Automotive industry players, including OEMs, Tier 1 suppliers, and semiconductor manufacturers, recently announced the launch of the OpenGMSL Association (OGA), driving an open standard for serializer/deserializer (SerDes) transmission of video and high-speed data for in-vehicle connectivity. The initiative is centered on Analog Devices Inc.’s (ADI’s) Gigabit Multimedia Serial Link (GMSL) SerDes technology that delivers high-speed video connectivity up to 12 Gbits/s.

GMSL, initially a proprietary technology, offers several benefits for high-speed video and sensor data transmission in advanced driver-assistance systems (ADAS), in-cabin infotainment, and autonomous driving. It offers a low bit-error rate, low latency, and low power, and it supports video splitting, daisychaining, and sensor data aggregation. In addition, it offers real-time link diagnostic capability, supports ASIL-B-rated devices, and meets stringent EMI/EMC requirements. It also offers backward compatibility to the previous generation.

GMSL is a “very road-proven, robust technology,” said Yasmine King, ADI’s corporate VP and head of the automotive business unit. By making GMSL an open standard with proven reliable and robust technology that anyone can design to, it will be the fastest way for the industry to move toward faster time to market, lower costs, and higher resiliency, she added.

“We are writing a channel specification that will encompass things like the physical layer, the data link layer, the protocol adapters, and the hardware register abstraction layer,” King said. “Basically, all of the information that a semiconductor design team would need to know to develop a solution that can plug right into a GMSL channel and interoperate.”

GMSL offers an open standard for connectivity of high-definition video and sensor (cameras, radar, and LiDAR) data in ADAS, in-cabin infotainment, and autonomous-driving systems. (Source: Analog Devices Inc.)

As demand increases for automotive systems such as ADAS, infotainment, and autonomous driving, so does the component count for vehicle cameras and displays that require real-time and high-resolution and high-speed video connectivity. ADAS vision systems, for example, require high-quality video data to make critical, real-time decisions that improve driver safety and reduce accidents, while touchscreen infotainment systems need high-speed, low-latency connectivity for immersive experiences.

“When you have to sense what’s happening in the environment around the vehicle, all that sensing puts more demand on the data rate that needs to be transmitted throughout the entire vehicle,” King said. “A lot of it tends to be video, so cameras are often used; radar and LiDAR are other pieces of sensing that get transmitted across GMSL, and this increases the number of sensor nodes in the vehicle.

“All of that sensing capability requires robust, very reliable data links inside the car, and so the network inside the vehicle is becoming extremely critical,” she added.

Why make GMSL an open standard?

GMSL started out as a proprietary standard in 2008 and is now on its third generation, with more than 1 billion chips shipped to 25 global OEMs and 50 Tier 1 suppliers.

There are three industry standards for automotive SerDes: MIPI A-PHY, ASA-ML, and High-Speed Media Transmission in China for high-speed in-vehicle data transmission.

According to King, these standards do not have proven silicon on the road. Aging is a concern, she said: “How do these technologies operate after seven or eight years of use on a daily basis? They haven’t proven themselves from a reliability and robustness standpoint.”

ADI’s GMSL technology aggregates and transmits data over long distances and can deliver high-speed video links over a single wire. With each new generation—GMSL1, GMSL2, and GMSL3—it has added new features that support higher resolution and deliver greater flexibility as the automotive industry shifts to a software-defined vehicle (SDV) architecture. New features such as daisychaining and higher data-rate capabilities have been added recently.

One of the biggest differences between the generations is the resolution supported. “Each of these generations has iterated to allow for higher resolution,” King said. The first cameras were 3 MP, jumping to 6 MP and then 8 MP, and it’s going even higher, she added.

“Vehicles are moving to higher-resolution cameras, like the forward-facing 8-MP camera becoming fairly common, or on the wing mirrors, you might be aggregating two or three cameras together,” she said. “All of that is driving up the bandwidth resolution required. You also have pillar-to-pillar displays inside the vehicle, and that is requiring higher data rates. So GMSL is a very good technology for supporting all of those capabilities.”

