2.12.2.1. PHY Module Revision ID 2.12.2.2. PHY Scratch Register 2.12.2.3. Loopback Mode 2.12.2.4. PHY Configuration 2.12.2.5. Reset Sequencer RS-FEC Disable 2.12.2.6. RX CDR PLL Locked 2.12.2.7. TX Datapath Ready 2.12.2.8. Frame Errors Detected 2.12.2.9. Clear Frame Errors 2.12.2.10. RX PCS Status for AN/LT 2.12.2.11. PCS Error Injection 2.12.2.12. Alignment Marker Lock 2.12.2.13. Change in RX PCS Deskew Status 2.12.2.14. BER Count 2.12.2.15. Transfer Ready (AIB reset) Status for EHIP, ELANE, and PTP Channels 2.12.2.16. EHIP, ELANE, and RS-FEC Reset Status 2.12.2.17. PCS Virtual Lane 0 2.12.2.18. PCS Virtual Lane 1 2.12.2.19. PCS Virtual Lane 2 2.12.2.20. PCS Virtual Lane 3 2.12.2.21. Recovered Clock Frequency in KHz 2.12.2.22. TX Clock Frequency in KHz 2.12.2.23. Configuration Fields for TX PLD 2.12.2.24. Status for TX PLDs 2.12.2.25. Status for Dynamic Deskew Buffer 2.12.2.26. Configuration for RX PLD Block 2.12.2.27. Configuration for RX PCS 2.12.2.28. BIP Counter 0 2.12.2.29. BIP Counter 1 2.12.2.30. BIP Counter 2 2.12.2.31. BIP Counter 3 2.12.2.32. BIP Counter 4 2.12.2.33. BIP Counter 5 2.12.2.34. BIP Counter 6 2.12.2.35. BIP Counter 7 2.12.2.36. BIP Counter 8 2.12.2.37. BIP Counter 9 2.12.2.38. BIP Counter 10 2.12.2.39. BIP Counter 11 2.12.2.40. BIP Counter 12 2.12.2.41. BIP Counter 13 2.12.2.42. BIP Counter 14 2.12.2.43. BIP Counter 15 2.12.2.44. BIP Counter 16 2.12.2.45. BIP Counter 17 2.12.2.46. BIP Counter 18 2.12.2.47. BIP Counter 19 2.12.2.48. Timer Window for Hi-BER Checks 2.12.2.49. Hi-BER Frame Errors 2.12.2.50. Error Block Count 2.12.2.51. Deskew Depth 0 2.12.2.52. Deskew Depth 1 2.12.2.53. Deskew Depth 2 2.12.2.54. Deskew Depth 3 2.12.2.55. RX PCS Test Error Count
2.12.3. TX MAC Registers x
2.12.3.1. TX MAC Module Revision ID 2.12.3.2. TX MAC Scratch Register 2.12.3.3. Link Fault Configuration 2.12.3.4. IPG Words to remove per Alignment Marker Period 2.12.3.5. Maximum TX Frame Size 2.12.3.6. TX MAC Configuration 2.12.3.7. EHIP TX MAC Feature Configuration 2.12.3.8. TX MAC Source Address Lower Bytes 2.12.3.9. TX MAC Source Address Higher Bytes
2.12.4. RX MAC Registers x
2.12.4.1. RX MAC Module Revision ID 2.12.4.2. RX MAC Scratch Register 2.12.4.3. Maximum RX Frame Size 2.12.4.4. RX CRC Forwarding 2.12.4.5. Link Fault Status 2.12.4.6. RX MAC Configuration 2.12.4.7. EHIP RX MAC Feature Configuration
2.12.5. Pause and Priority- Based Flow Control Registers x
2.12.5.1. TXSFC Module Revision ID 2.12.5.2. TX SFC Scratch Register 2.12.5.3. Enable TX Pause Ports 2.12.5.4. TX Pause Request 2.12.5.5. Enable Automatic TX Pause Retransmission 2.12.5.6. Retransmit Holdoff Quanta 2.12.5.7. Retransmit Pause Quanta 2.12.5.8. Enable TX XOFF 2.12.5.9. Enable Uniform Holdoff 2.12.5.10. Set Uniform Holdoff 2.12.5.11. Lower 4 bytes of the Destination address for Flow Control 2.12.5.12. Higher 2 bytes of the Destination address for Flow Control 2.12.5.13. Lower 4 bytes of the Source address for Flow Control frames 2.12.5.14. Higher 2 bytes of the Source address for Flow Control frames 2.12.5.15. TX Flow Control Feature Configuration 2.12.5.16. Pause Quanta 0 2.12.5.17. Pause Quanta 1 2.12.5.18. Pause Quanta 2 2.12.5.19. Pause Quanta 3 2.12.5.20. Pause Quanta 4 2.12.5.21. Pause Quanta 5 2.12.5.22. Pause Quanta 6 2.12.5.23. Pause Quanta 7 2.12.5.24. PFC Holdoff Quanta 0 2.12.5.25. PFC