An overview of MIPI’s standardized in-vehicle connectivity framework for high-performance sensors and displays

MIPI White Paper: An Introductory Guide to MIPI Automotive SerDes Solutions (MASS)

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Contents

1. Executive Summary
2. Overview of Automotive Market Trends and Challenges
3. Introduction to MIPI Automotive SerDes Solutions (MASS)
4. The MASS Framework
     4.1. MIPI A-PHY SerDes (Physical Layer and Data Link Layer)
          4.1.1 A-PHY Overview
          4.1.2. A-PHY Performance
          4.1.3 A-PHY Future Enhancements
          4.1.4 A-PHY Adoption as an IEEE Standard
     4.2. A-PHY Protocol Adaptation Layers (PALs)
     4.3. MASS Protocol Layer
          4.3.1 MIPI Camera Protocols
          4.3.1.1 MIPI CSI-2
          4.3.1.2 MIPI Camera Service Extensions (CSE)
          4.3.1.3 MIPI Camera Command Set (CCS)
          4.3.2 Display Protocols
          4.3.2.1 MIPI DSI-2
          4.3.2.2 MIPI Display Service Extensions (DSE)
          4.3.2.3 MIPI Display Command Set (DCS)
          4.3.2.4 VESA Display Protocols
     4.4. Functional Safety
     4.5. Security
     4.6. Conformance Test Suites for MASS Specifications
5. Conclusion
Annex A. MASS Use Case Examples
    A.1. Example 1: Rear Backup Camera with Dashboard Display
    A.2. Example 2: Lane-Keeping Cameras

 

1. Executive Summary

In Brief

MIPI Automotive SerDes Solutions (MASS) is a family of specifications that establishes a full stack, ultra- reliable in-vehicle connectivity framework for high-performance sensors and displays. Encompassing a standardized long-reach SerDes (MIPI A-PHY) and proven higher-layer protocols for cameras, sensors and displays (such as MIPI CSI-2, MIPI DSI-2 and VESA eDP/DP), with functional safety and security enablers built in, MASS is a key facilitator for advanced driver-assistance systems, digital cockpits and in-vehicle infotainment services.

 

 

Automotive systems are currently undergoing an accelerated evolution due to disruptive industry trends in connectivity, automation, sharing and electrification (known as “CASE”). Advanced driver-assistance systems (ADAS), digital cockpits, in-vehicle infotainment (IVI) and autonomous driving systems (ADS) are driving a rapid proliferation of in-vehicle sensors and displays, and need for ever-increasing camera and display resolutions, frame rates and bit-depths. The resultant multi-gigabit net data throughputs required to connect all of these vehicle sensors and displays presents a significant design issue for future vehicles, requiring the development of innovative electrical and electronic (E/E) architectures that leverage the latest high-speed automotive networking protocols.

MIPI White Paper: Introductory Guide to MASS - Figure 1

Figure 1 Automotive industry trends defined as “CASE.” (Source: MIPI Alliance)

To overcome these challenges and support new architectures, MIPI Alliance has developed MIPI Automotive SerDes Solutions (MASS) – an end-to-end framework for connecting cameras, sensors and displays using MIPI A-PHY, MIPI CSI-2, MIPI DSI-2 and many other de facto industry standardized protocols, with functional safety, security and resilience built in.

Representing a collaborative cross-industry effort to meet the needs of the automotive industry, MASS consists of four principal components that, when combined together, create this complete end-to-end connectivity framework:

  • SerDes physical layer. The foundation of MASS is MIPI A-PHY, the first industry-standard, long-reach, asymmetric, serializer/deserializer (SerDes) physical layer interface with high noise immunity. A-PHY is designed specifically to meet the needs of the automotive industry and will eliminate the need for proprietary asymmetric PHYs and bridges, simplifying in-vehicle communication networks and reducing cost, cable harness weight and development time.
  • Higher-layer protocols. MASS incorporates a suite of widely adopted higher layer application protocols used in billions of devices and becoming leveraged in automotive. These protocols include MIPI CSI-2 for cameras, MIPI DSI-2 and VESA eDP/DP for displays, and lower speed protocols such as I2C (Inter-Intergrated Circuit), GPIO (General Purpose Input Output), Ethernet and MIPI I3C®. Use of these widely adopted protocols will drive economies of scale, reduce NRE/development cost and provide backward and forward compatibility.
  • Functional safety. MASS standardizes several functional safety enabling features, helping MASS-based applications meet the functional safety requirements of ISO standard 26262:2018 “Road vehicles – Functional safety” and enabling designers to build systems that meet common Automotive Safety Integrity Level (ASIL) specifications, from ASIL B through ASIL D.
  • Security. MASS also includes security enabling functionality. High-bandwidth Digital Content Protection (HDCP) is already supported for display applications, and additional security enabling functionality to enable end-to-end authentication, privacy (encryption), message integrity and replay protection will be added in the near future.

