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Architecture
2.6 EMAC 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
2.6.1 Internal 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.
2.6.2 Bus 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.
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SPRUFL5B–April 2011 EMAC/MDIO Module
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