Altera Triple Speed Ethernet MegaCore Function User Manual Page 43
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The backoff time is a multiple of slot times. One slot is equal to a 512 bit times period. The number of the
delay slot times, before the Nth retransmission attempt, is chosen as a uniformly distributed random integer
in the following range:
0 ≤ r < 2k
k = min(n, N), where n is the number of retransmissions and N = 10.
For example, after the first collision, the backoff period, in slot time, is 0 or 1. If a collision occurs during
the first retransmission, the backoff period, in slot time, is 0, 1, 2, or 3.
The maximum backoff time, in 512 bit times slots, is limited by N set to 10 as specified in the IEEE Standard
802.3.
If collision occurs after 16 consecutive retransmissions, the MAC function reports an excessive collision
condition by setting the EXCESS_COL bit in the command_config register to 1, and discards the current frame
from the transmit FIFO buffer.
In networks that violate standard requirements, collision may occur after the transmission of the first 64
bytes. If this happens, the MAC function stops transmitting the current frame, discards the rest of the frame
from the transmit FIFO buffer, and resumes transmitting the next available frame.
MAC Receive Datapath
The MAC function receives Ethernet frames from the network via a PHY and forwards the payload with
relevant frame fields to the user application after performing checks, filtering invalid frames, and removing
the preamble and SFD.
Preamble Processing
The MAC function uses the SFD (0xD5) to identify the last byte of the preamble. If an SFD is not found after
the seventh byte, the MAC function rejects the frame and discards it.
The IEEE standard specifies that frames must be separated by an interpacket gap (IPG) of at least 96 bit
times. The MAC function, however, can accept frames with an IPG of less than 96 bit times; at least 8-bytes
and 6-bytes in RGMII/GMII (1000 Mbps operation) and RGMII/MII (10/100 Mbps operation) respectively.
The MAC function removes the preamble and SFD fields from valid frames.
Collision Detection in Half-Duplex Mode
In half-duplex mode, the MAC function checks for collisions during frame reception. When collision is
detected during the reception of the first 64 bytes, the MAC function discards the frame if the RX_ERR_DISC
bit is set to 1. Otherwise, the MAC function forwards the frame to the user application with error.
Address Checking
The MAC function can accept frames with the following address types:
• Unicast address—bit 0 of the destination address is 0.
• Multicast address—bit 0 of the destination address is 1.
• Broadcast address—all 48 bits of the destination address are 1.
The MAC function always accepts broadcast frames. If promiscuous mode is enabled (PROMIS_EN bit in
the command_config register = 1), the MAC function omits address filtering and accepts all frames.
Altera Corporation
Functional Description
Send Feedback
4-7
MAC Receive Datapath
UG-01008
2014.06.30
- User Guide 1
- Contents 2
- Altera Corporation 10
- About This MegaCore Function 10
- Send Feedback 10
- High-Level Block Diagrams 10
- Figure 1-2: Multi-port MAC 11
- 10/100/1000-Mbps 12
- Ethernet MAC 12
- Optical Platform 14
- Copper Platform 14
- Release Information 18
- DescriptionItem 19
- Using the Parameter Editor 24
- Design Walkthrough 25
- Simulate the System 27
- Programming an FPGA Device 27
- Generated Files 28
- DescriptionFile Name 29
- Quartus II Pin 29
- Assignment 29
- Parameter Settings 30