All of MIPI’s baseline MASS specifications have either already been completed, or are nearing completion by the end of 2021. Additional specifications and updates to add further security enablers to the MASS framework will be completed in mid-2022.

This white paper provides an introduction to automotive market trends, an overview of the MASS framework and its components and example MASS use cases. For more information please visit https://mipi.org/automotive.

2. Overview of Automotive Market Trends and Challenges

Automotive sensor (camera/lidar/radar) and display systems are undergoing accelerated evolution driven by the disruptive industry trends of connectivity, automation, sharing and electrification. This combination of trends, described in Table 1, is driving an increasing number of external sensors and in-cabin automotive displays, examples of which are shown in Figure 2.

MIPI White Paper: Introductory Guide to MASS - Table 1

Table 1 CASE: Driving the proliferation of in-vehicle sensors and displays (Source: MIPI Alliance)

 

MIPI White Paper: Introductory Guide to MASS - Figure 2a

 

MIPI White Paper: Introductory Guide to MASS - Figure 2b

Figure 2 Example proliferation of external vehicle sensors and in-vehicle displays (Source: MIPI Alliance)

These trends are backed up by market research that predicts rapid growth in the number of vehicles supporting ADAS features in the next decade. The data shows that the complexity of ADAS systems will increase rapidly, driving market adoption of vehicles supporting SAE autonomy levels 1, 2, 3 and above, as shown in Figure 3.

MIPI White Paper: Introductory Guide to MASS - Figure 3

Figure 3 Market forecast by level of autonomy (Source: Yole Développement)

The proliferation in the number of vehicle sensors and displays is also combined with the growing data payload demands driven by ever-increasing camera and display resolutions, frame rates and bit depths. The results of a study, conducted by MIPI in 2018 to forecast the data bandwidth demands of camera and display modules, is shown in Figure 4. This information was used to identify the initial MASS SerDes target speed of 16 Gbps.

MIPI White Paper: Introductory Guide to MASS - Figure 4

Figure 4 Increasing display and camera data payloads (Source: MIPI Alliance)

3. Introduction to MIPI Automotive SerDes Solutions (MASS)

To support the development of new electrical and electronic (E/E) architectures that overcome the challenges described in the previous section, MIPI Alliance has developed MIPI Automotive SerDes Solutions (MASS) – an end-to-end framework for connecting cameras, sensors and displays within vehicles using MIPI A-PHY, MIPI CSI-2, MIPI DSI-2 and many other de facto industry standardized protocols with functional safety, security and resilience built in.

Prior to MASS, the automotive industry has had to rely on proprietary SerDes protocols for long-reach links between peripheral components and processors, and has had to design proprietary functional safety solutions. This lack of standardization and supporting connectivity framework has limited supplier choice, prohibited economies of scale and increased design complexity and cost.

The MASS framework leverages existing MIPI protocols that have already been widely implemented in automotive, as well as other protocols, such as VESA’s DisplayPort (DP) and embedded DisplayPort (eDP) for displays, and numerous supporting protocols such as I2C and GPIO.

MIPI White Paper: Introductory Guide to MASS - Figure 5

Figure 5 End-to-end MASS system diagram (Source: MIPI Alliance)

MASS creates economies of scale around a set of industry-supported standards, reducing integration costs and enabling automotive original equipment manufacturers (OEMs) and Tier 1 suppliers to amortize engineering costs over larger volumes of components. It also promotes the development of enhanced support services such as test and software resources from a wide ecosystem of industry contributors.

