9. Software Architecture

The following section describes the diagnostics and safety focused BMS software architecture as depicted in Fig. 9.1

Software architecture

Fig. 9.1 foxBMS 2 - Software architecture

A hardware abstraction layer (HAL) provides various interfaces to directly access the hardware and its peripherals. This enables encapsulation of the actual BMS software implementation from the hardware and eases porting the foxBMS 2 software to different microcontrollers.

The open-source real-time operating system FreeRTOS is the centerpiece of the software architecture. Its reliable kernel is ideally suited to ensure the compliance of all soft and hard real-time requirements of a battery-management system. Furthermore, it provides a migration path to SafeRTOS, which includes certifications for the medical, automotive and industrial sector, if a certification is required by the application.

Three scheduled tasks with a period of 1ms, 10ms and 100ms are configured to execute the various deterministic finite-state machines that describe the behavior of the BMS. Time-sensitive software modules (e.g. diagnostics, measurement, CAN reception, …) are called within the 1ms task, whereas less time critical modules (e.g., CAN transmission, interlock, BMS, …) are located inside the 10ms task. Software modules that are temporally uncritical (e.g., state estimation, balancing, …) are handled by the 100ms task. An additional asynchronous task is used to implement a data-exchange layer between the different concurrent tasks and processes. This data-exchange layer runs with the highest priority of all tasks and is interfaced using queues either to send or to receive data. These FreeRTOS queues are formally verified for memory safety, thread safety and functional correctness.

The foxBMS software itself is grouped into three different layers:

  • A dedicated driver layer using the HAL interface provides different communication interfaces (CAN, UART, SPI, …) monitor BMS peripherals, their status (e.g. supply voltages, transceivers, …) as well ass the BMS slaves.

  • Diagnostic functions and error handling, system monitoring (for hard- and software) and interfaces to the data-exchange layer are the most important tasks of the BMS Engine.

  • The actual BMS implementation including the monitoring of the safety parameters (e.g. safe-operating area, contactor state, communication errors, …), state estimation functionalities (state-of-charge, state-of- health, state-of-energy) and the vehicle specific BMS application is done within the application layer.