Ethernet Connectivity via GPMC

Purpose

The purpose of this article is to describe a solution for connecting Ethernet to various devices, such as OMAP35x and AM37x, via GPMC.

Block Diagram

Schematics

Below is one example of connecting an Ethernet MAC/PHY using the SMSC LAN9220. Vist the OMAP3530 download page on Mistral's site to get the complete schematic solution.

Performance Measurements

These numbers are taken from the PSP Feature Performance Guide

Ethernet TCP - 100Mbps Mode Performance

TCP Window Size (in KBytes)	Bandwidth - OMAP35x (in Mbits/sec)	Bandwidth - AM3517 (in Mbits/sec)	Bandwidth - AM/DM37x (in Mbits/sec)
16	47.2	22.2	54.9
32	47.3	38.4	56.1
64	46.6	64.6	53.8
128	46.5	87.1	53.8

The performance numbers were captured using the iperf tool. Usage details are mentioned below:

• On the DUT iperf is invoked in client mode  : "-c <server ip> -w <window size> -d -t60"
• On PC Host invoke iperf in the server mode  : "-s" - window size default of 212KB
• The transfers are measured over a duration of 60Secs
• Cross cable is used to measure performance.
• Speed is set to 100Mbps
• Power Management disabled for measurement

Ethernet UDP - 100Mbps Mode Performance

UDP Buffer Size (in KBytes)	Bandwidth - OMAP35x (in Mbits/sec)	Bandwidth - AM3517 (in Mbits/sec)	Bandwidth - AM/DM37x (in Mbits/sec)
16	60.6	101	48.6
32	60.6	100.9	48.8
64	60.7	100.9	48.9
128	60.6	110.1	48.7

The performance numbers were captured using the iperf tool. Usage details are mentioned below:

• On the PC Host iperf is invoked in client mode  : "-c <server ip> -w <window size> -d -b 100M -t60"
• On DUT invoke iperf in the server mode  : "-s -u -w 256k "
• The transfers are measured over a duration of 60Secs
• Cross cable is used to measure performance.
• Speed is set to 100Mbps
• Power Management disabled for measurement

Software

Drivers can be found as part of the u-boot source code found in the PSP (OMAP35x PSP). Relevant functions are likely to be found in the following directories:

• u-boot_src\net\
• u-boot_src\drivers\net

For an example on using some of this code, refer to the ITBOK source. Specifically, the ethernet_test() function found in ITBOK_src\EVM3530_ITBOK\diagnostics\src\automation.c. Here is a sample output of what the function performs:

Starting Ethernet Test...
Server IP address is 192.168.1.1
smc911x: detected LAN9220 controller
smc911x: phy initialized
smc911x: MAC 00:50:c2:7e:8e:58
Using smc911x-0 device
host is alive

Ethernet Test Completed... PASS

FAQs

Are gigabit Ethernet speeds possible?

Currently, there are no reference designs available for gigabit Ethernet. However, Asix provides the AX88180, a gigabit Ethernet controller.

What other Ethernet PHYs can I use?

The LAN9115, LAN9220 and LAN9221 from SMSC have been implemented with the OMAP35x processor.

Is it possible to get better performance than what is stated in the PSP documentation?

Some users have seen better performance using the LAN9221. See this forum thread for more details.

Useful Links

Ethernet Driver Details - Contains information about the Linux driver, including performance measurments for OMAP35x, AM35x and AM/DM37x devices.

AM/DM37x Overview

ARM and DSP Microprocessors Forum

Demystifying Ethernet Performance