Cadence gears up for automotive switch to ethernet

Cadence Design Systems has developed semiconductor IP for an initiative driven by the automotive industry to make ethernet the core networking backbone of future motor vehicles.

Ethernet is already used for onboard diagnostics and firmware downloads because it offers much higher bandwidth than the Controller Area Network (CAN). Figures put together by Thomas Thomsen and Georg Drenkhahn from EB Automotive in 2008 for the First Autosar Open Conference showed that it could take ten hours to flash the 81Mbyte of firmware inside a fourth-generation BMW 7-series vehicle using CAN. A fifth-generation 7-series bumped up the firmware to 1Gbyte but this could be flashed in just 20 minutes using Ethernet.

Now, ethernet is reaching out into other subsystems within the car but, as they have real-time and more stringent electrical performance needs, the ethernet interface itself is changing to accommodate them. Cadence has designed its IP, and supporting verification IP, around the standards package being thrashed out by the One-Pair Ethernet (OPEN) Alliance, which numbers carmakers such as BMW, GM and Volkswagen among its members. Also involved are chipmakers such as NXP Semiconductors and Broadcom, which is licensing its BroadR Reach technology to companies that adopt the OPEN Alliance scheme to reduce electromagnetic interference (EMI) from the lightweight unshielded twisted-pair cabling that carmakers want to use.

“The third most expensive part of a car after engine and body is the cable harness,” says Robert Schweiger, director of technology solutions for automotive at Cadence EMEA. “There is a lot of potential to save cost using unshielded twisted pair cabling rather than shielded twisted-pair. But as it also saves weight, it can help reduce gasoline consumption.”

The OPEN Alliance is not the only group working on automotive ethernet. The AVnu Alliance comes from an audio-video networking background and sees a future in automotive because of the growth in infotainment and camera-based systems in cars. AVnu members Micrel and Marvell have developed a relatively simple front-end filtering scheme for existing PHYs that the companies claim can bring emissions down to the required level and allow use with existing off-the-shelf ethernet devices.

However, the OPEN Alliance has both an eye on the core control network in a car as well as the audio and video subsystems, so is defining a modified media-access controller (MAC) that can deliver more deterministic performance. Schweiger says the plan is to work on an architecture that has a star-wired ethernet backbone with “virtual subnetworks that could use different bus protocols, such as CAN and LIN”.

“But ethernet from the computer world is only a best-effort network. Best effort is not acceptable for a car. You need reserved bandwidth for safety-critical applications. If you hit the brake you don’t want the vehicle to stop ten seconds later because of congestion on the network,” says Schweiger. “The key requirement that was defined by the OPEN Alliance was real-time support, providing features such as time-stamping in the MAC.”

Schweiger says existing IEEE standards such as 802.1as for time synchronization are being incorporated into the OPEN Alliance package of recommendations. Schweiger says there is an option to work also with the AVnu group to develop a combined set of requirements that will support other industries that want real-time guarantees for audio and video – in broadcast, for example – as well as automotive.

Cadence’s IP package is aimed at the semiconductor suppliers developing microcontrollers for ECUs and includes, as well as the core MAC design, a package of verification IP and transaction-level models to support virtual prototypes.

Schweiger argues: “Introduction of Ethernet will represent the biggest change to the electrical architecture of the car. It is not just about introducing a new network protocol. The main drivers are the bandwidth and cost reduction. But right after that we see a key driver being the flexibility of the network architecture that ethernet allows. It will allows the convergence of legacy protocols with new network technologies.”