Texas Instruments TMS320C674X Transmit DMA Engine, Transmit FIFO, MAC Transmitter, State RAM

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2.8.1.4Transmit DMA Engine

The transmit DMA engine is the interface between the transmit FIFO and the CPU. It interfaces to the CPU through the bus arbiter in the EMAC control module.

2.8.1.5Transmit FIFO

The transmit FIFO consists of three cells of 64-bytes each and associated control logic. The FIFO buffers data in preparation for transmission.

2.8.1.6MAC Transmitter

The MAC transmitter formats frame data from the transmit FIFO and transmits the data using the CSMA/CD access protocol. The frame CRC can be automatically appended, if required. The MAC transmitter also detects transmission errors and passes statistics to the statistics registers.

2.8.1.7Statistics Logic

The Ethernet statistics are counted and stored in the statistics logic RAM. This statistics RAM keeps track of 36 different Ethernet packet statistics.

2.8.1.8State RAM

State RAM contains the head descriptor pointers and completion pointers registers for both transmit and receive channels.

2.8.1.9EMAC Interrupt Controller

The interrupt controller contains the interrupt related registers and logic. The 26 raw EMAC interrupts are input to this submodule and masked module interrupts are output.

2.8.1.10Control Registers and Logic

The EMAC is controlled by a set of memory-mapped registers. The control logic also signals transmit, receive, and status related interrupts to the CPU through the EMAC control module.

2.8.1.11Clock and Reset Logic

The clock and reset submodule generates all the EMAC clocks and resets. For more details on reset capabilities, see Section 2.14.1.

2.8.2EMAC Module Operational Overview

After reset, initialization, and configuration, the host may initiate transmit operations. Transmit operations are initiated by host writes to the appropriate transmit channel head descriptor pointer contained in the state RAM block. The transmit DMA controller then fetches the first packet in the packet chain from memory. The DMA controller writes the packet into the transmit FIFO in bursts of 64-byte cells. When the threshold number of cells, configurable using the TXCELLTHRESH bit in the FIFO control register (FIFOCONTROL), have been written to the transmit FIFO, or a complete packet, whichever is smaller, the MAC transmitter then initiates the packet transmission. The SYNC block transmits the packet over the MII or RMII interfaces in accordance with the 802.3 protocol. Transmit statistics are counted by the statistics block.

Receive operations are initiated by host writes to the appropriate receive channel head descriptor pointer after host initialization and configuration. The SYNC submodule receives packets and strips off the Ethernet related protocol. The packet data is input to the MAC receiver, which checks for address match and processes errors. Accepted packets are then written to the receive FIFO in bursts of 64-byte cells. The receive DMA controller then writes the packet data to memory. Receive statistics are counted by the statistics block.

36	EMAC/MDIO Module	SPRUFL5B –April 2011
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