Holdoff Quanta 1 2.12.5.26. PFC Holdoff Quanta 2 2.12.5.27. PFC Holdoff Quanta 3 2.12.5.28. PFC Holdoff Quanta 4 2.12.5.29. PFC Holdoff Quanta 5 2.12.5.30. PFC Holdoff Quanta 6 2.12.5.31. PFC Holdoff Quanta 7 2.12.5.32. RXSFC Module Revision ID 2.12.5.33. RXSFC Scratch Register 2.12.5.34. Enable RX Pause Frame Processing 2.12.5.35. Forward Flow Control Frames 2.12.5.36. Lower 4 bytes of the Destination address for RX Pause Frames 2.12.5.37. Higher 2 bytes of the Destination address for RX Pause Frames 2.12.5.38. RX Flow Control Feature Configuration
2.12.6. TX Statistics Counter Registers x
2.12.6.1. TX Statistics Registers
2.12.7. RX Statistics Counter Registers x
2.12.7.1. RX Statistics Registers
3. About the E-Tile CPRI PHY Intel® FPGA IP x
3.1. Supported Features 3.2. E-Tile CPRI PHY Intel® FPGA IP Overview 3.3. E-Tile CPRI PHY Device Family Support 3.4. Resource Utilization 3.5. Release Information 3.6. E-Tile CPRI PHY Intel FPGA IP Core Device Speed Grade Support 3.7. Getting Started 3.8. Parameter Settings 3.9. Functional Description 3.10. E-Tile CPRI PHY Intel FPGA IP Interface Signals 3.11. Registers 3.12. Document Revision History for the E-Tile CPRI PHY Intel FPGA IP
3.7. Getting Started x
3.7.1. Installing and Licensing Intel® FPGA IP Cores 3.7.2. Specifying the IP Core Parameters and Options 3.7.3. Generated File Structure 3.7.4. E-Tile CPRI PHY Intel FPGA IP Channel Placement 3.7.5. IP Core Testbenches 3.7.6. Compiling the Full Design
3.7.1. Installing and Licensing Intel® FPGA IP Cores x
3.7.1.1. Intel® FPGA IP Evaluation Mode
3.7.4. E-Tile CPRI PHY Intel FPGA IP Channel Placement x
3.7.4.1. One 24.33024 Gbps channel with RS-FEC 3.7.4.2. Two 24.33024 Gbps Channel with RS-FEC 3.7.4.3. Three 24.33024 Gbps channels with RS-FEC 3.7.4.4. Four 24.33024 Gbps channels with RS-FEC 3.7.4.5. Restrictions
3.9. Functional Description x
3.9.1. CPRI PHY Functional Blocks 3.9.2. Dynamic Reconfiguration
3.9.1. CPRI PHY Functional Blocks x
3.9.1.1. E-Tile Native PHY 3.9.1.2. Soft Reset Sequencer 3.9.1.3. Latency Measurement
3.9.1.3. Latency Measurement x
3.9.1.3.1. Deterministic Latency Calculation
3.10. E-Tile CPRI PHY Intel FPGA IP Interface Signals x
3.10.1. Clock Signals 3.10.2. TX MII Interface 3.10.3. RX MII Interface 3.10.4. TX 8B/10B Interface 3.10.5. RX 8B/10B Interface 3.10.6. Status Interface for 64B/66B Line Rate 3.10.7. Status Interface for 8B/10B Line Rate 3.10.8. Serial I/O Pins 3.10.9. Reconfiguration Interfaces ( Avalon® Memory-Mapped Interface)
3.10.9. Reconfiguration Interfaces ( Avalon® Memory-Mapped Interface) x
3.10.9.1. CPRI PHY Reconfiguration Interface 3.10.9.2. Transceiver Reconfiguration Interface 3.10.9.3. RS-FEC Reconfiguration Interface
3.11. Registers x
3.11.1. PHY Registers 3.11.2. CPRI PHY Registers 3.11.3. PMA Registers 3.11.4. RS-FEC Registers
3.11.3. PMA Registers x
3.11.3.1. Minimizing PMA Adaptation Time
4. Supported Tools x
4.1. E-Tile Channel Placement Tool 4.2. Ethernet Toolkit Overview 4.3. Document Revision History for the E-Tile Channel Placement Tool and the Ethernet Link Inspector
4.2. Ethernet Toolkit Overview x
4.2.1. Features
1. About E-Tile Hard IP User Guide
2. About the E-Tile Hard IP for Ethernet Intel® FPGA IP Core
3. About the E-Tile CPRI PHY Intel® FPGA IP
4. Supported Tools
5. E-Tile Hard IP User Guide Archives

