Ethernet MAC
UG0331 User Guide Revision 15.0
376
11.2.1.1 AHB Engine
The EMAC can be accessed from an AHB system bus using the AHB engine. The AHB engine module is
positioned between the AHB system bus and the
MAC TX and RX FIFO.
The AHB Engine includes the following modules:
•
DMA
: Includes logic for the AHB master interface and contains the DMA controller.
•
Slave
: Includes logic for the AHB slave interface.
•
Decoder
: Address bus decoder module to divide accesses between MAC core, FIFO and accesses
to the registers within AHB engine.
The AHB engine includes a DMA controller which is used to transmit and receive operations. Both
operations compete for the use of the DMA controller. A round-robin priority algorithm is used to arbitrate
between the competing requests.
The AHB engine module interfaces with the host system through a 32-bit AHB master and slave ports.
The AHB engine module is positioned between the AHB system bus and the FIFO. Registers within the
AHB engine provide control and status information concerning these transfers.
11.2.1.2 MAC TX and RX FIFO
The A-MCXFIFO is a flexible FIFO module with the transmit buffering and the receive buffering, which
can significantly improve the performance of the embedded 10/100/1000 Mbps Ethernet systems. This
FIFO module offers increased system level throughput by allowing data queueing. The size of the
transmit buffer is 4 KB and the receive buffer is 8 KB.
Both automatic pause frame handshaking and per transmit frame MAC configuration data are supported.
A PAUSE frame is used for flow control. This halts the transmission for a specified period of time. A
PAUSE frame includes the period of pause time being requested.
Register definitions for the FIFO RAM access registers are intended for non-real-time RAM testing and
system debug. MAC TX and RX FIFO configuration registers one through five are intended to be written
while the submodules are held in reset. FIFO sizes are fixed and cannot be modified by either the MAC
configuration or the firmware.
11.2.1.3 PE-MCXMAC
The PE-MCXMAC provides a 10/100/1000 Mbps EMAC with a GMII interface. The PE-MCXMAC
supports control frames, particularly PAUSE frames. Other types of control frames can be supported
through the setting optional configuration bits.
The PE-MCXMAC module consists of the following six sub-modules.
11.2.1.3.1 PETFN Transmit Function
The PETFN sub-module accepts the transmit frames, and prepends a 7-byte preamble and start of frame
delimiter. The PETFN waits for the pre-programmed inter-packet gap before outputting the preamble.
11.2.1.3.2 PETMC Transmit MAC Control
The PETMC sub-module is responsible for the multiplexing of normal transmit frames and control frame
requests. It provides native support to the PAUSE flow control frames.
11.2.1.3.3 PERFN Receive Function
The PERFN sub-module accepts receive packets through the GMII, extracts frames, strips off the
preamble, and starts the frame delimiter from each frame before presenting them to the system. It also
calculates the cyclic redundancy check
(
CRC) of the received frame for checking against the Frame
Check Sequence field.
11.2.1.3.4 PERMC Receive MAC Control
The PERMC sub-module is responsible for detecting the control frames in the receive data stream. Each
frame is examined to determine if it is a control frame and if so, whether it is a PAUSE frame.
11.2.1.3.5 PEHST Host Interface
This 32-bit
interface gives access to the status and control registers included in the PE-MCXMAC.
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