Network Card User Manual

EMAC
control
module
Control
registers
and logic
PHY
monitoring
Peripheral
clock
MDIO
clock
generator
USERINT
MDIO
interface
polling
PHY
MDCLK
MDIO
LINKINT
Configuration bus
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2.8 MDIO Module
The MDIO module is used to manage up to 32 physical layer (PHY) devices connected to the Ethernet
Media Access Controller (EMAC). The DM36x device supports a single PHY being connected to the
EMAC at any given time. The MDIO module is designed to allow almost transparent operation of the
MDIO interface with little maintenance from the CPU.
The MDIO module continuously polls 32 MDIO addresses in order to enumerate all PHY devices in the
system. Once a PHY device has been detected, the MDIO module reads the MDIO PHY link status
register (LINK) to monitor the PHY link state. Link change events are stored in the MDIO module, which
can interrupt the CPU. This storing of the events allows the CPU to poll the link status of the PHY device
without continuously performing MDIO module accesses. However, when the CPU must access the MDIO
module for configuration and negotiation, the MDIO module performs the MDIO read or write operation
independent of the CPU. This independent operation allows the processor to poll for completion or
interrupt the CPU once the operation has completed.
2.8.1 MDIO Module Components
The MDIO module (Figure 9) interfaces to the PHY components through two MDIO pins (MDCLK and
MDIO), and to the CPU through the EMAC control module and the configuration bus. The MDIO module
consists of the following logical components:
• MDIO clock generator
• Global PHY detection and link state monitoring
• Active PHY monitoring
• PHY register user access
Figure 9. MDIO Module Block Diagram
2.8.1.1 MDIO Clock Generator
The MDIO clock generator controls the MDIO clock based on a divide-down of the peripheral clock
(PLL1/6) in the EMAC control module. The MDIO clock is specified to run up to 2.5 MHz, although typical
operation would be 1.0 MHz. Since the peripheral clock frequency is variable (PLL1/6), the application
software or driver controls the divide-down amount.
2.8.1.2 Global PHY Detection and Link State Monitoring
The MDIO module continuously polls all 32 MDIO addresses in order to enumerate the PHY devices in the
system. The module tracks whether or not a PHY on a particular address has responded, and whether or
not the PHY currently has a link. Using this information allows the software application to quickly
determine which MDIO address the PHY is using.
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SPRUFI5B–March 2009–Revised December 2010 Ethernet Media Access Controller (EMAC)/Management Data Input/Output
(MDIO)
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