Maxim DS33R11 specifications Half Duplex Flow Control, Host-Managed Flow Control

DS33R11 Ethernet Mapper with Integrated T1/E1/J1 Transceiver

Figure 9-3. Flow Control Using Pause Control Frame

Receive Queue

Growth

8

Rx

Data

Receive Queue Low

Water

Receive Queue High

Water Mark

Initiate Flow control

9.13.2 Half Duplex Flow Control

Half duplex flow control uses a jamming sequence to exert backpressure on the transmitting node. The receiving node jams the first 4 bytes of a packet that are received from the MAC in order to cause collisions at the distant end. In both 100Mbit/s and 10Mbit/s MII/RMII modes, 4 bytes are jammed upon reception of a new frame. Note that the jamming mechanism does not jam the current frame that is being received during the watermark crossing, but will wait to jam the next frame after the SU.RQHT bit is set. If the queue remains above the high threshold, received frames will continue to be jammed. This jam sequence is stopped when the queue falls below the high threshold.

9.13.3 Host-Managed Flow Control

Although automatic flow control is recommended, flow control by the host processor is also possible. By utilizing the high watermark interrupts, the host processor can manually issue pause frames or jam incoming packets to exert backpressure on the transmitting node. Pause frames can be initiated with SU.MACFCR.FCB bit. Jam sequences can be initiated be setting SU.GCR.JAME. The host can detect pause frames by monitoring SU.RFSB3.UF and SU.RFSB3.CF. Jammed frames will be indistinguishable from packet collisions.

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