Standardization also helps industry improve technologies more quickly, as vendors develop more efficient ways to implement these specifications – which are then integrated into future releases. Standardized interfaces can also ease ongoing product maintenance and updates, thanks to backward and forward compatibility, while also encouraging long-term developer support.

Use of standards removes the burden of designing or selecting a proprietary interface, allowing OEMs and Tier 1 suppliers to focus on “higher value” product differentiating technologies that sit higher up the protocol stack – such as applications that leverage machine learning and artificial intelligence to provide enhanced customer experiences.

MASS is purpose-built to address applications that require high-speed, highly asymmetric data links within a vehicle. It complements symmetric protocols such as automotive Ethernet. While Ethernet and other symmetric network protocols are primarily designed for full duplex, symmetric networking among peer devices, MASS is optimized to link resource-constrained peripheral components with their associated electronic control units (ECUs). Use of MASS means that components at the edge of a vehicle can be smaller and less complex while providing high bandwidth in one direction, such as an inbound data stream from a camera or lidar sensor to an ECU, or an outbound data stream from an ECU to a digital cockpit display.

Roadmap to Integration

MASS is designed for immediate implementation. As shown in Figure 6, initial implementations will see standardized A-PHY SerDes bridges extend the range of short distance MIPI C-PHY/ D-PHY physical interfaces – replacing proprietary long distance SerDes solutions.

MIPI White Paper: Introductory Guide to MASS - Figure 6

Figure 6 MASS bridge solution vs. MASS integrated solution (Source: MIPI Alliance)

MASS implementations will become more streamlined with the integration of A-PHY and other MASS protocols directly into sensors, ECUs and displays - eliminating the need for separate bridge components. In some cases, integration may happen first in one end of the A-PHY link or the other, such as integration into the graphics processor first, before integration into the display module.

4. The MASS Framework

MASS consists of four principal components which, when combined, create an end-to-end automotive connectivity framework. The four components are (1) the physical layer interface, (2) higher-layer protocols, (3) functional safety and (4) security. Each component is described in more detail in Table 2.

MIPI White Paper: Introductory Guide to MASS - Table 2

Table 2 Principal components of MASS (Source: MIPI Alliance)

To illustrate how these specifications form the framework, the full MASS protocol stack is shown in Figure 7, encompassing physical and link layers, protocol adaptation layer and protocol layer.

MIPI White Paper: Introductory Guide to MASS - Figure 7

Figure 7 MASS protocol stack (Source: MIPI Alliance)

MIPI White Paper: Introductory Guide to MASS - Table 3

Table 3 MASS specifications (as of June 2021) (Source: MIPI Alliance)

The specifications that presently make up each layer in the MASS framework are listed in Table 3, and each specification is described in more detail below. An overview of the functional safety and security enabling functionality built into MASS, and a short description of the various conformance test suites that support the specifications, are also provided.

The majority of the MASS specifications have been completed, with remaining core specifications nearing completion by the end of 2021. Additional specifications to add further security enablers to the MASS framework will be completed in mid-2022.

4.1. MIPI A-PHY SerDes (Physical Layer and Data Link Layer)

In September 2020, MIPI Alliance released MIPI A-PHY v1.0, the first asymmetric industry-standard, long-reach SerDes physical layer interface. A-PHY is designed to meet the specific needs of the automotive industry and will eliminate the need for proprietary PHYs and bridges, simplifying in-vehicle communication networks and reducing cost, weight and development time.

In addition to the benefits of standardization, A-PHY offers unprecedented resiliency and reliability, and allows OEMs, Tier 1 suppliers and component vendors to simplify and streamline camera, sensor and display integration. A-PHY extends the use of MIPI CSI-2 and MIPI DSI-2, as well as other approved non-MIPI upper-layer protocols, which can decrease design complexity and accelerate time to market.

4.1.1. A-PHY Overview

The A-PHY physical interface, shown in Figure 8, provides an asymmetric data link between data source and data sink in a point-to-point or daisy-chain topology that includes high-speed unidirectional data, embedded bidirectional control data and optional power delivery over a single cable (coaxial or shielded differential pair).

