Octavo OSD335 AM335 Series Guida

Using Ethernet with OSD335x-

AM335x System in Package

Rev.1 5/23/2019

Octavo Systems LLC

1Introduction

The Texas Instruments AM335x processor used in the OSD335x Family of System in

Package Devices supports up to two independent Gigabit Ethernet ports (10/100/1000

Mbps). This application note will help you quickly get started interfacing an Ethernet

PHY with the OSD335x, the AM335x System in Package, Family of Devices. This

document will showcase reference designs, which can be used as design examples,

make recommendations on layout, device trees and provide tips on debugging AM335x

Ethernet issues.

Notice: The information provided within this document is for informational use only.

Octavo Systems provides no guarantees or warranty to the information contained.

Using Ethernet with OSD335x-

AM335x System in Package

Rev.1 2/18/2019

Octavo Systems LLC

Table of Contents

1Introduction ....................................................................................0

2Choosing the Right Ethernet PHY............................................................2

2.1 Reference Designs Using AM335x Ethernet............................................2

2.2 Additional Ethernet PHYs ................................................................3

3Design Example and Recommendations for Using Ethernet with the AM335x System

in Package ..........................................................................................4

3.1 Schematics.................................................................................4

3.2 Layout ......................................................................................7

3.2.1 Dual Ethernet Example ..............................................................9

4Setting up Ethernet (Device Tree) ........................................................ 11

5Debugging Tips ............................................................................... 15

5.1 Software Issues.......................................................................... 15

5.2 MAC to PHY Connections............................................................... 15

5.3 PHY to RJ45 Port Connections ........................................................ 15

5.4 Data Errors............................................................................... 16

6Revision History .............................................................................. 16

2 
Using Ethernet with OSD335x- 
AM335x System in Package 
Rev.1 2/18/2019 
Octavo Systems LLC 
Copyright 2019 
2Choosing the Right Ethernet PHY 
The AM335x processor within the OSD335x, the AM335x System in Package, Family of 
Devices contains two Ethernet MAC (Medium Access Control) peripherals that can be 
used independently or together with an integrated switch. Each MAC supports MII, 
RMII, RGMII and MDIO interfaces that can be used to connect to an Ethernet PHY 
(Physical Layer), which in turn is connected to an Ethernet port. This allows Ethernet 
cables to connect the AM335x to the rest of the network. 
 
Ethernet PHYs are available from many different manufacturers and have a wide range 
of features. The most significant features to consider when choosing an Ethernet PHY 
are: 
 1. Power Consumption 
2. Throughput/Speed –10/100/1000Mbps 
3. Package type and size 
4. Driver support 
5. Hardware Errata 
6. Ease of availability 
 
2.1 Reference Designs Using AM335x Ethernet 
Reference Designs using the AM335x Ethernet with different PHYs are listed below so 
that you can choose the best fit for your requirements and jump-start your design. 
 1. AR8035 based OSD3358-SM-RED design from Octavo Systems –
https://octavosystems.com/files/osd3358-sm-red-eagle-files/ 
 
2. AR8035 based C-SiP RED design from Octavo Systems –
https://octavosystems.com/files/osd3358-sm-red-c-sip-eagle-files/ 
 
3. LAN8710 based SBC Reference design from Octavo Systems –
https://octavosystems.com/files/osd3358-bas-sbc-reference-design-files/ 
 
4. AR8031 based Dual Ethernet design from TI Starter Kit –
http://processors.wiki.ti.com/index.php/AM335x_StarterKit_Board_Design_Files 
 
5. KSZ9031 based Dual Ethernet design shown in Figure 1, Figure 2, Figure 4 and 
Figure 5 –design files will be published soon. 
 

Using Ethernet with OSD335x-

AM335x System in Package

Rev.1 2/18/2019

Octavo Systems LLC

2.2 Additional Ethernet PHYs

Below is a list of additional Ethernet PHYs from major manufacturers. This is not a

comprehensive list but can be used in case there are issues with availability of the

PHYs in the reference designs listed above.

