What is Mobile Industry Processor Interface (MIPI) Protocol? 

Licinio Sousa

Mar 16, 2022 / 6 min read

Grand visions surround cars of the future, putting a spotlight on the technologies that will power them. Today, sensors are vital to the next phase of automotive vision and safety, as drivers and passengers depend on them. They enable numerous applications, often artificial intelligence (AI)-based, including advanced driver assistance systems (ADAS) encompassing automatic emergency braking, lane keeping, surround view, and, ultimately, autonomous driving. Waymo’s autonomous system for robotaxis, for instance, uses up to 29 image sensors while a typical consumer AV system might use anywhere between 10 and 20.

System-on-chip (SoC) requirements for new and complex automotive electronics now leverage more displays and sensors, including imaging, LiDAR, radar, ultrasound, and infrared technologies.

Embedded display innovations continue to be driven by the mobile and automotive markets. In fact, higher resolutions, 120+ Hz refresh rate, and foldable displays are already being deployed to customers. These shifts have highlighted the value and technical advantages of interfaces such as the mobile industry processor interface (MIPI) protocol. The success of MIPI protocols for mobile is now extending to automotive applications and helping to meet specific automotive camera and display requirements.

Read on to learn more about the new electronics architecture required to meet these growing demands and current market dynamics, as well as the role of MIPI interfaces in automotive, how to address automotive IP and SoC functional safety requirements, and the need to design for reliability going forward.

Connected Cars at an Intersection

Speeding Toward Centralization

In the past, distributed electronic control units (ECU) were the name of the game in the automotive world; each ECU implemented a specific application. In the world of domain-based applications, each application, such as ADAS or infotainment, is executed in an independent domain ECU.

Centralizing multiple applications on a single domain controller increases the performance requirements to implement those applications. Yet here too things are evolving; we are already moving toward a zonal architecture, which will enable applications to become more centralized. Volkswagen has made it clear that it sees this trend as a key part of its zonal architecture transition. This move promises to simplify the in-car network, while also adding complexity to SoC implementation.

Vehicle designs are increasingly combining different sensors to maximize their respective advantages and offset their shortcomings. For example, an automatic emergency braking application needs to be able to identify objects in the road, be it a pedestrian, a bicycle, or the shadow from a passing cloud. This pushes performance requirements up to 1,000 tera operations per second (TOPS) — reflecting heavy processing demands.

MIPI Protocol: The Great Connector

Such an advancement would not be possible without the MIPI protocol. The MIPI Alliance offers a portfolio of display and camera interfaces that differentiates a wide range of capabilities, from basic connectivity to complex multiple-image sensor and display connectivity, all while addressing fundamental requirements such as bandwidth, power, and implementation cost. By implementing these specifications, the automotive industry can take advantage of economies of scale, while reducing costs and enabling higher performance.

The MIPI protocol is what allows the connection between sensors and application processors. The image sensors that provide the car’s surrounding view need to capture many different scenes, from extreme light to dark to flickering LEDs. To make sense of those scenes and optimize the vehicle’s performance and safety, the data from image sensors needs to be combined with other sensor data. For example, thermal, radar, and ultrasound sensors can all help in blind spot detection; together, image, thermal, and radar sensors offer more robust collision avoidance than an image sensor alone. With more sensor data comes more opportunities for sensor fusion and, as a result, more specialized capabilities for the user.

The MIPI Camera Serial interface 2 (CSI-2) allows for sensor fusion. This technology has been deployed in billions of mobile units around the world. While a proven technology in the mobile arena, it was also conceived as a vision platform for applications beyond handheld devices. The MIPI CSI-2 is optimized for imaging applications and enables low power, which becomes essential for the automotive industry considering the number of sensors likely to be used concurrently in any given vehicle.

MIPI Protocol Features | Synopsys

Over the years, the MIPI CSI-2 protocol has evolved to add more capabilities, including virtual channels, which identify payloads coming from different sources. Virtual channels are important for applications like ADAS where multiple image sensors are used or any application where it is important to distinguish multiple exposures from the same sensor.

The faster an application can capture an image or process information, the more rapidly it can make decisions — such as when to apply the brakes. As the megapixels in image sensors increase, so does the necessary bandwidth. MIPI physical layers (PHY) can support this growth: a four-lane D-PHY v2.1 port can accommodate 18 gigabits per second (Gbps), while a C-PHY v2.0 can handle up to 44.5 Gbps, offering high speed with low power and pin count.

New Levels of Automotive Safety

The MIPI Alliance is focused on addressing automotive regulations and as such has upgraded the MIPI protocol to align with the ISO 26262 standard for functional safety. CSI-2 version 4.0 carries added safety features centered on robustness of transmission. This means being able to identify if a pixel is dropped and act to rectify it, which is critical in the context of a moving vehicle that is reliant on the accuracy of its sensor data.

MIPI D-PHY implementation showing dedicated clock lanes next to data lanes

We are also seeing the components themselves become more robust. The automotive industry requires components to last for 15 years, or a typical vehicle’s lifetime, and be able to withstand extremes of temperature and vibration. The ISO 26262 standard has heightened the safety bar for the development process of automotive devices. This means creating a safety plan upfront that defines the goals and requirements the team must execute, putting those features in place, and analyzing them to ensure they are compliant. The AEC-Q100 standard has also raised the bar for the development, defining levels of quality and reliability that an automotive device, including the IP and SoC, must pass.

The Need for a Comprehensive Automotive-Grade MIPI IP

At the SoC level, ISO 26262 also requires a higher level of implementation. One way to achieve this is make the safety manager processor independent of the application processors. Setting up dedicated implementation of safety management means automakers can monitor and react to the safety states of all the SoC components in real time.

As an SoC designer, one also needs to factor in the impact of harsh conditions — particularly in extreme temperatures — that the various components are expected to withstand as they perform. Just as IP design requires a holistic perspective, so does the SoC. Considerations on your next project will include determining the best interface for input, the number of ports needed, protocol support, CSI-2 and DSI/DSI-2 support, the right combination of D-PHY and C-PHY, and so forth. It is a complete package designed to uphold the three automotive pillars of safety, reliability, and quality.

MIPI has the power to reduce complexity as well as make way for critical safety applications. At Synopsys, we enable the integration of MIPI interfaces that support C-PHY, D-PHY, CSI-2, and DSI/DSI-2. Synopsys DesignWare® MIPI® IP solutions enable the interface between SoCs, application processors, baseband processors, and peripheral devices. The IP supports the latest key features of the MIPI specifications, such as C-PHY 2.0 operating at 6.5Gs/s per trio at maximum bandwidth of 41Gb/s. Synopsys’ MIPI camera and display IP are automotive-grade in accordance with the ISO 26262 standard. In addition, Synopsys IP is designed and tested for AEC-Q100 reliability.

As a prominent member of the MIPI Board of Directors and an active contributor to the MIPI Alliance working groups, we continue to support the ecosystem by developing high-quality, low-power, cost-effective, interoperable MIPI IP solutions that enable designers to deploy new features in their automotive designs. Utilizing a single-vendor solution allows designers to lower the risk and cost of integrating MIPI interfaces into SoCs and device ICs, while speeding time-to-market.

With the increasing data required for high-resolution videos and images, cameras and display SoCs will need to process more complex visual data in the coming years. As industries grapple with more image data, especially for automotive applications, MIPI will provide a solution for the “long-reach, high-speed challenge” of connecting the highest speed electronic components throughout a vehicle.

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