MIPI White Paper: Introductory Guide to MASS - Figure 8

Figure 8 A-PHY physical interface (Source: MIPI Alliance)

A-PHY’s primary mission in the automotive system is the transfer of data between cameras and displays and their corresponding ECUs. A-PHY provides a protocol-agnostic data link layer that enables support for other MIPI specifications and MIPI-approved third-party specifications. With a range of up to 15 meters, it allows higher-layer protocols like MIPI CSI-2 and MIPI DSI-2 to operate directly over a physical link spanning an entire vehicle.

Key features of A-PHY v1.0 are:

  • Data rates as high as 16 Gbps in A-PHY v1.0, 32 Gbps in v1.1, and a roadmap to 48 Gbps and beyond
  • High reliability, with an ultra-low packet error rate (PER) of <10-19 for the lifetime of a vehicle
  • High resiliency, with ultra-high immunity to EMI effects
  • Low latency (maximum 6 microseconds)
  • Support for multiple cable types – coaxial and shielded differential pair (SDP)
  • Up to 15 meters in length with four inline connectors

4.1.2. A-PHY Performance

A-PHY v1.0 defines two profiles and five speed gears (shown in Table 4) to meet the performance, cost and complexity requirements of a broad range of different applications.

MIPI White Paper: Introductory Guide to MASS - Table 4

Table 4 A-PHY v1.0 speed gears and modulation (Source: MIPI Alliance)

The profiles and gears are:

  • Profile 1: Designed for simple, lowest-cost implementations and reduced time to market, and uses NRZ-8b10b encoding. It forms the basis of gears G1 and G2.
  • Profile 2: Designed for high-performance applications, uses pulse-amplitude modulation (PAM) encoding, and has higher EMC immunity and a lower packet error rate. It forms the basis of gears G3, G4 and G5, as well as future, higher-speed gears.

The speed gears meet the requirements for connecting high-performance cameras, sensors and displays. For example Gear 5, which supports 16 Gbps, can stream video in Ultra-HD 3840x2160 resolution at 60 frames per second. A-PHY also meets latency requirements for safety applications: In Gear 5, A-PHY v1.0 operates with a maximum of 6 microseconds of latency between the generation of a packet in the A-PHY transmitter and the reception of a packet in the A-PHY receiver. It is in this time period where rapid PHY- level retransmissions can occur to deliver the ultra-low packet error rate, as described below.

MIPI White Paper: Introductory Guide to MASS - Figure 9

Figure 9 A-PHY Protocol Adaptation Layer (Source: MIPI Alliance)

 

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 for MIPI CSI-2 and MIPI DSI-2, additional PALs are being developed for several low- bandwidth control interfaces as described in section 4.2.

A-PHY includes Narrow Band Interference Cancellation (NBIC) and a PHY-level retransmission scheme (RTS) for maximum link reliability and ultra-low packet error rate. The RTS provides ultra-high immunity to EMI effects, recovering damaged A-Packets and ensuring a steady link. MIPI Alliance testing at an independent lab has shown that A-PHY connections can retain a high level of immunity, even after years of mechanical stress and aging. This contributes to A-PHY’s ultra-low packet error rate of <10-19 – or less than one packet error over the lifetime of a vehicle.

4.1.3. A-PHY Future Enhancements

A-PHY v1.1, already in development, will double the maximum downlink data rate in Gear 5 from 16 Gbps to 32 Gbps by supporting dual downlinks over star quad (STQ) cables. It will also double the uplink speed from 100 Mbps to 200 Mbps. In addition, A-PHY v1.1 will expand PAM4 encoding to lower gears (G1 and G2), reducing the operating bandwidth of these gears to allow OEMs, Tier 1s and suppliers to implement A-PHY using lower cost legacy cables and connectors.

4.1.4. A-PHY Adoption as an IEEE Standard

A-PHY v1.0 has been adopted as an IEEE standard. The approval of IEEE 2977™-2021, “IEEE Standard for Adoption of MIPI Alliance Specification for A-PHY Interface (A-PHY) Version 1.0”, expands the ecosystem of application expertise around MIPI A-PHY and, in turn, further promotes interoperability, vendor choice and economies of scale for the global automotive industry.

