Texas Instruments TMS320C674X manual Emac Control Module, Internal Memory, Bus Arbiter, Cpu

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2.6EMAC Control Module

The EMAC control module (Figure 9) interfaces the EMAC and MDIO modules to the rest of the system, and also provides a local memory space to hold EMAC packet buffer descriptors. Local memory is used to help avoid contention with device memory spaces. Other functions include the bus arbiter, and interrupt logic control.

Figure 9. EMAC Control Module Block Diagram

Transmit and Receive DMA Controllers

Configuration bus

EMAC interrupts

MDIO interrupts

Arbiter and	CPU
bus switches

8K byte

descriptor memory

Configuration

registers

	Interrupts
Interrupt
logic	to CPU

2.6.1Internal Memory

The EMAC control module includes 8K bytes of internal memory (CPPI buffer descriptor memory). The internal memory block is essential for allowing the EMAC to operate more independently of the CPU. It also prevents memory underflow conditions when the EMAC issues read or write requests to descriptor memory. (Memory accesses to read or write the actual Ethernet packet data are protected by the EMAC's internal FIFOs).

A descriptor is a 16-byte memory structure that holds information about a single Ethernet packet buffer, which may contain a full or partial Ethernet packet. Thus with the 8K memory block provided for descriptor storage, the EMAC module can send and received up to a combined 512 packets before it needs to be serviced by application or driver software.

2.6.2Bus Arbiter

The EMAC control module bus arbiter operates transparently to the rest of the system. It is used:

•To arbitrate between the CPU and EMAC buses for access to internal descriptor memory.

•To arbitrate between internal EMAC buses for access to system memory.

SPRUFL5B –April 2011	EMAC/MDIO Module	29
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