[Success Story]
Can BMW's iDrive Pass Its Road Test Now?
After a catastrophic debut and a major makeover, BMW's iDrive infotainment system is gaining acceptance with critics, competitors, and customers.
QUARTET OF MCUs At the heart of the second-generation (5 and 6 Series) iDrive are four microcontrollers (MCUs) located in the head unit: a main processor for navigation and MMI (multimedia interface); a companion chip for graphics; an MCU and digital signal processor (DSP) for sound management; and an interface controller that functions as a gateway and provides security.
Renasas Technology (formerly Hitachi) supplies the main processor, a 430-MIPS at 240-MHz SH775x, and the companion chip, an HD64404 Car Information System (Amanda) incorporating a 2D graphics engine, video input, and communication and networking peripherals. SH-4 Product manager Matthias Wenzel notes that Renesas recently introduced the SH7770 system-on-a-chip, which combines an SH-4A core with both 2D and 3D graphics engines in addition to GPS2 baseband processing and a plethora of peripherals.
Immersion's Levin explains that when a driver pushes or slides the controller to a section of the display screen to select a function, the screen changes and a set of commands is downloaded from the Renesas processor via a controller-area-network (CAN) bus to the processor in the control unit (a 16-bit Freelink MCU).
The commands tell the controller what haptic profile to play. "Haptic profiles contain instructions for detents, hard stops, 'hills,' and other touch-sensitive responses," according to Levin. "Speaker balance requires a detent, for example, whereas a hill is used as a permeable barrier to separate one section of the screen from another. In the case of audio, drivers can select from a list of available sources on the left side of the screen, such as AM, FM, or CD. Then they 'pop' over to the right side of the screen by turning the knob in that direction and select stations or tracks, with the touch appropriately different for each."
As the controller moves or a button is pushed, the controller feeds its position change to the system processor, an event change is registered, and new haptic commands are transmitted and initiated. "The controller doesn't know what it's controlling but knows what 'feel' is appropriate on a screen-by-screen basis," says Levin.
A communications processor interfaces with the vehicle's CAN, LIN (Local Interconnect Network), and MOST (Media Oriented System Transport) buses. "In a system like the iDrive, there are more than 5000 MOST function calls that can be combined in various ways to meet application requirements," says Oasis Silicon Systems' Christian Thiel.
"When the car is activated, all devices are awakened. They boot their hardware and operating systems and are then ready for communication," explains Thiel. "Usually, the system configuration is first checked by a central network master. If it is okay and all device addresses in the system are unique, the network master gives the start command for communication, and the devices begin to initialize their applications."
He continues, "The HMI device loads and displays status information—for example, the current CD track. Audio and video streaming are initialized if required. As the driver begins to use the system, commands are transmitted and status information is exchanged. When the car is parked, a shutdown sequence is initiated by the Network Master and the system goes to sleep."
Low power is as much a consideration in a vehicle as it is in a portable device, according to Brian Fortman, telematics marketing manager at Texas Instruments. "The electronics content of cars is growing. There are a lot of MCUs, and a lot of nodes on a MOST network, and that means there are a lot of potential places to drain the battery if they're kept active when the engine is not running. Automakers' requirements for power drain in standby mode is often less than one milliamp, which puts heavy constraints on DSP designs."
To meet those requirements, vendors are integrating DSPs and other processors on a single piece of silicon, much like Renesas did in combining its SH-4 core and companion processor on one chip. Such integrated designs are likely to find their way into future iDrive generations. Among Würtenberger's other plans for iDrive is to implement the high-bandwidth (10 Mbits/s versus 1 Mbit/s for CAN), deterministic automotive communications protocol called FlexRay. BMW is a founding member of the FlexRay Consortium (see "Driving A Faster Bus," for more information).
"The iDrive was a very brave, very revolutionary step in how to connect an operator with a vehicle," says Immersion's DiNucci. "They missed putting a $75,000 7 Series car in the hands of an automotive journalist without having a succinct way to jumpstart their knowledge."
"[The] iDrive is important not just for what BMW did in offering such a new interface, but for the other automakers that subsequently introduced or are developing something similar," notes Rob Barnicoat, director of Business Development at Harman Becker Automotive Systems, a developer of MMI (multimedia interface) software. Audi's A8 has an interface similar to iDrive, as will a new line of Mercedes S-class vehicles planned for introduction next year.
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