4.2 A-PHY Protocol Adaptation Layers (PALs)

MIPI PALs Define the adaptations necessary to carry proven MIPI and approved third-party protocols over A-PHY links. The MIPI PALs map those approved higher-layer protocols to A-PHY’s A-Packet format, acting as a conduit to and from A-PHY’s generic data link layer (see Figure 9). In this way, the PALs enable the higher-layer protocols to operate seamlessly over A-PHY physical links.

MASS incorporates multiple PAL specifications to simplify the integration of A-PHY with a variety of upper-layer protocols. PALs for MIPI CSI-2, MIPI DSI-2, VESA eDP/DP, I2C and GPIO interfaces are already available. An additional PAL to enable the control and configuration of peripheral devices via Ethernet is currently in development and planned for release in 2021. Further, a PAL for I3C is slated for development in 2022. A full list of PALs is provided in Table 5.

MIPI White Paper: Introductory Guide to MASS - Table 5

Table 5 MASS protocol adaptation layers (Source: MIPI Alliance)

4.3. MASS Protocol Layer

MASS leverages a suite of widely adopted higher-layer protocols that are already widely supported within the automotive industry, such as MIPI CSI-2 for cameras, MIPI DSI-2 and VESA eDP/DP for displays, and numerous lower speed control protocols such as I2C, GPIO, Ethernet and I3C. A brief overview of each higher-layer protocol is provided here.

4.3.1. MIPI Camera Protocols

MIPI’s camera interfaces interconnect cameras and other high-speed sensors to application processors or image signal processors. The protocols are used to bring high-resolution imaging, rich color and advanced imaging capabilities to smartphones, tablets, automobiles, drones, wearables and other products. The most widely adopted protocol is MIPI Camera Serial Interface 2 (CSI-2), which for automotive applications is augmented with MIPI Camera Service Extensions (CSE) for safety and security, and MIPI Camera Command Set (CCS) for higher-layer control.

4.3.1.1. MIPI CSI-2

CSI-2 has been used to connect cameras with host devices in mobile systems since 2005. In addition to its ubiquity in mobile devices, CSI-2 is widely used in automotive system-on-chip (SoC) components, providing connections not just to onboard cameras but also to CSI-2-based radar and lidar sensors that play critical roles in ADAS. This widespread adoption is a testament to both the ongoing evolution of CSI-2 and its flexibility to serve many applications, as well as the reliability and maturity of the specification to service automotive-grade electronics systems.

CSI-2 can support sensors that have a broad range of different image resolutions, video frame rates, color depths and high-dynamic-range capabilities. For example, current applications use camera resolutions of more than 40 megapixels and video capture rates of more than 4K/120fps or 8K/30fps. This makes CSI-2 ideal for use in today’s vehicles, which require many cameras and other sensors, each with its own purpose and requirements.

CSI-2 v3.0 comes with features designed specifically for modern vehicle imaging systems that make use of machine awareness, such as:

  • RAW-24: A format for representing individual image pixels with 24-bit precision. This provides higher image quality that helps self-driving systems make better decisions. For example, when designing an ADAS application RAW-24 can help a front-facing camera system to distinguish between a shadow and a dark obstacle on the road, even when the car has just gone from bright sunlight into a tunnel.
  • Smart Region of Interest (SROI): A feature for better analyzing images using machine inferencing algorithms. This may mean performing more analysis in the sensor module while sending less data to a remote ECU.
  • Unified Serial Link (USL): A feature for reducing the number of wires linking an image sensor with a companion application processor by encapsulating control signaling data with imaging pixels. Fewer wires make it easier to link an onboard sensor to a processor while reducing design complexity.

CSI-2 v4.0 will be released in 2021, adding support for:

  • Always-On Sentinel Conduit (AOSC): A feature enabling ultra-low-power, always-on inferencing by integrated or external controllers, allowing a low-power sensor to be always on, always monitoring its surrounding environment and waking a remote application CPU only when a relevant event happens. AOSC will enable CSI-2 frame transport and bidirectional control over a two-wire I3C solution, as opposed to nominal transport over a CSI-2 PHY such as MIPI C-PHY or MIPI D-PHY.
  • RAW-28 image capture: A feature for mission-critical, real-time perception autonomous applications.

