Altera 10-Gbps Ethernet MAC MegaCore Function - Manual (Page 72)

Chapter 7: Functional Description 7–5
Frame Types
February 2014 Altera Corporation 10-Gbps Ethernet MAC MegaCore Function User Guide
7.3. Frame Types
The MAC supports the following frame types:
■ Basic Ethernet frames, including jumbo frames.
■ VLAN and stacked VLAN frames.
■ Control frames, which include pause and PFC frames.
f Refer to Appendix A, Frame Format for the frame formats and fields.
7.4. Transmit Datapath
The MAC TX receives the client payload data with the destination and source
addresses, and appends various control fields. Depending on the MAC configuration,
the MAC TX could perform the following tasks: pads the payload to satisfy the
minimum Ethernet frame payload of 64 bytes, calculates and appends the CRC-32
field, modifies the source address, inserts inter-packet gap bytes, and accepts
client-defined preamble bytes.
To perform these tasks, the MAC TX deasserts the avalon_st_tx_ready signal during
the frame transfer.
Figure 7–4 shows the typical flow of frame through the MAC TX.
7.4.1. Frame Payload Padding
The MAC TX inserts pad bytes (0x00) into transmit frames when the payload length
doesn't meet the minimum length required:
■ 46 bytes for basic frames
■ 42 bytes for VLAN tagged frames
■ 38 bytes for stacked VLAN tagged frames
Figure 7–4. Typical Client Frame at Transmit Interface
Notes to Figure 7–4 :
(1) <p> = payload size = 0–1500 bytes
(2) <s> = padding bytes = 0–46 bytes
(3) <I> = number of IPG bytes
Client - MAC Tx Interface
(optional)
Client Frame
MAC Frame
Destination
Addr[47:0]
Source
Addr[47:0]
Type/
Length[15:0]
Payload
[:0]
Destination
Addr[47:0]
SFD[7:0]
Preamble
[55:0]
CRC32
[31:0]
PAD []
Source
Addr[47:0]
Client-Defined Preamble
[63:0]
(optional)
Type/
Length[15:0]
Payload
[:0]
PAD []
CRC32
[31:0]
EFD[7:0]
IPG
[:0]
Frame Length
(1) (2)
(3)