2.9.2.7. 10G/25G TX and RX Unit Interval Adjustment

The accuracy drift occurs when there is a PPM difference between the MAC layer clock and the Master TOD clock. To correct the drift, you may use the RX and TX Unit Interval (UI) adjustment method. IEEE 802.3 standards permit the Ethernet clocks frequency to vary within ±100 PPM.

For the system with PPM, you are required to do at least one UI adjustment once out of reset. Any timestamp before the UI adjustment is invalid. The UI adjustment shall be performed after the rx/tx_ptp_ready is asserted and before starting any PTP operation. The UI adjustment applies to the system independent of PPM provided that the PPM is within the Ethernet specification. Once UI adjustment is completed, it takes two Alignment marker periods for UI to adjust and produce an accurate timestamp.

The UI adjustment is a software flow, implemented by user software, utilizing 10G/25G PTP PPM UI Adjustment registers in the 1588 PTP Registers section to compute the new UI. Once determined, the UI register updates the UI value.

10G/25G UI Adjustment Calculation

The UI Adjustment Calculation applies to both, TX and RX paths. The software must take at least two snapshots of the 10G/25G PTP PPM UI Adjustment registers within 1s time frame. The new UI value is computed from the difference between the two snapshots. The longer the interval between the first and the next snapshot, the better accuracy the new UI value provides. 8 The accuracy can also be improved by taking multiple snapshots within 1s time frame. If two compared snapshots are taken outside of the 1s time frame, they shall be discarded.
Note: The UI adjustment shall not be performed when TOD changes are in progress or during reset.
User software performs the following steps to calculate the new UI value.
  1. Set TAM_SNAPSHOT to 1 to take the first snapshot of the Time of Alignment Marker (TAM) and the Alignment Marker Count (AM_Count) values. Your software snapshots the TAM and AM_Count values into the TX/RX_TAM_H/L and TX/RX_COUNT registers located in the 1588 PTP Registers.
  2. Read TX/RX_TAM_H/L and TX/RX_COUNT registers and save values from the first snapshot as:
    • TX_TAM_0 = {TX_TAM_H, TX_TAM_L}
    • TX_Count_0 = TX_COUNT
    • RX_TAM_0 = {RX_TAM_H, RX_TAM_L}
    • RX_Count_0 = RX_COUNT
  3. Clear TAM_SNAPSHOT to 0 to complete the first snapshot.
  4. Set TAM_SNAPSHOT to 1 again to take the Nth snapshot of the TAM and AM_Count values where N represents the number of taken snapshots.
  5. Read TX/RX_TAM_H/L and TX/RX_COUNT registers and save values from the Nth snapshot:
    • TX_TAM_N = {TX_TAM_H, TX_TAM_L}
    • TX_Count_N = TX_COUNT
    • RX_TAM_N = {RX_TAM_H, RX_TAM_L}
    • RX_Count_N = RX_COUNT
