Texas Instruments TMS320DM646x manual Mdio Module Components, Mdio Clock Generator

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Architecture

If the rate of transmit pulse interrupt inputs is much less than the target transmit pulse interrupt rate specified in CMTXINTMAX, then the interrupts are not blocked to the CPU. If the transmit pulse interrupt rate is greater than the specified target rate in CMTXINTMAX, the interrupt is paced at the rate specified in this register, which should be written with a value between 2 and 63 inclusive, indicating the target number of interrupts per 1 ms going to the CPU. Similarly, the number of receive interrupt pulses to the CPU is also separately controlled.

2.7MDIO Module

The MDIO module is used to manage up to 32 physical layer (PHY) devices connected to the Ethernet Media Access Controller (EMAC). The DM646x 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.

2.7.1MDIO Module Components

The MDIO module (Figure 10) 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 10. MDIO Module Block Diagram
Peripheral	MDIO
clock
	clock
	generator	MDIO
USERINT
		interface
EMAC
control
module
LINKINT	PHY	PHY
	monitoring	polling
	Control
Configuration bus	registers
	and logic

MDCLK

MDIO

2.7.1.1MDIO 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.

34 Ethernet Media Access Controller (EMAC)/Management Data Input/Output (MDIO) SPRUEQ6–December 2007

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