How to augment your automotive safety applications with the IMU ASM330LHB

Denise SANFILIPPO · ‎2024-05-13

Introduction

This knowledge article explains how you can augment your automotive safety applications, relying on the new automotive IMU ASM330LHB.

The ASM330LHB is a 3-axis digital accelerometer and 3-axis digital gyroscope module that is suited for automotive systems with safety standards up to ASIL B. It is used for redundancy (as two modules) for safety-compliant applications and comes with a dedicated free-of-charge software library called ASILB-LIBRARY.

1. Automotive safety applications augmented by ASM330LHB

The IMU ASM330LHB is an automotive-qualified MEMS inertial-sensing module which addresses functional-safety applications up to ASIL B if it is used in redundancy with the software library ASILB-LIBRARY.

This solution is used to target ASIL B applications that need information about the linear accelerations and angular rates of the vehicle. Use cases can range from in-dash car navigation, precise positioning, V2X (vehicle-to-everything), radar, lidar, and camera stabilization systems or others.

An application example is shown in the picture below, which describes a precise positioning module where IMU sensors are used together with GNSS receiver and antenna protection.

Figure 1: Application example where a precise positioning module based on ASM330LHB is used.

In this scenario, ASM330LHB is the candidate as a 6-axis IMU because of its high-accuracy inertial measurements. In fact, it can improve the precise positioning of the car in context if it is used in redundancy with the software library ASILB-LIBRARY.

2. The ASILB-LIBRARY

The ASIL B software library has been certified independently by TÜV SÜD in accordance with the automotive functional-safety standard ISO26262. Furthermore, it implements software mechanisms focused on data integrity and data accuracy.

The ASILB-LIBRARY is compliant with MISRA C guidelines and it implements robust software safety mechanisms detailed in the safety manual AN5691. The library has a low memory footprint, and it is platform independent. The implementation of write, read, SysTick, and delay functions are delegated to the user via function pointers.

Figure 2: ST offers a solution based on two identical ASM330LHB inertial measurement units (IMU 1 and IMU 2) as well as the ASILB-LIBRARY software library, called "Sensing module" and "Safety Engine", respectively, for applications up to ASIL B.

Interfacing the sensing module composed of two ASM330LHB IMUs involves the following phases:

Configure the sensing module
Check that the sensing module before starting the data acquisition
Acquire and runtime check the data coming from the sensing module

Each library API returns an error code.

An error is uniquely represented by a bit flag
The error code is an unsigned integer number containing the OR-ed bit flags

Figure 3: Design concept of ASM330LHBxx_ASILB_library.

3. Hands-on

Here is a demo based on ASM330LHBxx_ASILB_library in the Unico-GUI for the ASM330LHB, using DIL24 STEVAL-MKI236A connected to the STEVAL-MKI109V3 motherboard.

After launching the Unico-GUI software, choose the STEVAL-MKI236A board with ASM330LHBxx_ASIL_B support, and click on the [Select Device] button. Once the device is selected, the main window appears in a few seconds. The current firmware implementation communicates with the sensor using the SPI communication protocol.

Figure 4: Unico launcher.

Figure 5: Unico main window.

The integration provided consists by the following tools:

Accelerometers plot
Gyroscopes plot
Data visualization

Figure 6: Plot tool.

Figure 7: Data tool.

3.1 Library configuration

The main window exposes the following tabs:

Options
Save

The Options tab allows the user to initialize ab_struct and set selected parameters on the device once the [Initialize library] button is clicked. The mentioned button requests ab_init and ab_chck command execution. All parameters are set in the ab_struct including the read-only “device” parameter, which cannot be edited by the user since it is hardcoded according to the device selected.
Once the [Initialize library] button is clicked, if the ab_init error code is null, the [Start] button is enabled and the sensor data stream can be requested.

Error code box, box 2 in Figure 8, lists:

ab_init error code (Populated after ab_init execution is triggered by the [Initialize library] button)
ab_chck error code (Populated after ab_chck execution is triggered by the [Initialize library] button)
ab_stop error code (Populated after the [Get Tuning Data] button is clicked)

Figure 8: [Options] tab.

Unico button command	ASM330LHBxx_ASILB_library
[Start]	ab_start
[Stop]	ab_stop
[Initialize library]	ab_init + ab_chck

The tuning box exposes tuning parameters retrieved on stop requested by clicking the [Get Tuning Data] button (button 3 in Figure 8). This button cannot be clicked if the [Start] button was never clicked.

The runtime box in the options tab contains steady flag control to set a steady flag parameter on the device while sensors are streaming data. The steady flag should be enabled when the device is in a steady condition, and it enables dedicated checks during the ab_process instructions execution. When the control value is changed, the *ab_stdy command is sent to the library with a value to set.

3.2 Data logging

The save tab allows the user to save a stream of sensor output data including error code on a dedicated log file selected by clicking the [Browse…] button, the user can select data to store. Once the destination file path is selected, the [Start] and [Stop] buttons define the acquisition period.

Figure 9: [Save] tab.

More details are available in the user manual UM3134.

Conclusion

ASM330LHB, used in redundancy (as two modules) and in combination with a dedicated software library, has been evaluated as compatible to be adopted in ASIL B automotive applications. This solution is described in detail in the safety manual AN5691.