MOST150 enables New Features in the Infotainment System
Meanwhile, the work is continually going on and new features will be defined in the coming MOST Specification Rev. 3.1. One of these features is a multiport network interface controller that is able to allocate the true, full bandwidth of up to 150 Mbit/s in up to eight branches. This enables a streaming bandwidth of up to 1.2 Gbit/s and allows a variety of topologies. In addition, a remote network interface controller has been defined in a MOST network. It works autonomously without the need for a host controller, thus enabling the concentration of software in a centralized unit and tremendously simplifying the complexity of the "remote" nodes. Beyond, this article will show the evolution of the application framework based on new data types and a new xml schema based exchange format. Adding these features, MOST Technology turns out to be resilient and future-proof.
Multi-channel Approach
MOST is a multi-channel network that allows the parallel usage of all services for control data, streaming data and packet data through one network (figure 1). These services are easily synchronized, if necessary, in a highly deterministic way. Based on synchronous MOST frames, the transmission of both native streaming data and packet-oriented data, for example packetized elementary streams, is supported. The third generation of the MOST Specification [1], [2] introduces MOST with 150 Mbit/s. It is supported for both Plastic Optical Fiber (POF) and Coax. MOST150 enables IP data communication, thus providing an automotive-ready Ethernet channel according to IEEE 802.3 with freely configurable bandwidth from 0 to nearly 150 Mbit/s. MOST is open to a broad variety of IP protocol based applications, including seamless integration of wireless mobile devices or car-to-car and car-to-infrastructure communication.
High Streaming Bandwidth
MOST is designed as a synchronous network system solution with high bandwidth, at nearly no overhead for administrative communication for transport of various streaming data. The management of synchronous and isochronous streaming connections allows for an appropriate allocation of resources and thus provides access to quality of service (QoS) communication. Concerning the isochronous channel, QoS IP communication is provided as well.
Hard Real-time and Low Latency Requirements
MOST meets hard real-time and low latency requirements. The MOST system concept is based on inherent synchronicity at the physical layer level. Severe jitter restrictions are held in an automotive environment temperature range from -40°C to 95°C (or even 105°C). Clear distinction between transfer jitter (relevant on the network system level) and alignment jitter (only relevant on the single link level) leads to a robust system design. The specification limits are testable and can be checked during a type approval through compliance verification.
Functional System Model and Safety Aspects
The MOST Framework, with its function block concept, comprises a clear application programming interface which allows simple access to the applications. It is able to standardize interfaces between both infotainment applications and applications of other domains, such as sensor interfaces and camera interfaces. Due to the functional system model, it does not matter whether the communication partner is sitting in the same control unit or connected across the network. MOST150 Technology has already been investigated with respect to safety requirements by corresponding studies in cooperation with the German TÜV [3]. With the help of a safety layer concept on top of the application layer, MOST150 enables fail-safe applications up to SIL level 3 according to IEC 61508 and ASIL D according to ISO 26262 [4]. Moreover, the network can even be mixed with “normal” network nodes without a safety layer.
Robustness and Maturity
Today, MOST Technology has been proven as robust in numerous car models on the road. The latest generation of MOST Specification incorporates the lessons learned. For the third generation of MOST, reference implementations have been realized and several OEMs have had a successful SOP for cars with MOST150 since 2012. MOST stands for a cost efficient system solution approach.
- The inherent synchronicity at the network level lowers the requirements at the component level and turns out as resource saving (e.g. regarding interrupts of the host controller).
- The streaming nature of MOST supports continuously flowing streams of video data with no need for packetization and buffering.
- The TDMA mechanism leads to determinism and ultra-low latency.
- Highest quality of service is provided.
- Standardization of MOST provides reuse of the function blocks, which are a set of standardized commands that allow for synchronized message and event flow.
- MOST provides an IP (intellectual property) pool with royalty-free cross-licensing among the members of the MOST Cooperation. It allows for a straightforward easy grant of license which is based on compliance testing.
- An established compliance verification program with accredited MOST Compliance Test Houses according to ISO 17025 [5] improves the quality of MOST products and leads to simplification of system integration due to pre-tested components.
New Data Types and FCat Exchange Format
The coming MOST Specification 3.1 [6] extends of the existing application framework with new data types [7]. The table lists the available data types and distinguishes between those available in MOST Specification Rev. 3.0 and those that are currently being modified and added with the new MOST Specification Rev. 3.1. Worth mentioning are the new array and record structure, with its nested structure. In many cases, the new data types simplify the modeling of the infotainment system. In addition, the MOST XML language has been overhauled and a new xml schema based exchange format has been created. It allows function and data element sharing and opens up the integration into modern UML based design. The MOST Editor has been updated accordingly and is available to the members of the MOST Cooperation.
