
110
Functional Operation
Chapter 3
AMD-8111 HyperTransport I/O Hub Data Sheet
24674
Rev. 3.00
April 2003
AMD Preliminary Information
3.10.11.3
MII Network Status Interface
The MII also provides the CRS (Carrier Sense) and COL (Collision Sense) signals that are required
for IEEE 802.3 operation. Carrier Sense is used to detect non-idle activity on the network for the
purpose of inter-frame spacing timing in half-duplex mode. Collision Sense is used to indicate that
simultaneous transmission has occurred in a half-duplex network.
3.10.11.4
MII Management Interface
The MII provides a two-wire management interface so that the network controller can control
external PHY devices and receive status from them.
The network controller offers direct hardware support of the external PHY device without software
intervention. The device automatically uses the MII Management Interface to read auto-negotiation
information from the external PHY device and configures the MAC accordingly. The controller also
provides the host CPU indirect access to the external PHY through the PHY Access Register.
With software support the network controller can support up to 31 external PHYs attached to the MII
Management Interface.
Two independent state machines use the MII Management Interface to poll external PHY devices: the
Network Port Manager and the Auto-poll State Machine. The Network Port Manager coordinates the
auto-negotiation process, while the Auto-poll State Machine interrupts the host CPU when it detects
changes in user-selected PHY registers.
The Network Port Manager sends a management frame to the default PHY about once every 600 ms
to determine auto-negotiation results and the current link status. The Network Port Manager uses the
auto-negotiation results to set the MAC's speed, duplex mode, and flow control ability. Changes
detected by the Network Port Manager affect the operation of the MAC and MIB counters. For
example, if link failure is detected, the transmitter increments the XmtLossCarrier counter each time
it attempts to transmit a frame.
The Auto-poll State Machine periodically sends management frames to poll the status register of the
default PHY device plus up to 5 user-selected PHY registers and interrupts the host processor if it
detects a change in any of these registers. The Auto-poll State Machine does not change the state of
the MAC engine.
3.10.11.5
MII Management Frames
The format of an MII Management Frame is defined in Clause 22 of IEEE standard 802.3. The start of
an MII Management Frame is a preamble of 32 ones that ensures that all of the external PHYs are
synchronized on the same interface. (See Figure 26 on page 111.) Loss of synchronization is possible
due to the
hot-plugging
capability of the exposed MII. The preamble can be suppressed as described
below if the external PHY is designed to accept frames with no preamble.