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 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

2.9.2.12. 100G UI Adjustment

This section provides the steps to measure UI value to prevent time drift due to clock PPM as reference to golden Time-of-Day (ToD) in the platform.
Tip: Do not perform the measurement if there is a large adjustment to the ToD value, as it impacts the measurement result which is based on principle that the ToD value is incremented constantly based on golden ToD running at ideal clock with 0ppm.

TAM is reference time for Alignment Marker (AM) for variants with AM, and arbitrary selected reference bit for variants without AM.

  1. Request snapshot of initial TX TAM and RX TAM:
    csr_write (mlptp_tam_snapshot, 1’b1)
  2. Read snapshotted initial TAM and counter values:
    tx_tam_0_31_0 = csr_read (mlptp_tx_tam_l[31:0])
tx_tam_0_47_32 = csr_read (mlptp_tx_tam_h[15:0])
tx_tam_0_cnt = csr_read (mlptp_tx_am_count[15:0])

rx_tam_0_31_0 = csr_read (mlptp_rx_tam_l[31:0])
rx_tam_0_47_32 = csr_read (mlptp_rx_tam_h[15:0])
rx_tam_0_cnt = csr_read (mlptp_rx_am_count[15:0])

Form complete TAM by concatenation

tx_tam_0 = {tx_tam_0_47_32, tx_tam_0_31_0};
rx_tam_0 = {rx_tam_0_47_32, rx_tam_0_31_0};
  3. Clear snapshot:
    csr_write (mlptp_tam_snapshot, 1’b0)
  4. Starting from time when step 1 is executed, wait for time duration as specified in section Minimum and Maximum Reference Time (TAM) Interval for UI Measurement (Hardware).
  5. Request snapshot of Nth TX TAM and RX TAM:
    csr_write (mlptp_tam_snapshot, 1’b1)
  6. Read snapshotted Nth TAM and counter values:
    tx_tam_n_31_0 = csr_read (mlptp_tx_tam_l[31:0])
tx_tam_n_47_32 = csr_read (mlptp_tx_tam_h[15:0])
tx_tam_n_cnt = csr_read (mlptp_tx_am_count[15:0])

rx_tam_n_31_0 = csr_read (mlptp_rx_tam_l[31:0])
rx_tam_n_47_32 = csr_read (mlptp_rx_tam_h[15:0])
rx_tam_n_cnt = csr_read (mlptp_rx_am_count[15:0])

Form complete TAM by concatenation

tx_tam_n = {tx_tam_n_47_32, tx_tam_n_31_0};
rx_tam_n = {rx_tam_n_47_32, rx_tam_n_31_0};
  7. Clear snapshot:
    csr_write (mlptp_tam_snapshot, 1’b0)
  8. Calculation:
    1. Get TAM interval (tx_tam_interval and rx_tam_interval) from 10G/25G TX and RX Unit Interval Adjustment.
    2. Calculate time elapsed:
      tx_tam_delta = (tx_tam_n <= tx_tam_0) ? [(tx_tam_n + 10^9ns) – tx_tam_0] : (tx_tam_n – tx_tam_0)

rx_tam_delta = (rx_tam_n <= rx_tam_0) ? [(rx_tam_n + 10^9ns) – rx_tam_0] : (rx_tam_n – rx_tam_0)
      Note: 10^9ns = 48’h 3B9A_CA00_0000
    3. Calculate estimated count value:
      tx_tam_cnt_est	= round_up_to_nearest_integer(tx_tam_delta / (tx_tam_interval * 0ppm_UI))
rx_tam_cnt_est	= round_up_to_nearest_integer(rx_tam_delta / (rx_tam_interval * 0ppm_UI))

Where 0ppm_UI is 38.7878 ps.

If tx_tam_cnt_est or rx_tam_cnt_est > 64000, which indicates 16-bit counters may have already overflow 2 times or more, you must restart from step 1.

      This step is optional, and required only if snapshot may happen longer than duration specified in Minimum and Maximum Reference Time (TAM) Interval for UI Measurement (Hardware). For example: The read response of System-console via JTAG master is slow.

    4. Calculate TAM count value:
      tx_tam_cnt = (tx_tam_n_cnt < tx_tam_0_cnt) ? [(tx_tam_n_cnt + 2^16) – tx_tam_0_cnt] : (tx_tam_n_cnt – tx_tam_0_cnt)

rx_tam_cnt = (rx_tam_n_cnt < rx_tam_0_cnt) ? [(rx_tam_n_cnt + 2^16) – rx_tam_0_cnt] : (rx_tam_n_cnt – rx_tam_0_cnt)
    5. Calculate UI value:
      tx_ui = (tx_tam_delta) / (tx_tam_cnt * tx_tam_interval / 4)
rx_ui = (rx_tam_delta) / (rx_tam_ cnt * rx_tam_interval / 4) * 330
  9. Write the calculated UI value to IP:
    csr_write (mlptp_tx_ui, tx_ui)
csr_write (mlptp_rx_ui, rx_ui)

    Ensure the format is {4-bit nanoseconds, 24-bit fractional nanoseconds}.

  10. After first UI measurement, for every minimum TAM interval or longer duration, repeat step 1 to 9. This is to prevent time counter drift from golden Time-of-Day in the system whenever clock ppm changes.
Level Two Title