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

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Date 8/30/2022
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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 with PTP or with External AIB Clocking 2.9.10. 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-MM)
3.10.9. Reconfiguration Interfaces (Avalon-MM) 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

2.11.4. RX PCS Interface to User Logic

The E-Tile Hard IP for Ethernet Intel FPGA IP RX client interface in PCS Only variations employs the Media Independent Interface (MII) protocol.

The RX PCS acts as a source and the client acts as a sink in the receive direction.

Table 34.  Signals of the MII RX Client InterfaceAll interface signals are clocked by the RX clock. The signal names are standard Avalon® streaming interface signals with slight differences to indicate the variations. For example:
  • For variants with single 10GE/25GE channel: i_sl_rx_data
  • For variants with more than 1 channels: i_sl_rx_data[n-1:0]
  • For variants with single 100E channel:i_rx_data

Signal Name

Width

Description

i_sl_clk_rx

i_sl_clk_rx[n-1:0]

i_clk_rx

1 bit for each channel

The RX clock for the IP core that drives the channel.

o_sl_rx_mii_d

o_sl_rx_mii_d[n-1:0]

o_rx_mii_d

64 bits for each channel (10G/25G)

256 bits (100G)

RX MII data. Data is in MII encoding. o_rx_mii_d[7:0] holds the first byte the IP core received on the Ethernet link. o_rx_mii_d[0] holds the first bit the IP core received on the Ethernet link.

When RX MII valid signal has the value of 0 or the RX valid alignment marker signal has the value of 1, the value on this signal is invalid.

o_sl_rx_mii_c

o_sl_rx_mii_c[n-1:0]

o_rx_mii_c

8 bits for each channel (10G/25G)

32 bits (100G

RX MII control bits. Each bit corresponds to a byte of RX MII data. o_rx_mii_c[0] corresponds to o_rx_mii_d[7:0], o_rx_mii_c[1] corresponds to o_rx_mii_d[15:8], and so on.

If the value of a bit is 1, the corresponding data byte is a control byte. If the value of a bit is 0, the corresponding data byte is data.

The Start of Packet byte (0xFB), End of Packet byte (0xFD), Idle bytes (0x07), and error byte (0xFE) are control bytes, but the preamble bytes, Start of Frame (SFD) byte (0xD5), CRC bytes, and payload bytes are data bytes.

When RX MII valid signal has the value of 0 or the RX valid alignment marker signal has the value of 1, the value on this signal is invalid.

o_sl_rx_mii_valid

o_sl_rx_mii_valid[n-1:0]

o_rx_mii_valid

1 bit for each channel Indicates that the RX MII data, RX MII control bits, and the RX valid alignment marker signals are valid.

o_sl_rx_mii_am_valid

o_sl_rx_mii_am_valid[n-1:0]

o_rx_mii_am_valid

1 bit for each channel Indicates the IP core received a valid alignment marker on the Ethernet link.

When the RX MII valid signal has the value of 0, the value on this signal is invalid. The value of the RX MII valid signal may fall while the IP core is asserting this signal.

o_sl_rx_pcs_fully_aligned

o_sl_rx_pcs_fully_aligned[n-1:0]

o_rx_pcs_fully_aligned

1 bit for each channel Asserts when RX PCS is ready to receive data.
Figure 44. Receiving Data Using the PCS Mode RX Interface

The figure above shows how to read packets from the RX PCS using the PCS mode RX interface.

  • The packets are MII encoded.
    • Each byte in o_rx_mii_d has a corresponding bit in o_rx_mii_c that indicates whether the byte is a control byte or a data byte; for example, o_rx_mii_c[2] is the control bit for o_rx_mii_d[23:16].
  • The data is only valid when o_rx_mii_valid is high. The contents of the o_rx_mii_d and o_rx_mii_c buses are not defined when o_rx_mii_valid is low.
  • The byte order for the PCS mode RX interface is opposite of the byte order for the MAC client. Bytes flow from right to left; the first byte that the core receives is o_rx_mii_d[7:0].
  • The bit order for the PCS mode RX interface is the same as the bit order of the MAC client. The first bit that the core receives is o_rx_mii_d[0].
Note: The PCS mode RX interface is not SOP aligned. New packets can begin on any byte position that is divisible by 8 (PCS data is transferred in 8-byte blocks).
Table 35.  Reading a Start Packet Block with Preamble from a PCS Mode TX Interface
MII Data MII Control Ethernet Packet Byte
o_rx_mii_d[7:0] 0xFB o_rx_mii_c[0] 1 Start of Packet
o_rx_mii_d[15:8] 0x55 o_rx_mii_c[1] 0 Preamble
o_rx_mii_d[23:16] 0x55 o_rx_mii_c[2] 0 Preamble
o_rx_mii_d[31:24] 0x55 o_rx_mii_c[3] 0 Preamble
o_rx_mii_d[39:32] 0x55 o_rx_mii_c[4] 0 Preamble
o_rx_mii_d[47:40] 0x55 o_rx_mii_c[5] 0 Preamble
o_rx_mii_d[55:48] 0x55 o_rx_mii_c[6] 0 Preamble
o_rx_mii_d[63:56] 0xD5 o_rx_mii_c[7] 0 SFD
Figure 45. Receiving Alignment Markers

o_rx_mii_am_valid indicates the arrival of the alignment markers from the RX PCS. The alignment markers also depend on o_rx_mii_valid. When o_rx_mii_valid is low, o_rx_mii_am_valid is not valid.

The contents of the o_rx_mii_d and o_rx_mii_c buses are not defined when o_rx_mii_valid is low. This is because alignment markers are not part of the 64b/66b encoding, and do not have an MII equivalent.

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