Table: Basic MOST data types
MOST150 Design Enables Streaming Bandwidth Increase
One of the new features is a multiport network interface controller that is able to allocate the true, full bandwidth of up to 150 Mbit/s in up to eight branches, thus enabling a streaming bandwidth of up to 1.2 Gbit/s to a central unit. The different branches can be built with any topology, including star, ring, tree, or daisy-chain. They can be hot-plugged or disconnected without influencing the flow of streaming data in the rest of the system. This flexibility can be used for applications such as a surround view camera system of up to eight cameras in a driver assist system (ADAS) network.
Figure 2 shows a MOST150 network based multi-camera system that transmits high definition video streams. The surround view cameras are connected to a central node in a star topology over coaxial cable. The MOST multi-channel network approach, with its inherent synchronicity due to the TDMA mechanism, is perfectly adapted for ADAS since it assures real-time determinism and ultra-low video latency at less than 10 milliseconds. Sending a video stream from the camera to the renderer means that a significant amount of video data is streamed for a prolonged period of time. The continuously flowing streams of data are not interrupted or delayed. The MOST Technology provides the transport of data streams with guaranteed bandwidth and ultra-low latency. It requires neither additional communication processors, nor addressing overhead, nor the bandwidth-wasting process of breaking up the data into packets that then need to be examined every time they go through a device along the route.
Remote Control Feature
The Remote Control Feature is another new feature that is being added to the MOST specification. It allows the reduction of the software stack that typically demands the use of microcontrollers and memory in peripheral nodes such as displays and cameras. For example, the Remote Control Feature supports a control port that implements an I2C bus master. The I2C bus master manages reads and writes to the imager sensor and other on-board slave devices, if any. The I2C reads and writes are remotely handled through the MOST control channel. Also, GPIOs are remotely handled through the MOST control channel. These can be used as reset pin, for example. GPIO events are automatically reported over the MOST network. Existing processing power in the main ECU is used to run the controlling software for all remote controlled nodes. Centralizing all controlling software in the top view ECU simplifies the development process considerably as only one software instance needs to be developed and deployed. This kind of device architecture helps to optimize system partitioning, board space and even power dissipation in the remote device. The Remote Control Feature can also be used for other applications, e.g. “slim” displays as shown in figure 3. Due to it, a memory and an additional microcontroller are not required to run the display.
Fig. 3: MOST "Slim Displays"
Conclusion
This contribution gives an overview about the advantages of MOST150 and the potential of the new features of MOST Specification Rev. 3.1 The multi-channel network approach allows transmission of control messages, video data streams, and packet data in parallel over the same link. It is easy to use the synchronous MOST frames for transmission of packet-oriented data. MOST150 provides an automotive-ready Ethernet channel according to IEEE 802.3 with freely configurable bandwidth from 0 to nearly 150 Mbit/s.
The flexible topology supports both star and ring topology as well as a mixture of it. The multiport concept allows for partial networking, dynamic topologies and also enables redundancy concepts. The streaming nature of MOST Technology based on a TDMA mechanism supports real-time streaming with ultra-low latency and the highest quality of service. Up to 150 Mbit/s can be allocated for each branch, allowing the routing of up to 1.2 Gbit/s of data into the central microprocessor of an ECU in the case of an eight multiport star architecture. Both Plastic Optical Fiber (POF) and automotive proven coaxial cables and connectors can be used. Deployed in over 170 car models on the road, MOST technology provides a robust and mature choice and turns out to be resilient and future-proof.
Literature:
[1] MOST Specification Rev. 3.0 E2. MOST Cooperation, 2010.
[2] Grzemba, A. (Ed.): MOST – The Automotive Multimedia Network – From MOST25 to MOST150. Franzis Verlag, Poing, 2011, ISBN 978-3-645-65061-8.
[3] Lisner, J.; Specht, J.: Definitely Safe. Elektronik Automotive. Special Edition March 2010, p. 32-34.
[4] ISO 26262-6:2011 Road vehicles – Functional safety – Part 6: Product development at the software level.
[5] ISO 17025:2005 General requirements for the competence of testing and calibration laboratories.
[6] MOST Specification Rev. 3.1, Pre-Release. MOST Cooperation, 2015.
[7] Machelett, R: New Data Types and the MOST Function Catalog. Special Edition March 2014, p. 17-21.
About the Author:
Dr.-Ing. Wolfgang Bott is the Technical Coordinator of the MOST Cooperation. He also acts as the MOST Compliance Administrator.
All illustration Copyright MOST Cooperation
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