For ADAS applications, for example, GMSL supports forward cameras (8–15 MP), surround-view cameras (2–3 MP), driver-monitoring systems (2–5 MP), occupant monitoring (1–3 MP), pillar cameras (5–8 MP), side cameras (2–3 MP), eMirror cameras (5–8 MP), and LiDAR (3–5 Gbits/s).

Increasing demand for vehicle cameras, sensors, and displays that require real-time and high-resolution and high-speed video connectivity drives the need for an open video connectivity standard. (Source: Analog Devices Inc.)

ADI is in the process of doubling the 12-Gbits/s data-rate capability in the next generation, expected in 18 to 24 months. “We will work with the OpenGMSL Association to make sure that we are aligned now with partners, but in the meantime, we are working to get an initial definition written,” King said.

GMSL also offers backward compatibility to the previous generation, providing greater scalability for customers. “Customers can change one small link at a time and still know that they’re backward-compatible by a generation,” she said.

Flexibility is also important when routing multiple video cables throughout the vehicle. “We have an extremely low bit-error rate, which means that you can have longer cable lengths inside of the vehicle,” King said. “So as you’re building larger cars or just trying to eliminate cables or harnesses, you can now extend longer reaches inside the vehicle and still get very good-quality data without a lot of errors.”

The daisychain capabilities enable simultaneous display partitioning using a single cable. “Instead of routing multiple cables to displays, you may want to just route a singular cable and keep that cable connection going throughout the vehicle instead of having multiple connections back to the central compute,” she said. “The goal is to reduce the weight of the vehicle and increase the reliability so that you can get better fuel efficiency and better robustness in the long term.”

King said as the automotive industry moves from a more domain-based architecture to an SDV architecture, it requires a flexible technology that supports capabilities such as video splitting and daisychaining to meet the requirements of car manufacturers at various stages in the transition to a zonal architecture.

“When you’re making that transition, having interoperable open standards allows for faster time to market, lower cost, and higher resiliency, which is why we’ve been seeing this demand for an open standard when it comes to video connectivity solutions,” King said.

A key reason why open standards are important in the automotive industry is because automakers are shortening the development cycles of new or refreshed models at a much faster pace. Car model refreshes in China, for example, are at about 12 to 18 months, whereas it used to be about six years, and now the goal is to get to nine months, King said.

“Automakers need to move faster and faster with their car model refreshes, and that is very difficult to do when you have a bunch of different proprietary technologies and need to adapt across all these different model refreshes at a fast rate,” she explained. “This means a lot of OEMs are looking to create a unified or at least as much of a unified as possible platform that can scale from entry-level vehicles to premium-level vehicles with consistent hardware and then differentiate on the software piece of it.”

The industry is focused so much on video because of things like autonomous driving and ADAS, which are heavily reliant on video connections, she said. “We came to the realization that by opening GMSL, which had been a proprietary solution, and making this an open standard in the industry because it is a proven reliable, robust technology, it will be the fastest way for the industry to make this transition to an open standard.”

Products developed using the standard will require mandatory compliance testing to ensure seamless, multivendor interoperability. ADI is partnering with interoperability test houses, such as Granite River Labs, for example, to ensure solutions from different companies can work together. There are also several test providers that support OGA, including Keysight Technologies Inc., Rohde & Schwarz, and Teledyne LeCroy.

“It’s going to allow for interoperability and encourage product innovation across a wider set of silicon providers in the industry,” King said.

Other supporters range from system solution providers to semiconductor and passive component manufacturers. They include Aptiv PLC, Coilcraft Inc., Core Microelectronics, Denso Corp., Ethernovia Inc., Geely Holding Group, GlobalFoundries, indie Semiconductor, Hyundai Mobis, Murata Manufacturing Co. Ltd., Noffz Technologies, Omnivision, Qualcomm Technologies, Rosenberger Group, TDK Corporation, TZ Electronic Systems GmbH, and Würth Elektronik.

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