4.3.1.2. MIPI Camera Service Extensions (CSE)

The Camera Service Extensions (CSE) specification defines extended functions for CSI-2, including functional safety, security and other features. The CSE specification can be used in automotive systems with functional safety goals from ASIL B through to ASIL D. The use of CSE is also applicable for non-automotive use cases.

CSE defines a Service Extensions Packet (SEP) format to enable end-to-end data protection mechanisms from a sensor to its associated ECU. All SEP packets are tunneled over MIPI C-PHY / MIPI D-PHY when connecting using SerDes bridges, then further tunneled via the A-PHY bridge to the far-end A-PHY receiver.

CSE defines also the ESS-CCI (Enhanced Safety and Security for Camera Command Interface) protocol to enable end-to-end protection of the control channel between the sensor and its associated ECU. The ESS- CCI protocol is tunneled over A-PHY using the PAL/I2C.

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

If all components in the system (i.e., the data source and data sink) support CSE, then any SEP packets created by the source (e.g., an image sensor) and transported to the sink (e.g., an image processor) that are modified or disrupted along the way will be detected.

4.3.1.3. MIPI Camera Command Set (CCS)

The MIPI Camera Command Set (CCS) is designed for use with CSI-2 and enables the rapid integration of image sensor functionalities without device-specific drivers. It also gives developers the flexibility to customize their implementations for more advanced camera and imaging systems, and to reduce the integration requirements and costs that come with deploying camera and imaging components.

CCS provides support for CCS Static Data to standardize capability and configuration files, and can be used with sensors supporting I2C, MIPI I3C and MIPI CSI-2’s Unified Serial Link (USL) command and control interfaces. Using CCS Static Data, one device driver can interact with many different image sensors and modules, making it possible to have one common driver, simplifying the integration of new components.

MIPI also provides CCS Tools to complement CCS by providing:

  • A definition of a plain-text format, based on YAML, that lets developers read and edit CCS Static Data files in text and can be easily produced by scripts and other programs.
  • A Perl script, to convert those text-based CCS Static Data files to the CCS Static Data binary format.
  • A reference library implementation, written in C, that provides a common tool for parsing the binary files the converter produces, making it easier to support CCS Static Data in drivers. It ensures that CCS Static Data binaries are read the same way wherever the standard parser library is used.

In addition, a Linux driver for CCS-compliant camera sensors has been developed for inclusion in the Linux mainline kernel. MIPI CCS and MIPI CCS Tools are publicly available.

CCS Tools is distributed under the 3-Clause BSD License and is available for download in the MIPI Alliance GitHub repository.

4.3.2. Display Protocols

4.3.2.1. MIPI DSI-2

The DSI-2 specification is already equipped to support multiple in-vehicle displays, thanks to the high-bandwidth physical link, data compression and a flexible yet simple architecture. With support for custom as well as standard designs, DSI-2 is well-suited for the new wave of automotive display developments. The core DSI-2 specification is augmented with the MIPI DSE and DCS specifications (detailed below).

Like CSI-2, the DSI-2 specification was initially developed for smartphones in the mid-2000s, supporting high resolutions and frame rates with low power consumption to service both display mode and command mode displays. DSI-2 can support more than three gigapixels per second of uncompressed image content today, doubling to six gigapixels in the recently released v2.0 specification. Its transport layer incorporates the VESA VDC-M standard for visually lossless compression of display payloads.

DSI-2 allows designers to daisy-chain several displays, each with different pixel timing, across the same console using one set of signal wires. Its command protocol (MIPI DCS) ensures that each display receives data packets timed to its own refresh rate, while MIPI PHYs with fewer wires mean a reduction of components, lower system and manufacturing cost, and lower complexity.

The DSI-2 protocol supports features to meet stringent requirements unique to the automotive industry, including enhanced link integrity for safety applications and HDCP to keep entertainment streams secure.

Use of image compression is essential to address the proliferation of high-performance and high interface speed displays in next-generation vehicles. The VDC-M display compression standard achieves a maximum compression ratio of 6:1, such as reducing a 24-bit uncompressed source RGB pixel to 4 bits per pixel (or 30- bit uncompressed source RGB pixel to 5 bits per pixel) when compressed with minimal impact on latency, which can help automotive designers to meet the demand for greater total vehicle display bandwidth.

