During development and production of automotive ECUs their interfaces are subject to extremely diverse requirements. Standardization of interfaces promises to simplify the tasks of development engineers in acquiring measurement data and calibrating parameters. The XCP calibration protocol, besides achieving independence of the transport layer, offers other advantages as well.
During the ECU application process, the three basic functions of measuring, calibrating and flash programming are of crucial importance. For example, in developing a driving dynamics control system, various parameters such as wheel speed and brake pressure serve as input variables for the control algorithms used in the ECU.
These algorithms that influence vehicle behavior are created and optimized over the course of the development process. Since an ECU might in some cases be utilized in several vehicle models of a particular OEM, identical input variables and algorithms may need to satisfy different requirements for later driving behavior. Therefore, algorithm parameters are not calibrated until the ECU is configured for specific vehicle variants. For example, in controlling the brakes although the same algorithms are used the parameter values will differ due to differences in the physical properties of each vehicle type, e.g. weight distribution.
To evaluate the effects of parameter calibration, the application engineer taps into the relevant parameters at sensors and actuators using conventional measurement technology. Nevertheless, such methods do not give access to internal ECU variables, e.g. to the intermediate results of a computational function. The developer can only obtain such data via a special measurement and calibration interface, the CAN Calibration Protocol (CCP) or the Universal Measurement and Calibration Protocol (XCP).
The ASAM MCD Interfaces Model
The Association for the Standardization of Automation and Measuring Systems (ASAM), an international organization founded in 1991 by European Automotive OEMs and suppliers, has developed and promoted a model that enables the development of standardized and therefore manufacturer-independent interfaces.
Figure 1: ASAM MCD interfaces model
Figure 1 shows the ASAM interfaces model comprised of the following components:
• ASAM MCD 1 " CCP/XCP:
CCP/XCP provides all necessary services for acquiring internal run-time variables of the ECU (measurement variables) and for calibrating control algorithms by modifying parameters.
• ASAM MCD 2MC " Standardized ECU description file:
The ASAM MCD 2MC interface (previously ASAP2/A2L) defines a file format for describing ECUs. This file contains all information needed for access to the ECU by the measurement and calibration system (MC system), e.g. CANape[visheh1] from Vector. Specifically the ECU description file contains information on the memory address, data type, data format and conversion of internal ECU parameters to physical parameters.
• ASAM MCD 3MC " Standardized interface for an automation system:
The MC system makes its functionality available to other applications via the standard ASAM MCD 3MC interface. This interface acts as a server for accessing the connected ECU. The interface's primary functionality involves acquiring measurement data and calibrating parameters.
The CAN Calibration Protocol (CCP) was the first protocol to be defined for communication between the ECU and the measurement and calibration system. The CCP interface provides all functions needed for real-time acquisition of the ECU's internal run-time variables and measurement signals and for calibration of ECU parameters. However, CCP usage is limited to the CAN bus.
Data throughput requirements vary significantly over the various development phases that an ECU passes through. Therefore vehicle OEMs and suppliers also utilize non-CCP interfaces for their measurement, calibration, diagnostic and flash-programming tasks.