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SPI Interface Customization in Airbag ECU Testing

Hardware-in-the-Loop Test Relies on ADwin System

CAS DataLoggers recently provided the data acquisition solution to an automotive manufacturer in a real-time Hardware-in-the-Loop (HIL or HWIL) automotive test simulation application for their airbag electronic control units (ECUs). Airbag test is a common HIL application in automotive development to ensure that components function properly and are up to specification. Here a particular airbag ECU chip is the H (hardware) under test in the loop. This chip governs airbag deployment, so only after rigorous testing can it be approved for production and use in actual driving conditions.

In HIL test applications, individual components are the DUT (device under test) while the rest of the automobile is absent but simulated mathematically. The DUT interacts with all simulated subsystems during the test. In this case, the airbag ECU chip under test uses a Serial Peripheral Interface (SPI) to communicate. However SPI is not an all-inclusive standard but is handled differently for each individual application. The lead test engineer wanted a control system to customize the required SPI slave interface in order to ensure that the chip is performing to specification (i.e. able to handle actual road conditions). His test engineers also needed a system which could quickly compile test programs for faster application development—they were tired of relying on systems that took two to three hours to finish!

ADwin Architecture:

The lead test engineer contacted the North American ADwin distributor CAS DataLoggers who supplied an ADwin-Pro-II Data Acquisition and Control System. This system is installed within a control cabinet in the automotive test lab, fulfilling the need for connection to the airbag ECU, for current stimulation to accelerometer sensors, and for SPI interface simulation.

ADwin is widely used in automotive test applications and for test stand control. Using the ADwin system, users can acquire the analog/digital signals and I/Os of the ECU under test, while the timing of all signals and messages can be evaluated online at microsecond accuracy with an I/O response time of 1 microsecond. The system’s sample rate is on an order of 100kHz aggregate, to 1.25 MHz per channel. In this way users can accurately and thoroughly test the ECU. The ADwin is also equipped with a local processor with its own real-time operating system running independently from a Windows CPU so that it will continue to run even if the PC crashes.

SPI Customization:

Since SPI sensors don’t share a common SPI standard, simulation must be handled individually. The customer provided CAS DataLoggers with the data sheet for their particular ECU chip. ADwin’s German manufacturer, Jager-ADwin, used this information to customize an ADwin PRO-II system to generate the SPI slave interface for this application. Through ‘Master Out Slave In’ or MOSI, the ECU chip provides the clock and sends commands to the ADwin which then sends the chip a given acceleration value in 10-bit resolution as the desired answer. The ADwin includes all signals on the SPI interface into the ECU test run.

Here the ECU’s onboard high-g acceleration sensors are surface-mounted on the airbag ECU itself to detect a crash event. Each of these micromechanical sensors are connected to the ADwin, one per analog channel. These single-channel sensors are based on digital 16-bit SPI interface. During real-world use, these sensors deploy the airbag by detecting the deceleration of the automobile during a crash event.

Current Stimulation: 

The ADwin-PRO-II’s outputs stimulates the DUT using analog signals and controls the acceleration value each sensor receives, which the PRO-II then measures and records. Acceleration is relatively easy to simulate using an ADwin system, which greatly simplifies this HWIL test application.

The PRO-II control system produces the acceleration signal via current stimulation to the ECU’s inputs with a current of varying amount. This acceleration value determines whether the airbag deploys or not. In this case the particular airbag has a 2-ohm resistance. Every current administered below 500mA is considered to be a test current, used to test varying aspects of performance, for example if the airbag is mounted properly, etc. In contrast, current above 5 amps is termed the ‘explosion current’ and this verifies if the airbag itself is deploying properly, as it should in a real crash event.

Additionally, the ADwin simultaneously monitors the tested ECU’s outputs and evaluates them online via Ethernet in order to verify whether the stimulation and the ECU’s response correspond to the chip specifications. ADwin also generates a CANbus simulation, simulating that the car’s missing CANbus network is present so that the ECU doesn’t go to sleep.

Fast Compiling:

Users have discovered that the ADwin’s fast compiling time greatly speeds application development. Before using ADwin, test engineers had to wait hours after programming their application—now with ADwin compiling is finished in seconds!

Versatile Communications:

ADwin offers test applications a variety of communications options including connection to a PC via Ethernet (USB optional) to begin the test run and exchange results. As mentioned ADwin can also interface with CANbus. If users require standalone operation, an available boot option allows for fully-functional operation independent of a PC or external computer.

Test Visualization Software:

The ADwin software directly connects with Windows without risk of OS crashes and lockups. This software can be used under Windows and LINUX or as a stand-alone data acquisition system. Users are free to develop their test stand application with a full set of available drivers (VB, VC/C++, LabVIEW, TestPoint and more) enabling full integration with other applications and programming languages including MATLAB.

ADwin systems are also bundled with Kalliste’ development software for test data acquisition applications. Designed specifically for test engineers, Kalliste’ allows users to program using only plain English sentences, and supplies users’ needs for data acquisition, test bench supervision, after-test data analysis and test reports.

Hardware-in-the-Loop Test Benefits:

The test team’s airbag ECU test development significantly benefitted from the ADwin data acquisition and control system. Here a single test system–the ADwin-Pro-II—simulates the ECU chip’s specification by customizing the SPI interface, stimulating the ECU test unit, and measuring the acceleration response. Whether for hardware-in-the-loop tests or other test stand applications, ADwin offers high speed and flexible communications. Before installation, the lead engineer used to return from lunch to find that programs had not yet been compiled or had errors, but with the PRO-II system, compiling is finished in moments.

This all leads to a thoroughly-tested component which in turn leads to improved airbag safety and a more reliable automobile.