Broadcom BCM5722 Programmer's Manual page 211

Programmer's Guide
10/15/07
S e c t i on 1 0 : E t he r n e t Li n k C on f i gu r a ti o n
O
VERVIEW
The BCM5722 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 BCM5722 Ethernet controller to operate in either GMII mode or MII mode.
Note: The integrated PHY transceiver of BCM5722 Ethernet controllers is hardcoded with a PHY address of 1.
C BCM5722 E
ONFIGURING THE
Configuring the BCM5722 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).
C H
ONFIGURING OW
The BCM5722 Ethernet controller has two different methods that it can use 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 first method is called auto-polling. Software can enable auto-polling by setting the MI_Mode.Port_Polling bit. If enabled,
the BCM5722 Ethernet controller periodically generates MDIO cycles to read the PHY's Link_Status bit in MII Status register
(see "MI Status Register (Offset 0x450)" on page
MI_Status_Register.Link_Status and Transmit_MAC_Status.Link_Up (see
on page 253) bits.
The second method involves using the BCM5722 Ethernet controller's LNKRDY input signal. This method allows the
BCM5722 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
page 253) will reflect the link status input on LNKRDY signal to MAC from PHY. Host software can enable this method by
clearing the MI_Mode.Port_Polling bit (bit-4 of offset 0x454).
The link state of the BCM5722 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 MI_Status.Link_Status bit.
Document 5722-PG101-R
THERNET CONTROLLER FOR
MAC D L
ETECTS INK
251). The link status from the auto-polling operation is then reported in the
Bro adco m Co rp or atio n
GMII
U /D
P OWN
"Transmit MAC Status Register (Offset 0x460)"
"Transmit MAC Status Register (Offset 0x460)" on
BCM5722
MII M
AND ODES
Ethernet Link Configuration Page 152