MIPI recently undertook an image compression study to evaluate the visually lossless properties of VDC-M for automotive use cases. The study concluded that automotive images compressed using the VDC-M standard met the objective of being visually lossless, thus demonstrating that DSI-2 offers a solution to the growing bandwidth challenges in next-generation vehicles and can reduce interface speeds by the above 6:1 reduction factor. The paper can be downloaded from the MIPI Alliance website.

4.3.2.2. MIPI Display Service Extensions (DSE)

The Display Service Extensions (DSE) specification defines flows and mechanisms that enable the DSI-2 and eDP/DP display protocols to be carried over A-PHY links between a display source, such as a central ECU, and a display sink, such as an active-matrix display module. DSE enables functional safety, security and other features.

DSE defines a Service Extension Packet (SEP) format both to enable data protection and to embed video timing and clock information into A-PHY packets. Display stream content is converted to/from the SEP format by the display source and sinks at their protocol layers, providing end-to-end data protection.

In the case of an A-PHY bridge implementation, SEP packets are tunneled over MIPI C-PHY / MIPI D-PHY from the data source to an A-PHY SerDes bridge component. Here they are packetized into A-PHY A-Packets and tunneled over the packet-switched A-PHY network to a far-end receiver where the reverse operation takes place. Where a display source and/or sink component supports integrated A-PHY capabilities, SEP packets can be directly tunneled via the A-PHY network to a far-end A-PHY receiver without the need for bridge components.

Use of the SEP format enables a display system to fulfill ADAS safety goals up to ASIL D level (per ISO 26262:2018) and supports safety mechanisms, including end-to-end protection as recommended for “high” diagnostic coverage of the data communication bus.

If all system components (i.e., the data source and data sink) support DSE, then any SEP packets created by the source and transported to the sink that are modified or disrupted along the way will be detected.

4.3.2.3. MIPI Display Command Set (DCS)

The Display Command Set (DCS) specification provides a standardized command set for display control functions and the supply of image data to displays over DSI-2. It defines commands for all setup, control and test functions, including the control of settings such as resolution, width and brightness. DCS supports the VESA DSC and VDC-M display stream compression standards.

Implementing the DCS specification reduces the time-to-market and design cost of mobile devices and other products by simplifying the interconnection of products from different manufacturers. It also simplifies the addition of new product features, such as larger or additional displays, due to the extensible nature of MIPI specifications.

4.3.2.4. VESA Display Protocols

VESA DisplayPort and Embedded DisplayPort (eDP) are digital display protocols developed and standardized by VESA. The interface is primarily used to connect a video source (e.g., ECU) to a display device (e.g., display module).

4.4. Functional Safety

MASS provides functionality to enable data protection, helping MASS-based applications meet the functional safety requirements of ISO 26262:2018 and enabling designers to build systems that meet the single point fault metric (SPFM) and latent fault metric (LFM) as defined in the respective ASIL specifications, from ASIL B through ASIL D.

MIPI White Paper: Introductory Guide to MASS - Figure 10

Figure 10 Example of “bridge-to-bridge” and ”end-to-end” data protection (Source: MIPI Alliance)

Several features are built into MASS at both physical and protocol layers to enable data protection within a “bridge-to-bridge” and “end-to-end” solution as shown in Figure 10.

At the physical layer, A-PHY contains features to enable functional safety within automotive applications:

  • A-PHY’s A-Packet format includes cyclic redundancy checks (CRCs) in both the packet header and the packet footer, an 8-bit message counter in the header to detect loss of A-Packets and replay attacks, and a timeout monitor to detect loss of communication.
  • A time-bounded PHY-level local retransmission scheme (RTS) for each A-PHY link recovers damaged A-Packets for a steady connection, completely transparently to the upper protocol layers. The RTS provides ultra-high immunity to EMI effects, and the low overhead of the RTS contributes to A-PHY’s approximately 90 percent efficiency in the upper gears 3, 4 and 5 – a higher efficiency than many other protocols can achieve.

