IP-10GETHERNET Altera, IP-10GETHERNET Datasheet - Page 51

• Manufacturer Part Number: IP-10GETHERNET
• Description: IP CORE - 10 Gbps Ethernet MAC PCS PMA Reference Design
• Manufacturer: Altera

Specifications of IP-10GETHERNET

• Software Application: IP CORE, Interface And Protocols, ETHERNET
• Supported Families: Quartus II
• Core Architecture: FPGA
• Core Sub-architecture: Stratix
• Rohs Compliant: NA
• Lead Free Status / RoHS Status: na

Congestion and Flow Control Using Pause Frames
3.4. Congestion and Flow Control Using Pause Frames
Figure 3–22. The XOFF and XONN Pause Frames
3.4.1. Conditions Triggering XOFF Frame Transmission
© July 2010 Altera Corporation
Note to
(1) One pause quanta fraction is equivalent to 512 bit times, which equates to 512/64 (the width of the MAC data bus), or 8 cycles for the system
(2) The bytes P1 and P2 are filled with the value configured in the pause_quant register.
DESTINATION ADDRESS[47:0] = 0x010000C28001
clock.
PAUSE QUANTA[15:0] = 0xP1, 0xP2
Figure
OPCODE[15:0] - 0X0001
3–22:
SOURCE ADDR[47:0]
TYPE[15:0] 0x0808
PREAMBLE[47:0]
XOFF Frame
START[7:0]
PAD[355:0]
CRC[31:0]
SFD[7:0]
The 10-Gbps Ethernet MAC provides flow control to control congestion at the local or
remote link partner. When either link partner devices experience congestion, the
respective transmit control sends pause frames. The pause frame instructs the remote
transmitter to stop sending data for the duration specified by the congested receiver.
When a device receives the XOFF pause control frame, it stops transmitting frames to
the link partner for a period equal to the pause quanta of the incoming pause frame.
The pause quanta can be configured in the pause quanta register of the device
sending XOFF frames. If the pause frame is received in the middle of a frame
transmission, the transmitter finishes sending the current frame and then suspends
transmission for a period specified by the pause quanta. Data transmission resumes
when a pause frame with quanta of zero is received or when the timer has expired.
The pause quanta received overrides any counter currently stored. When more than
one pause quanta is sent, the value of the pause is set to the last quanta received.
XOFF pause frames stop the remote transmitter. XON pause frames let remote
transmitter resume data transmission.
The Tx MAC transmits XOFF frames when one of the following conditions occurs:
■
Local device congestion (Rx FIFO almost full on)—When the local Rx FIFO asserts
the rx_almost_full flag, XOFF pause frames are sent to the remote device.
Setting the config register bit NO_PAUSE_FIFO disables this behavior. This feature
is only available if you choose to include the optional FIFO in your design.
1
If you use this mode be sure to size the FIFO to meet the IEEE 802.3 latency
requirements.
(2)
(Note 1)
Figure 3–22
DESTINATION ADDRESS[47:0] = 0x010000C28001
PAUSE QUANTA[15:0] = 0x00000000
OPCODE[15:0] - 0X0001
illustrates these frames.
SOURCE ADDR[47:0]
TYPE[15:0] 0x0808
PREAMBLE[47:0]
10-Gbps Ethernet IP Functional Description
START[7:0]
PAD[355:0]
XON Frame
CRC[31:0]
SFD[7:0]
3–25