Gbit Ethernet

Receive and transmit data is autonomously transferred between the Ethernet MAC and the AMBA AHB bus using DMA transfers. Through the use of receive and transmit descriptors, multiple ethernet packets can be received and transmitted without CPU involvement. The GRETH_GBIT provides support for the MII and GMII PHY interfaces. Hardware support is also provided for the EDCL UDP debugging protocol. For critical space applications, a fault-tolerant version of GRETH_GBIT is available with full SEU protection of all RAM blocks.

EDCL

The EDCL is an optional hardware unit providing read/write access to the AHB bus through Ethernet using an UDP based protocol. It operates in parallel with the MAC DMA and does not interfere with the  normal network traffic other than lowering performance. Speeds up to 500 Mbit/s effective throughput have been achieved when accessing the AHB bus through the EDCL using the GRMON debug monitor.

The IP can be implemented in any ASIC or FPGA technology. For specific information related to Xilinx, Microchip, and Lattice FPGAs, please refer to our dedicated web pages:

• Specific support for Lattice FPGAs
• Specific support for Microchip FPGAs
• Specific support for Xilinx FPGAs

Estimation of the resource utilization can be found here: Excel sheet for SoC area estimation

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The GRETH_GBIT core can be licensed commercially, either stand-alone or as part of the GRLIB IP library. Contact sales@gaisler.com for licensing information

Speed with TCP/IP software stacks

Although the theoretical maximum speed is near 1 Gbit/s for a gigabit network this is never reached in practice. When using software TCP/IP stacks from the supported operating systems the limiting factor will be the processing power of the CPU. The tables below show the speed that can typically be achieved with different CPU configurations using Linux 2.6 which has the most extensive support for the offloading features in the GRETH_GBIT. The other operating systems will usually be slower since they lack support for one or more of these features. The speed measurements were done with the Test TCP (TTCP) utility which is a benchmarking tool for measuring TCP and UDP performance. The Tx and Rx columns in the tables refer to the speed achieved when transmitting and receiving with TTCP respectively. All the tests were run in TCP mode.

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