GR740-UM-DS, Nov 2017, Version 1.7
204
www.cobham.com/gaisler
GR740
14
Gigabit Ethernet Media Access Controller (MAC)
14.1
Overview
Cobham Gaisler’s Gigabit Ethernet Media Access Controller (GRETH_GBIT) provides an interface
between an AMBA-AHB bus and an Ethernet network. It supports 10/100/1000 Mbit speed in both
full- and half-duplex. The AMBA interface consists of an APB interface for configuration and control
and an AHB master interface which handles the dataflow. The dataflow is handled through DMA
channels. There is one DMA engine for the transmitter and one for the receiver. Both share the same
AHB master interface.
The ethernet interface supports the MII and GMII interfaces which should be connected to an external
PHY. The GRETH also provides access to the MII Management interface which is used to configure
the PHY. Hardware support for the Ethernet Debug Communication Link (EDCL) protocol is also
provided. This is an UDP/IP based protocol used for remote debugging.
Some of the supported features for the DMA channels are Scatter Gather I/O and TCP/UDP over IPv4
checksum offloading for both receiver and transmitter.
The system contains two GRETH_GBIT cores. The AHB master interfaces are connected to the Mas-
ter I/O AHB bus. The cores also gave dedicated EDCL interfaces connected to the Debug AHB bus.
The selection of which master interface to use for EDCL traffic is made via bootstrap signals.
14.2
Operation
14.2.1 System overview
The GRETH_GBIT consists of 3 functional units: The DMA channels, MDIO interface and the
optional Ethernet Debug Communication Link (EDCL).
The main functionality consists of the DMA channels which are used for transferring data between an
AHB bus and an Ethernet network. There is one transmitter DMA channel and one Receiver DMA
channel. The operation of the DMA channels is controlled through registers accessible through the
APB interface.
Figure 16.
Block diagram of the internal structure of the GRETH_GBIT
AHB
APB
Ethernet MAC
Registers
MDIO
ETH*_MDIO
ETH*_MDC
AHB Master
Interface
Transmitter
Receiver
Transmitter
Receiver
DMA Engine
DMA Engine
RAM
RAM
ETH*_TXEN
ETH*_TXER
ETH*_TXD[7:0]
ETH*_TXCLK
ETH*_CRS
ETH*_COL
ETH*_RXDV
ETH*_RXER
ETH*_RXD[7:0]
ETH*_RXCLK
EDCL
Transmitter
EDCL
Receiver
ETH*_GTXCLK