•Texas Instruments:

http://www.ti.com/interface/ethernet/phy/overview.html

•Microchip:

https://www.microchip.com/design-centers/ethernet/ethernet-

devices/products/ethernet-phys

•Marvell:

https://www.marvell.com/transceivers/fast-ethernet-phy/

•Broadcom:

https://www.broadcom.com/products/ethernet-connectivity/

•Microsemi:

https://www.microsemi.com/product-directory/ethernet-solutions/3581-physical-

layer

For any PHY selection, we strongly recommend that you can purchase the part through

a major distributor, such as DigiKey or Mouser, and that the part has plenty of stock

available.

Using Ethernet with OSD335x-

AM335x System in Package

Rev.1 2/18/2019

Octavo Systems LLC

3Design Example and Recommendations for Using Ethernet

with the AM335x System in Package

The following figures show an example of a dual AM335x Ethernet design using the

KSZ9031 Ethernet PHY to communicate with the Ethernet MAC peripherals on the

OSD335x, the AM335x System in Package, Family of Devices. The figures walk

through the schematics and layout. Reference design files for this design will be

available in the future. Please sign up for documentation updates to be notified when

they are available.

3.1 Schematics

When connecting an Ethernet PHY, you need to be aware of the default PHY

configuration pull-up / pull-down resistors. Most PHYs utilize a number of pins to set the

initial configuration of the device, such as the PHY address on the MDIO bus. It is

important that all of these configuration pins are set correctly. For example, in the figure

below, you can see the pull-up / pull-down resistors on the RX and LED interfaces that

will set the initial configuration of the PHY.

Using Ethernet with OSD335x-

AM335x System in Package

Rev.1 2/18/2019

Octavo Systems LLC

Figure 1 - PHY 1 Ethernet Connections

Using Ethernet with OSD335x-

AM335x System in Package

Rev.1 2/18/2019

Octavo Systems LLC

Figure 2 - PHY 2 Ethernet Connections

When creating a dual AM335x Ethernet design, it is critical that each PHY have a

different MDIO address. This will allow the single MDIO bus to communicate and

configure each PHY. Additionally, it is important to know the MDIO address of

the PHY since that will be necessary when we set up the device tree for the

Ethernet PHY.

Using Ethernet with OSD335x-

AM335x System in Package

Rev.1 2/18/2019

Octavo Systems LLC

3.2 Layout

When laying out an Ethernet PHY, there are two different sets of connections: MAC to

PHY and PHY to RJ45 connector (i.e. the Ethernet port). The MAC to PHY connections

for the OSD335x Family of devices uses MII, RMII or RGMII. These have a bus speed

of 25 MHz, 50 MHz, 125 MHz, respectively. The PHY to RJ45 connections use

differential Ethernet signaling in the 10s to 100s of MHz depending on the Ethernet

speed required for the link.

The following are some general recommendations for Ethernet PHY layout design:

1. Use only 45o/135oangles in traces to avoid signal reflections.

2. Trace widths should be constant to maintain uniform impedance.

3. Length match TX_CLK, TXDx and RX_CLK, RXDx signals between AM335x and

Ethernet PHY. Depending on the interface type, the tolerance for length

matching becomes tighter due to the higher bus speeds

4. Length match TX+,TX- and RX+, RX- traces between Ethernet PHY and RJ45

connector/magnetics module. We have found that RJ45 connectors with an

integrated magnetic module are easier to route.

5. Keep the overall trace length between AM335x and RJ45 connector < 75mm.

6. If the RJ45 connector (with thru-hole pins) is placed on the top layer, route traces

to its pins on the bottom layer to avoid signal stubs caused by the thru-hole pins.

7. Avoid vias and layer changes for Ethernet traces.

Using Ethernet with OSD335x-

AM335x System in Package

Rev.1 2/18/2019

Octavo Systems LLC

Figure 3 - OSD3358-SM-RED Ethernet PHY Layout Example

Using Ethernet with OSD335x-

AM335x System in Package

Rev.1 2/18/2019

Octavo Systems LLC

3.2.1 Dual Ethernet Example

When laying out a dual AM335x Ethernet design, we recommend that you focus on

careful placement and routing of a single Ethernet PHY and port. Once that Ethernet

PHY and port are placed and routed to your satisfaction, the layout can be replicated

easily for the second Ethernet port. You can see an example of this in the figures below

when looking at both the signal routing and power layout.

Figure 4 - Dual Ethernet Top and Bottom Layer Example

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