Section 10: Ethernet Link Configuration; Overview; Gmii/Mii; Configuring The Ethernet Controller For Gmii And Mii Modes - Broadcom NetXtreme/NetLink BCM5718 Series Programmer's Manual

BCM5718 Programmer's Guide Ethernet Link Configuration
S e c t i o n 1 0 : E t h e r n e t L i n k C o n f i g u r a t i o n

Overview

The Ethernet controller supports multiple link operating modes. It can operate at multiple link speeds: 10 Mbps,
100 Mbps, or 1000 Mbps. It can also operate at half-duplex (IEE 802.3 CSMA/CD) or full-duplex. The MAC is
compliant with IEEE 802.3, IEEE 802.3u, IEEE 802.3x, and IEEE 802.3z specifications.

GMII/MII

The Gigabit Media Independent Interface (GMII) is normally used to interface the controller to a transceiver that
supports Gigabit Ethernet over copper wiring (1000BASE-T). The Media Independent Interface (MII) is used to
interface the controller to a transceiver that is capable of 10/100 Mbps Ethernet. Depending upon the link speed,
driver software will need to configure the Ethernet controller to operate in either GMII mode or MII mode.
Note: The integrated PHY transceiver of the BCM5718 has a has a fixed PHY address value of 1.

Configuring the Ethernet Controller for GMII and MII Modes

Configuring the Ethernet controller to operate in GMII or MII mode is simple. During initialization, software
should configure the Ethernet_MAC_Mode.Port_Mode bits to a value that corresponds to the correct interface
speed (01b for MII, 10b for GMII).
Configuring How MAC Detects Link Up/Down
The Ethernet controller has the ability to determine if the Ethernet link is up or down. The link will be down if the
Ethernet cable is not properly attached at both ends of the network. Link will be up only if the cable is properly
attached and the devices at both ends of the cable recognize that link has been established. The device cannot
successfully transfer packets on the link unless it determines that it has a valid link up.
The controller involves using the Ethernet controller's LNKRDY input signal. This method allows the Ethernet
controller to determine the link status based on the link status output from integrated PHY connected to
LNKRDY input of MAC. The Transmit_MAC_Status.Link Up bit (see "Transmit MAC Status Register (offset:
0x460)" on page 321) will reflect the link status input on LNKRDY signal to MAC from PHY. Host software can
enable this method by clearing the MII_Mode.Port_Polling bit (bit-4 of offset 0x454).
The link state of the Ethernet controller can also be forced by disabling both the auto-polling function and the
LNKRDY signal and forcing the link status by directly writing to the MII_Status.Link_Status bit.
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January 29, 2016 • 5718-PG108-R Page 203