SMSC LAN9311 Manual De Usuario

Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface

SMSC LAN9311/LAN9311i

97

Revision 1.4 (08-19-08)

 

The emulated auto-negotiation process is much simpler than the real process and can be categorized
into three steps:

1. Bit 5 (Auto-Negotiation Complete) is set in the 

2. Bit 1 (Page Received) is set in the 

.

3. The auto-negotiation result (speed and duplex) is determined and registered.

The auto-negotiation result (speed and duplex) is determined using the Highest Common Denominator
(HCD) of the 

 and 

specified in the IEEE 802.3 standard. The technology ability bits of these registers are ANDed, and if
there are multiple bits in common, the priority is determined as follows:

„

100Mbps Full Duplex (highest priority)

„

100Mbps Half Duplex

„

10Mbps Full Duplex 

„

10Mbps Half Duplex (lowest priority)

For example, if the full capabilities of the Virtual PHY are advertised (100Mbps, Full Duplex), and if
the link partner is capable of 10Mbps and 100Mbps, then auto-negotiation selects 100Mbps as the
highest performance mode. If the link partner is capable of half and full-duplex modes, then auto-
negotiation selects full-duplex as the highest performance operation. In the event that there are no bits
in common, an emulated 

 is used.

The 

 defaults to having all four

ability bits set. These values can be reconfigured via software. Once the auto-negotiation is complete,
any change to the 

 will not take

affect until the auto-negotiation process is re-run. The emulated link partner always advertises all four
abilities (100BASE-X full duplex, 100BASE-X half duplex, 10BASE-T full duplex, and 10BASE-T half
duplex) in the 

. Neither the Virtual PHY or the emulated link partner support next

page capability, remote faults, or 100BASE-T4.

If there is at least one common selection between the emulated link partner and the Virtual PHY
advertised abilities, then the auto-negotiation succeeds, the Link Partner Auto-Negotiation Able bit 0
of the 

 is set, and the technology

ability bits in the 

 are set to indicate the emulated link partners abilities.

For the Virtual PHY, the auto-negotiation register bits (and management of such) are used by
the Host MAC. So the perception of local and link partner is reversed. The local device is the
Host MAC, while the link partner is the switch fabric. This is consistent with the intention of the
Virtual PHY.

In the event that there are no common bits between the advertised ability and the emulated link
partners ability, auto-negotiation fails and emulated parallel detect is used. In this case, the Link
Partner Auto-Negotiation Able (bit 0) in the 

 will be cleared, and the communication set to 100Mbps half-duplex.  Only one of the

technology ability bits in the 

 will be set, indicating the emulated parallel detect result.

Auto-negotiation can be disabled in the Virtual PHY by clearing bit 12 (VPHY_AN) of the 

. The Virtual PHY will then force its speed of operation

to reflect the speed (bit 13) and duplex (bit 8) of the