- Ethernet MAC Options 31
- FIFO Options 33
- Timestamp Options 34
- PCS/Transceiver Options 34
- ParameterValueName 35
- Functional Description 37
- MAC Architecture 38
- MAC Interfaces 39
- MAC Transmit Datapath 40
- IP Payload Re-alignment 41
- Address Insertion 41
- Frame Payload Padding 41
- CRC-32 Generation 41
- Interpacket Gap Insertion 42
- MAC Receive Datapath 43
- ValueHash Code Bit 44
- Frame Type Validation 45
- Payload Pad Removal 46
- CRC Checking 46
- Length Checking 46
- Frame Writing 47
- IP Payload Alignment 47
- FIFO Buffer Thresholds 48
- Receive Thresholds 49
- Transmit Thresholds 51
- Congestion and Flow Control 52
- Magic Packets 53
- MAC Local Loopback 54
- MAC Error Correction Code 55
- MAC Reset 55
- PHY Management (MDIO) 56
- MDIO Connection 57
- MDIO Frame Format 57
- Gigabit Ethernet 58
- Programmable 10/100 Ethernet 59
- Transmit Operation 62
- Receive Operation 63
- SGMII Converter 64
- Auto-Negotiation 65
- SGMII Auto-Negotiation 66
- Ten-bit Interface 68
- PHY Loopback 69
- PHY Power-Down 69
- POWERDOWN 70
- 1000BASE-X PCS 70
- IEEE 1588v2 Features 72
- Time of Day 73
- IEEE 1588v2 Receive Datapath 74
- IEEE 1588v2 Frame Format 74
- 0..1500/9600 Octets 75
- 4 Octets 75
- CRC4 Octets 76
- 0..1500/9600 Octets Payload 76
- MAC Header 77
- UDP Header 77
- IP Header 77
- PTP Header 77
- Software Requirements 78
- Base Addresses 80
- IEEE 1588v2 Feature PMA Delay 100
- UG-01008 101
- 2014.06.30 101
- DescriptionR/WNameBit(s) 103
- DescriptionR/WNameBit 105
- 1000BASE-X 106
- Register Initialization 110
- Configuration Register Space 111
- Interface Signals 116
- Clock and Reset Signal 117
- MAC Control Interface Signals 118
- MAC Status Signals 118
- MAC Receive Interface Signals 119
- DescriptionBit 120
- DescriptionI/OName 123
- MII/GMII/RGMII Signals 124
- PHY Management Signals 125
- ECC Status Signals 126
- TBI Interface Signals 131
- Status LED Control Signals 132
- SERDES Control Signals 132
- Related Information 133
- SectionInterface Signal 135
- 1.25 Gbps Serial Interface 138
- Transceiver Native PHY Signal 138
- DescriptionWidthI/OSignal 141
- 1000BASE-X/SGMII PCS Signals 149
- PCS Control Interface Signals 150
- PCS Reset Signals 150
- SGMII Status Signals 152
- Avalon-ST Receive Interface 155
- IEEE 1588v2 Timestamp 162
- Design Considerations 163
- Configurations(1) 164
- Sharing Transceiver Quads 169
- Timing Constraints 171
- Recommended Clock Frequency 173
- 50–100CLK 174
- 1000BASE-X/SGMII PCS only 174
- 125REF_CLK 174
- 125TBI_TX_CLK 174
- 125TBI_RX_CLK 174
- Testbench 175
- Testbench Verification 176
- Testbench Configuration 177
- Test Flow 177
- Simulation Model 178
- Simulation Model Files 179
- Driver Architecture 180
- PHY Speed Bits 181
- Speed (Mbps) 181
- Using Jumbo Frames 183
- API Functions 184
- Constants 189
- DescriptionValueConstant 190
- Ethernet Frame Format 192
- Pause Frame Format 194
- Description 195
- XON_GENXOFF_GEN 195
- Simulation Parameters 196
- DefaultDescriptionParameter 197
- Test Configuration Parameters 198
- Time-of-Day (ToD) Clock 201
- ToD Clock Parameter Setting 202
- ToD Clock 203
- DescriptionR/WNameDword 205
- Adjusting ToD Clock Drift 206
- ToD Synchronizer 207
- ToD Synchronizer Block 208
- 32/6364/31516/6364/63Settings 209
- DescriptionValueName 209
- ToD Synchronizer Signals 210
- Packet Classifier 212
- Packet Classifier Signals 213
- Additional Information 217
- Document Revision History 218
- ChangesVersionDate 219
- How to Contact Altera 223
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