Intel IXF1104 manual 5.1.2.1802.3x Flow Control Full-DuplexOperation, Datasheet

IXF1104 Quad-Port 10/100/1000 Mbps Ethernet Media Access Controller

The IXF1104 MAC implements the IEEE 802.3x standard RX FIFO threshold-based Flow Control in copper and fiber modes. When appropriately programmed, the MAC can both generate and respond to IEEE standard pause frames in full-duplex operation. The IXF1104 also supports externally triggered flow control through the Transmit Pause Control interface.

In half-duplex operation, the MAC generates collisions instead of sending pause frames to manage the incoming traffic from the link partner

5.1.2.1802.3x Flow Control (Full-Duplex Operation)

The IEEE 802.3x standard identifies four options related to system flow control:

•No Pause

•Symmetric Pause (both directions)

•Asymmetric Pause (Receive direction only)

•Asymmetric Pause (Transmit direction only)

The IXF1104 supports all four options on a per-port basis. Bits 2:0 of the “FC Enable ($ Port_Index

+0x12)” on page 167 provide programmable control for enabling or disabling flow control in each direction independently.

The IEEE 802.3x flow control mechanism is accomplished within the MAC sublayer, and is based on RX FIFO thresholds called watermarks. The RX FIFO level rises and falls as packets are received and processed. When the RX FIFO reaches a watermark (either exceeding a High or dropping below a Low after exceeding a High), the IXF1104 control sublayer signals an internal state machine to transmit a PAUSE frame. The FIFOs automatically generate PAUSE frames (also called control frames) to initiate the following:

•Halt the link partner when the High watermark is reached.

•Restart the link partner when the data stored in the FIFO falls below the Low watermark.

Figure 7 illustrates the IEEE 802.3 FIFO flow control functions.

Datasheet 69

Document Number: 278757

Revision Number: 007

Revision Date: March 25, 2004