Automotive HMI: More than just a machine interface

Key requirements influencing the development of the second generation of this processor family were modularization and the implementation of flexible system architectures. To this end, internal components were defined to support the goal of implementing cost-effective embedded applications.

By its very nature, display instrumentation is very diverse. Within the vehicle, instrumentation often offers us a combination of scalable displays, conventional dial instrumentation, LEDs and tell-tales. As with its predecessors, ‘Indigo2’ is optimized for these applications as a standalone GPU (graphics processing unit) that is controlled by a host controller over an APIX interface. Version 2 of the APIX standard offers a usable bandwidth of 3 Gb/s, with which video and control data can be transmitted between host controller and GPU – even over large distances.

Equipped with the first APIX generation, today’s MB88F332 ‘Indigo’ is managing the displays for a wide range of vehicle applications. In addition to high bandwidth, the APIX2 video and sideband links offer further innovations. This enables the uncompressed, simultaneous and real-time transmission of two completely different video content streams – such as video for the instrument cluster and for the main display of a vehicle application. In addition, the video link also offers enough bandwidth for up to eight digital audio channels. Copyright protection is also taken into account. Since this kind of data is also carried in the vehicle for e.g. passenger entertainment, unauthorized access to the data must also be prevented. For this reason, APIX2 has been enhanced to include logic that permits (de)encryption of video data using HDCP (High Density Content Protection).

A crucial part is also played by the sideband link, which is used to transmit full-duplex control data. Control data consists of the commands or parameters exchanged between the host controller and the ‘Indigo2’ peripheral circuitry. The protocol offered by the integrated ‘A-shell’ – also an integral part of the APIX2 block – ensures the orderly addressing of the data packets. For the developer, the sideband offers a major advantage, since it grants the control unit access to the display unit. Here, the display is the central component and developer interface. Depending on the application, this may also feature other display elements, such as dial instrumentation, LEDs or tell-tales, which can be used by the control unit via ‘Indigo2’. In the opposite direction, the APIX2 sideband sends the control unit the coordinates of user interaction with the touch display or data from brightness or temperature sensors. The control unit then evaluates this data and executes the appropriate actions. The interfaces round off the connection to the display and sensors. On the display output side, a range of features have been implemented in order to design greater technical flexibility into the controller and reduce system costs.