Altera 40-Gbps Ethernet MAC and PHY MegaCore Function - Manual (Page 51)

Figure 3-2: Typical Client Frame at the Transmit Interface
Illustrates the changes that the TX MAC makes to the client frame. This figure uses the following
notational conventions:
•
= payload size = 0–1500 bytes, or 9600 bytes for jumbo frames.
• = padding bytes = 0–46 bytes.
• = number of IPG bytes
MAC Frame
Added by MAC for TX packets
Destination
Addr[47:0]
SFD[7:0]
Preamble
[47:0]
CRC32
[31:0]
IPG
[:0]
PAD []
Source
Addr[47:0]
Type/
Length[15:0]
Payload
[:0]
Start EFD[7:0]
Added by MAC for TX packets Payload Data from Client
The following sections describe the functions that the TX module performs:
Preamble, Start, and SFD Insertion on page 3-4
Address Insertion on page 3-4
Length/Type Field Processing on page 3-5
Frame Padding on page 3-5
Frame Check Sequence (CRC-32) Insertion on page 3-5
Inter-Packet Gap Generation and Insertion on page 3-5
Preamble, Start, and SFD Insertion
In the TX datapath the MAC appends a one-byte Start, 6-byte preamble, and 1-byte SFD to the client
frame. This MAC module also incorporates the functions of the reconciliation sublayer. The source of the
6-byte preamble and 1-byte SFD depends on whether you turn on the TX preamble pass-through feature
by setting bit 1 of the
Preamble Pass-Through Configuration
register at offset 0x125.
If the TX preamble pass-through feature is turned on, the client provides the eight-byte preamble (Start
byte, 6-byte preamble, and 1-byte SFD) on the data bus. However, the IP core overwrites the Start byte the
client provides, and only passes on the 6-byte preamble and the SFD. The client is responsible for
providing an appropriate SFD byte.
Related Information
MAC Feature Configuration Registers on page 3-105
Includes information about the
Preamble Pass-Through Configuration
register.
Address Insertion
The client provides the destination MAC address and the source address of the local MAC. However, if
enabled by bit [31] of the
MADDR_CTRL
register at offset 0xC2, the source MAC address can be replaced by
the source address contained in two, 32-bit MAC registers:
SRC_AD_LO
and
SRC_AD_HI
.
3-4 Preamble, Start, and SFD Insertion
UG-01088
2014.12.15
Altera Corporation Functional Description
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