MIPI Alliance rises to data-transport challenge
A revolution in automotive technology is making driving both safer and easier—and soon, fully automated. More and better cameras and displays, plus radar and LiDAR sensors, are helping to make this possible. The age of the hyper-aware vehicle is just beginning.
More data about a car’s surroundings improves driver assistance and is essential for self-driving systems. But sensors and screens are useless without fast, efficient connections to onboard computers. And this presents a central challenge: Despite these burgeoning needs, most vehicle networks were designed for a time before lane-keeping systems, multiple dash displays, and robo-taxis. As a result, automakers are now on a search for new interfaces that offer high performance, low cost, and less complexity.
MIPI A-PHY, a forthcoming automotive physical layer specification from MIPI Alliance, builds on years of innovation and real-world experience in mobile, IoT, and automotive interconnects to offer a new high-speed connectivity solution that is scalable, interoperable, and nonproprietary to meet a broad spectrum of design needs. The specification can increase performance, improve system integration and performance, and cut costs while coexisting with Ethernet and other protocols where needed.
Meeting new challenges
Automotive image sensors and displays have come a long way from the first rearview cameras and small dashboard screens. New car models have more cameras powering features such as lane-departure warning, road-sign detection, and mirror replacements—as well as multiple high-resolution displays.
Integration and connectivity are now major considerations in design and manufacturing. Goals for in-vehicle connectivity include saving space and weight, cutting costs, reducing complexity, and quickly bringing new features to market.
Today, most designs rely on proprietary SerDes (serializer/deserializer) chipsets for long-reach interconnects between sensors and processors as well as displays and processors. These lack standards-based economies of scale.
A-PHY, with an advanced draft already available to MIPI Contributor members, is a robust long-reach physical-layer specification initially aimed at automotive imaging and display systems. It will reach up to 15 m (49 ft) and support five speeds ranging from 2-16 Gbps in version 1.0, with a roadmap to 24 Gbps and greater. In addition, A-PHY allows all data to be transported over a single cable. These unique capabilities will make A-PHY an ideal long-reach interface for automated and autonomous cars.
Most automotive cameras and displays use the same MIPI specifications found in mobile devices: MIPI Camera Serial Interface-2 (MIPI CSI-2) and Display Serial Interface (MIPI DSI and DSI-2), layered on top of the MIPI C-PHY and MIPI D-PHY physical layer specifications. These are not long-reach specifications, so integrators have added proprietary SerDes bridge chips between C-PHY/D-PHY and long-reach interfaces.
A-PHY is expected to transform automotive interconnects in two phases.
In the short term, carmakers and system integrators can focus on the single long-reach PHY standard, A-PHY, to reduce complexity and cost in the ecosystem (see Figure 2).
As more components support A-PHY, OEMs and integrators will be able to implement native CSI-2 and DSI-2 interfaces without C-PHY and D-PHY. Cameras and displays will be able to use CSI-2 and DSI-2 natively over A-PHY. This elegant end-to-end architecture, unique to A-PHY, will reduce cost, complexity, wiring, weight, and use of space.
A-PHY coexists with Ethernet and other automotive interfaces such as CAN, FlexRay, LIN, and others. While multi-gig Ethernet is used to connect domain or zone ECUs as the backbone in the in-vehicle connectivity network, A-PHY’s focus is on display and high-bandwidth sensor connectivity to the domain or zone ECU (see Figures 3 and 4).
Here are a few of the ways automotive OEMs and integrators will be able to deploy MIPI A-PHY (as illustrated in Figure 5):
- Camera/radar/LiDAR to domain ECU: A-PHY can be the physical interface between an imaging domain ECU and one or more cameras or other sensors.
- Infotainment to display modules: A-PHY will carry display data and user experience control commands between a touchscreen and an onboard computer anywhere in the vehicle. The DSI-2 interface protocol for video data and display control, as well as MIPI I3C for touch commands, can be transported natively over A-PHY.
- Daisy chaining of devices: Sensors can be daisy chained, with one or more cameras in the same part of the vehicle, and with all the data streams backhauled over the same A-PHY transport to a domain or central ECU. Similarly, multiple display streams can be transported from an infotainment ECU to multiple displays connected in a daisy chain. This reduces complexity, wiring, weight, and costs.
A-PHY also offers other features and benefits specifically designed for automotive:
- Asymmetric architecture: A-PHY provides high-speed, unidirectional data, bidirectional control data, and optional power delivery on a single cable. This results in less complexity and lower cost and weight relative to symmetric alternatives, such as Ethernet.
- Hardware-only protocol layers: Tightly coupled with CSI-2/DSI-2, A-PHY essentially operates without software intervention, reducing complexity.
- Generic data link layer: The A-PHY data link layer will support approved third-party protocol adaptation layers, so developers will be able to reuse other standards.
- High EMC immunity: Designed specifically for harsh automotive environments, A-PHY features close-loop control with Narrowband Interference Cancellation (NBIC) and PHY-level Retransmission Scheme (RTS). These features protect high-data-rate transmissions from electromagnetic interference resulting in superior EMC immunity.
- Daisy chaining and stream duplication: A-PHY supports daisy chaining to connect multiple cameras or displays to an ECU on a single link, reducing the cable harness. It also features streams duplication, which enables safety through redundancy.
- Functional safety: A-PHY, along with the native protocols and their respective adaptation layers, features end-to-end functional safety according to ISO 26262 with support for up to ASIL-D.
- Security: Imaging security and content protection are supported as needed by the tightly coupled native protocols and their respective adaptation layers.
Freedom of choice
Automakers and system integrators can optimize A-PHY for the performance, cost, and complexity required by their use cases.
MIPI A-PHY v1.0 supports simple lowest-cost implementations using NRZ-8b10b encoding in its lower two speeds 1 and 2 supporting 2 and 4 Gbps, respectively, and 8 Gbps when implemented jointly with the high-performance features NBIC and RTS in speed 3. These high-performance features support all A-PHY speeds up to 5 at 16 Gbps for v1.0 and has a scalable architecture to address higher speeds going forward.
The NBIC and PHY-level retransmission ensure maximum reliability/robustness of the A-PHY link.
A major step in automotive connectivity
Standard interfaces in mobile devices have helped the mobile industry continually improve performance and features while driving down cost and power consumption. This potential is now coming to automotive in the form of MIPI A-PHY, which is poised to play the same role in cars as MIPI C-PHY and D-PHY play in smartphones, IoT devices, and tablets.
The introduction of A-PHY builds on the long history of successful MIPI specifications adopted by the mobile industry and updated for its evolving needs. Automotive now has its own standard, long-reach interface, optimized for demanding environments, and a clear roadmap aimed at future self-driving and highly automated vehicles.
All MIPI specifications are royalty free for MIPI members. To learn more about MIPI in automotive, download the “Driving the Wires of Automotive” white paper (https://bit.ly/395pDqU).