Standardized video interface for in-car applications
Since driver assistance systems have been providing drivers with important safety functions, cameras have also been used as functional elements to provide all-round vision. Originally still integrated in ECUs, highly equipped vehicles now have between six and twelve multi-function cameras in the form of independent units. A high-performance digital interface is required to connect the cameras to the appropriate ECUs.
Standards for this video communication interface were developed and published in the ISO 17215 (Parts 1–4) series of standards. This series of standards defines both the requirements for the communication protocol and those for the physical interface.
The illustration shows the allocation of the individual parts of the standards in terms of content, based on the ISO/OSI reference model for communication between cameras and control units.
To enable a camera to be operated in the vehicle and evaluate the image information, the communication protocol must support the appropriate functions on the application interface. Essentially, these are, on the one hand, function for the controller, for calibration and error handling for the camera, and on the other, functions for the periodic transfer of image data. The “Scalable Service-oriented Middleware over IP,” or “SOME/IP” for short, has been specially developed for the automotive industry to sequence these functions and data structures.
One of the features of SOME/IP is that data types and structures that are defined in the application layer can be transferred without complex recalculations. The “service orientation” of this middleware makes the following transmission methods possible: request/response, fire and forget), event, field and event group.
The illustration below visualizes the messages of the corresponding transmission methods between sender (client) and receiver (server).
The TCP/IP protocols familiar from PC networking and the Internet are used to transfer between protocol layers 4 to 1 (see Figure 1). Ethernet has been specified in the ISO 17215 series of standards for the physical transfer. Ethernet provides a more bandwidth and faster data transfer compared to other vehicle bus systems such as CAN, MOST and FlexRay. Ethernet in the vehicle is based on general standards, which have been specially adapted to the requirements and conditions in the vehicle. The “SOME/IP” middleware has been specially developed and adapted for the use of Ethernet in the vehicle to enable the bus properties familiar from CAN and FlexRay to be reproduced better.