Higher up in the MASS stack, the pair of service extension specifications (MIPI CSE and MIPI DSE) add functional safety to higher-layer camera and display protocols. This enables “end-to-end” data protection from sensor data source to ECU data sink (including optional transport through bridges), and likewise from ECU data source to display panel data sink (including optional transport through bridges). More information on CSE and DSE can be found above in sections 4.3.1.2 and 4.3.2.2, respectively.

4.5. Security

MASS incorporates security features. The initial release of MIPI DSE supports HDCP for displays, providing end-to-end content protection for MIPI DSI-2 display data and bridge-to-bridge data protection for VESA eDP/DP display data.

Additional security functionality will be added to the next releases of the CSE and DSE specifications in mid-2022. These updates will add end-to-end security enablers, including authentication, confidentiality (encryption), data integrity and replay protection.

4.6. Conformance Test Suites for MASS Specifications

MIPI Alliance has developed Conformance Test Suites (CTSs) to ensure the interoperability of MIPI specification-based products and the availability of test tools and environments. The test suites have been developed to help implementers evaluate the conformance of their products. It is important to recognize that MIPI does not approve or certify that any products are in compliance with its specifications, and does not currently define an official qualification program.

Conformance test suites for C-PHY, D-PHY and CSI-2 are presently available to MIPI members. A conformance test suite for CCS is publicly available (for members and non-menbers) on the MIPI website.

Test suites for A-PHY, DSI-2 and DCS are under development.

5. Conclusion

Today, automotive technology is advancing faster than ever, and electronic components have never been more central to the design and success of new vehicles. Advanced driver-assistance systems (ADAS) and rapidly evolving in-vehicle infotainment (IVI) platforms are the stars of many new models, while autonomous driving systems (ADS) are a major focus of development. These innovations require more cameras, sensors, displays and computing resources from a growing ecosystem of suppliers. The data interfaces linking components together play an essential role in safety and security, which are core requirements of the new onboard systems. Standardization and its promise of interoperability are essential for automotive innovation to flourish.

MIPI Alliance is addressing these applications with MIPI Automotive SerDes Solutions (MASS), an end-to-end, full stack of connectivity solutions for the growing number of cameras, sensors and displays that enable automotive applications. These solutions, with unprecedented functional safety and security built in at the protocol level, will help automakers integrate new and emerging safety features such as low-latency backup cameras, lane-keeping and sign-detection sensors and 360-degree camera, lidar and radar systems. MASS also supports the integration of multiple high-resolution instrumentation, control and entertainment displays.

Annex A - MASS Use Case Examples

A.1. Example 1: Rear Backup Camera with Dashboard Display

MIPI White Paper: Introductory Guide to MASS - Figure 11

Figure 11 Example use case: Rear backup camera and display (Source: MIPI Alliance)

A rear-mounted camera aimed behind the vehicle provides real-time video to a high-definition display, alerting the driver to pedestrians or other objects in the car’s path. The camera streams image data, using MIPI CSI-2 over MIPI A-PHY, directly to an ECU. After the ECU processes the data, it transmits a real-time video stream to a display on the driver’s dash, using either MIPI DSI-2 or VESA eDP/DP directly over MIPI A-PHY.

A.2. Example 2: Lane-Keeping Cameras

MIPI White Paper: Introductory Guide to MASS - Figure 12

Figure 12 Example use case: Lane-keeping cameras/sensors (Source: MIPI Alliance)

High-resolution MIPI CSI-2 cameras and other sensors are mounted in the front of the car to capture real- time images of road markings. In some cases, the camera/sensor module may do some pre-processing to determine the car’s position within a lane. Image data is transferred from the camera/sensors to an ECU using MIPI CSI-2 over MIPI A-PHY. The ECU takes in data from multiple cameras/sensors and performs sensor fusion to enable advanced driver assistance systems and real-time decision-making.

In both configurations shown in Figure 12, functional safety and security functions are implemented from data source to data sink to ensure an ultra-low error rate and end-to-end protection against intentional or unintentional tampering. These closed-loop MASS implementations ensure the image sensors and/or displays work reliably, which is especially important for these types of safety-critical use cases. In both configurations, A-PHY’s low latency and high data rate enable high-quality image transfers under strict timing requirements.