The modern automobile is loaded with electronics. Simple electronics of the mid- to late-20th century like electronic ignition and 8-track/cassette audio has been replaced with controls on everything. Examples include ABS, suspension/stability control, fuel injection, engine pollution controls, and advanced driver-assistance systems (ADAS), as well as satellite radio, GPS navigation, Wi-Fi hot spots, Bluetooth hands-free controls, and streaming audio.
In turn, all of this has given rise to the need for wired networks to organize the various subsystems and cut down on the amount of wiring needed. Simple networks like the local interconnect network (LIN) and controller area network (CAN) have been used for years.
But, as cars became more connected, faster networks like FlexRay and Media Oriented Systems Transport (MOST) were adopted. Now, though, newer vehicles are required to handle even greater amounts of data at ever-higher speeds, which has led to the adoption of Ethernet. In addition, gateways that consolidate those slower networks also evolved to meet this need.
- Automotive Stand-Alone Gateway Reference Design with Ethernet and CAN
- Automotive gateways: the bridge between communication domains
- The rise of automotive Ethernet
Ethernet first emerged from the Xerox Palo Alto Research Center in 1973 as a coax-based bus design. It was then standardized by the Institute of Electrical and Electronics Engineers (IEEE) as 802.3. Then over the years, it was updated and enhanced to produce many different versions. The coax standards were replaced by twisted-pair and fiber versions. And higher-speed variations arrived. The initial 10-Mb/s speed has seen gradual upgrades to 100 Mb/s, 1 Gb/s, 10 Gb/s, and 100 Gb/s.
The 1- and 10-Gb/s twisted-pair versions are the most popular today, as are related standards such as Power over Ethernet (PoE) that furnishes dc power to remote nodes. Older, slower versions are also still popular in many applications.
Ethernet was and still is primarily used for commercial office local-area networks. However, a hardened version known as Industrial Ethernet has emerged to serve industrial automation applications. It has steadily replaced legacy data-communications connections like RS-232, RS-485, and a variety of fieldbuses (Modbus, Profibus, etc.) that have developed over the years.
In 2016, the IEEE introduced another version designated 802.3bw for automotive applications. Also called 100Base-T1, this standard supports 100-Mb/s data on a single, balanced twisted-pair cable. In addition to meeting the need for high speed, this new standard will help reduce and simplify the cumbersome, heavy, and complicated wiring harnesses used today.
In the physical layer (PHY) of the 100Base-T1 standard, data is transmitted over a single copper twisted pair. To achieve the 100-Mb/s data rate, it uses 3 bits per symbol (PAM3). The standard supports full-duplex operation, which means transmission in both directions simultaneously. The twisted-pair cable must support a minimum of 66 MHz, with a maximum length of 15 m. No specific connector is defined.
Some vehicles also incorporate another version of Ethernet designated as 802.3u or 100Base-TX. It supports 10- or 100-Mb/s data rates, but uses a cable with two twisted pairs. This version of Ethernet is sometimes used for diagnostics by way of the onboard diagnostic port (OBD II).
Traditional automotive networks will continue be used to interconnect the various electronic control units (ECUs) throughout the vehicle. There are ECUs for the engine, body, power train, infotainment, and the OBD II. These subsystems talk to one another by way of a gateway. The gateway provides communications via an Ethernet port.
A gateway serves as a bridge between ECUs and provides a way to translate from one protocol to another so that the different subsystems can exchange data. Gateways manage the whole communications process. The figure shows an automotive gateway. The various subsystems or connected domains within a vehicle connect by CAN, LIN, FlexRay, or MOST networks. For example, powertrain domains may use CAN or FlexRay. Body domains typically employ LIN and/or CAN. Infotainment domains may use MOST.
As shown in this general block diagram of an automotive system, a gateway employs a main Ethernet switch and transceiver. The gateway consolidates multiple automotive interfaces and provides protocol conversions and general data-flow management. (Courtesy of Texas Instruments)
At the heart of the gateway is a central MCU or processor to handle the protocol conversions and other functions. In some systems, auxiliary MCUs may be needed to manage the data. Note that the main MCU or processor has a built-in Ethernet switch that then connects to the vehicle’s main Ethernet bus.
With more electronics being packed into cars, it’s significantly increased the data load, especially with the addition of Ethernet. This has led to new gateways that replace the smaller MCUs with a larger, faster processor. Such processors have separate external memory and higher processing power. A larger processor can also run an operating system such as Linux to manage the complex processing.
Designing an automotive Ethernet gateway is a challenge for any engineer. One good starting point is to use Texas Instruments’ TIDA-01425, a subsystem reference design for automotive gateways. Its prime focus is on increasing bandwidth and processing power in gateways for the coming electronics-laden vehicles. The design combines Ethernet physical-layer transceivers (PHYs) along with an automotive processor for greater processing capabilities, allowing automotive gateways to pass more data at higher speeds.
Some of the key features of the reference design are:
- Powerful DRA710 J6Entry processor with external DDR3 RAM.
- Internal Gigabit Ethernet switch
- 3bw 100Base-T1 Ethernet PHY
- 3u 100Base-TX Ethernet PHY
- Two CAN PHYs
- Required dc-dc converters and regulators
The DRA710 processor is based on the ARM Cortex-A15. Also on-chip is a TI C66x DSP co-processor and a GPU. There’s 512 kB of L3 RAM on-chip, too, as well as a memory controller for 2 GB of external RAM. Interfaces include multiple USB, UART, SPI and I2C ports.
The Ethernet ports are implemented with TI’s PHY transceivers. The DP83848Q-Q1 covers the 100Base-TX port and two TCAN1042-Q1 transceiver chips implement the CAN ports. Note that a key feature of all these devices is that they operate over the wide temperature range of −40°C to 125°C, making them ideal for the harsh automotive environment.