The basics of automotive cluster device architectures and applications, part I
- Types of cluster devices
- Autosar application component
- Graphics application component
- Cluster security
- Device memory requirement
- Low power mode cluster architecture
Cluster Device Types
There are three basic cluster device platforms, including:
Cluster Graphics Platform
Car manufacturers and tier-1 suppliers are facing an increasing need for content to be displayed to the driver requiring instrument cluster solutions that can be dynamically reconfigured to display content based on context and driver preferences while presenting required information to ensure safe driving. Cluster graphics Platform is mainly used to fulfill the requirement. This device mainly consists of Graphics processor with 2D/3D accelerator, huge on-chip graphics RAM for high bandwidth graphics data access, high-speed external memory interface like SDR,DDR or Nand Flash Controller, display controller to display graphics information through TFT,LCD display. In addition, the set of integrated peripherals such as CAN, MOST MLB, LVDS, Ethernet and USB allow a direct connection to the rest of the car network. The device is generally used for high end cluster application by OEMs.
Cluster Controller Platform
This is the cluster MCU device that mainly handles the Cluster AUTOSAR stacks functionality. This device contains a stepper motor controller and driver for gauge driving, sound generation module, PWM channels for sound and cluster LED control, various analog sensors and communication peripherals, HMI to communicate with driver, other body devices and gateway devices or other subsystem. The device can also have segmented LCD or even dot matrix LCD displays as an alternative display solution for low end cluster application. For high/mid range applications, most of the real time data and status captured by the device is communicated to cluster graphics device through fast SPI or EBI interface.
Combined Cluster Platform
The graphics controller and real time application controller (Cluster MCU) is combined in this platform to make single chip solution for both Graphics and Autosar application. This device keeps a balance between graphics performance and real time performance hence used by OEMs when optimum solutions are required. Some renowned semiconductor companies offer wide range of combined cluster platform microcontrollers with multi core based solutions to support from basic to premium line instrument cluster applications.
1. AUTOSAR Application Components
Core: The core is part of real-time application domain of the device. It is mainly used to run AUTOSAR applications such as basic a communication driver, PWM driver, handling and servicing of various peripherals etc. The high bandwidth motor control application driver can also be controlled through this core. The device can also have a dedicated core for motor control applications, which helps to share the bandwidth of the real time processor.
Stepper Motor Control/Driver: In cluster application a stepper motor driver is mainly used to control gauges. Real-time information of vehicle speed, fuel level, tachometer, temperature etc., is communicated to cluster devices through a gateway device. The core then processes that information and updates the motor control driver to control the stepper motor. Two motor control channels are mainly used to drive a single stepper motor.
PWM: PWM outputs are used to control the backlighting of LCD displays, gauge backlighting etc. The LED intensity of dashboard, odometer, etc., are controlled by PWM output. For low-end applications where few LED tell-tales are required, it is controlled by microcontroller PWM output. However in mid-range or high-range applications where more LEDs need to drive the system, there is typically a dedicated LED driver.
ADC and Alarm Comparator: These analog components are mainly used to monitor the current, voltages of various power supplies. They are also used to measure the current flow through Telltale LEDs to check that everything is working fine. Measuring the battery level, ignition level, air temperature and coolant are common ADC functions performed by either a cluster or body device. When performed by a body device, it is communicated to a cluster by using a LIN or CAN connector.
Sound Generation Module: The device can have sound generation module with I2S protocol support, mainly to produce a buzzer sound in a cluster to indicate the occurrence of some unwanted event. For example, a driver seat belt warning detected by a body-device sensor is communicated to a cluster. The sound generation module inside the cluster device will create a buzzing sound to alert the driver of the event. Similarly door lock/unlock and other common events can be communicated through a sound generation module. It can also be used to play MP3 audio data with the help of a CPU that converts MP3 into PCM data for the I2S interface.