Enabling Trusted Automotive Vision Using MIPI Interfaces & Protocols

Image sensors play a crucial role in advanced driver assistance systems and autonomous driving. Today, the systems used to deliver the most advanced SAE level-2 features typically utilize up to six cameras. This number is projected to increase significantly over time, potentially requiring up to 45 image sensors, including radars and lidars, to deliver the most advanced level-3 ADAS features and pave the way for higher levels of automation.

As the number of image sensors enabling these safety-critical systems has increased, MIPI Camera Serial Interface 2 (MIPI CSI-2), a standardized image sensor protocol developed by MIPI Alliance, has become the de facto imaging protocol used within these systems. 

Building upon the adoption of the CSI-2 protocol within automotive vision systems, MIPI Alliance has recently undertaken several automotive initiatives to support and streamline the use of the CSI-2 protocol in trusted, next-generation, safety-critical automotive vision systems. These initiatives address the automotive industry’s requirements for:

MIPI’s automotive initiatives have led to the creation of a MIPI automotive image sensor “stack” (see figure), an end-to-end framework for connecting image sensors using MIPI CSI-2, MIPI A-PHY and other standard protocols, with functional safety, security and resilience built in.

Figure: MIPI automotive image sensor “stack,” showing CSI-2 with security and functional safety.

Features for Automotive Vision Systems

The MIPI CSI-2 protocol is used to connect cameras and other high-speed sensors to application processors or image signal processors. The use of CSI-2 within automotive applications is augmented with MIPI Camera Service Extensions (MIPI CSE), which provides safety and security; and MIPI Camera Command Set (MIPI CCS), which provides command and control. CSI-2 supports several short- and long-reach physical layer (PHY) options, including A-PHY, which supports bridged and natively integrated options.

CSI-2 includes numerous features designed into the protocol that benefit automotive imaging systems. The features enable sensor aggregation optimization, superior objective image quality, and energy consumption reduction. Provisions within CSI-2 also alleviate RF emissions, support "region of interest" extraction, always-on inferencing, wire reduction, longer reach connectivity, and reduction of current leakage.

Features supported by CSI-2 that offer specific benefits to vehicle systems that make use of machine awareness, include:

The use of MIPI CSE enables an automotive system to fulfill ADAS safety goals up to ASIL D level (per ISO 26262:2018) and supports functional safety and security mechanisms including end-to-end protection as recommended for “high” diagnostic coverage of the data communication bus.

Industry-Standard Automotive SerDes Interface

To complement the use of CSI-2, MIPI Alliance developed A-PHY, a physical layer interface to address the need for a standardized long-reach, highly reliable, asymmetric SerDes solution to simplify the integration of image sensors into automotive. It is designed to meet the specific needs of the automotive industry, offering unprecedented resiliency and reliability, and eliminating the need for proprietary PHYs and bridges to connect cameras and displays in vehicles. The use of A-PHY simplifies in-vehicle communication networks, reducing cost, weight and development time.

Key features of A-PHY are:

The A-PHY physical layer can accommodate multiple higher-layer protocols through its generic data link layer and a set of protocol adaptation layers (PALs) that map these protocols to A-PHY’s A-Packet format. In addition to PALs that support native coupling to MIPI CSI-2, additional PALs have been developed for several lower-bandwidth control interfaces including I2C, GPIO, Ethernet, SPI and the emerging MIPI I3C interface.

A reference compliance test suite and compliance program under development will support A-PHY. A-PHY v1.0 has also been adopted as IEEE standard 2977™-2021.

End-to-End Application Layer Security

Safety-critical automotive vision use cases demand end-to-end data protection from data source, in an image sensor, to data sink, in an ECU. To address this need and further complement CSI-2, MIPI created a security framework that leverages authentication to protect against unauthorized system components, integrity protection to prevent manipulation of data, and confidentiality to protect data privacy.

The security framework has been designed to balance security requirements against the practical need to develop system components within tight power, size and heat tolerances. A key attribute to achieve this flexibility is the framework’s ability to support source-selective security, which enables a developer to "flex" the level of security to the structure of the upper layer application protocol. The security framework is also designed to maintain end-to-end security over a wide range of network topologies (e.g., for networks that leverage bridges, aggregators, etc.).

The initial security framework is defined within the following suite of security-related specifications:

When both security and functional safety service extensions are enabled, security is layered on top of functional safety—from a source (or transmitter) perspective, security is applied to the image data first, followed by the application of functional safety.

To learn more about the automotive initiatives that support and streamline the use of MIPI CSI-2 protocol for safety-critical and trusted automotive vision systems, MIPI experts will provide an extended tutorial at Drive World 2024. The tutorial will be relevant to automotive developers, system architects and engineering managers who are focused on the development, integration and test of next-generation automotive vision systems. MIPI experts supporting the tutorial include: Haran Thanigasalam, camera and imaging consultant at MIPI Alliance; Edo Cohen, co-chair of the MIPI A-PHY Working Group; and Rick Wietfeldt, co-chair of the MIPI Security Working Group.

The tutorial will take place Tuesday, January 30, from 9:00 to 11:30 a.m., at the Drive World at DesignCon Conference in Santa Clara, Calif.