  6. Ensure the interval between the 1th snapshot and the Nth snapshot is within 1s else the snapshots are invalid for use and your software needs to restart from step 1.
  7. Calculate the new UI value:

    UI = TAM_Interval / (AM_Count * Reference_Time_Load_Interval).

    Refer steps below to calculate TAM_Interval, AM_Count, and est_AM_Count.

    Note: For more information about Reference Time Load Interval, refer to the Reference Time Load Interval.
  8. Compute the TAM_Interval value. TAM is a time value in nanosecond (ns). Once the TAM value reaches 1 billion ns, it rolls over to 1s creating a rollover condition. When TAM value rolls over, the subsequent TAM_N value appears smaller than the first TAM_0 value.
    • If (TAM_N > TAM_0): TAM_Interval (ns) = (TAM_N - TAM-_0)
    • If (TAM_N ≤ TAM_0): TAM_Interval (ns) = ((1s + TAM_N) - TAM_0)
    To calculate the TX_TAM_Interval, replace TAM_N with TX_TAM_N value and TAM_0 with TX_TAM_0 value. Same steps apply to calculate the RX_TAM_Interval.
  9. Calculate the estimated AM Count (est_AM_Count). The est_AM_Count value is used to ensure that AM_Count, calculated in next step, is valid.

    est_AM_Count = INT (TAM_Interval / (Reference_Time_Load_Interval * 0ppm_UI)

    where INT() is a round up function to the nearest integer, the value of 0ppm_UI for 10GE variant is 96.969696 ps and the value of 0ppm_UI for 25GE variant is 38.787878 ps. Compare the est_AM_Count with 64,000, which is the maximum AM_Count with offset. If est_AM_count exceeds 64,000, discard the snapshot and start from step 1.

  10. Calculate the AM_Count value. AM_Count can reach a rollover condition when reaching maximum value. Use the appropriate equation to calculate the AM_Count.
    • If (Count_N > Count_0): AM_Count = (Count_N – Count_0)
    • If (Count_N ≤ Count_0): AM_Count = ((65,535 – Count_0) + Count_N)
  11. Write the calculated TX and RX UI values to TX_UI_REG and RX_UI_REG registers.
Table 23.  Reference Time Load IntervalThis table shows the Reference time load interval values for PPM UI adjustment calculation.
Configuration Data Path Reference_Time_Load_Interval value in bits
25G variant with RS-FEC TX 81,920*66=5,406,720
Note: 81,920 is a 66-bit value of alignment marker interval (in terms of block numbers)
RX 81,920*66=5,406,720
10GE/25GE variants without RS-FEC TX 81,920*66=5,406,720
RX 6,336
100G with and without RS-FEC TX 16384*20*66=21,626,880
Note: 16384 is a 66-bit value of alignment marker interval (in terms of block numbers) per virtual lane.
RX
8 Comparing the first snapshot with a third snapshot taken at a later time gives a more accurate UI than comparing the first snapshot with the second snapshot taken at an earlier time.
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