3. Software Structure Overview

3.1. Startup

The startup code begins in the function _c_int00() in app/main/fstartup.c. After initialization of the main microcontroller registers, memory, system clock and interrupts, the C function main() is called. In general/main.c, interrupts are enabled and the initializations of the microcontroller unit, peripherals and software modules are done (e.g., hardware modules like SPI and DMA). The OS is then started. The steps are indicated by the global variable os_boot. At the end of the main function, the operating system resources (tasks, queues) are configured in OS_InitializeOperatingSystem() (src/app/task/os/os.c) and the scheduler is started. All configured tasks (FreeRTOS threads) are then started depending on their priority. The successful activation of the tasks is indicated by os_boot = OS_RUNNING.

The OS-scheduler first calls the highest priority task. All other cyclic tasks are blocked in a while-loop until the initialization of this task finishes. At the beginning of the task, FTSK_InitializeUserCodeEngine() is called. In this function, the database is initialized. Once finished, this is indicated by os_boot = OS_ENGINE_RUNNING. The function FTSK_RunUserCodeEngine() is then called, where the diagnostic module and the database are managed.

Once os_boot = OS_ENGINE_RUNNING, the 1ms cyclic task is unblocked. The function FTSK_InitializeUserCodePreCyclicTasks() is called once first. This function is called when the OS and the database are running but before the cyclic tasks run. Once FTSK_InitializeUserCodePreCyclicTasks() has finished, all cyclic tasks are unblocked from there while-loop and run periodically.

3.2. Operating System

A critical section must be entered with the function OS_EnterTaskCritical() and exited with the function OS_ExitTaskCritical().

The operating system configuration can be found in the file FreeRTOSConfig.h. A detailed explanation of the parameters configured in this file is given at https://www.freertos.org/a00110.html. HALCoGen generates the FreeRTOS sources on the fly during the build process. However, foxBMS 2 ships its own FreeRTOS source tree (in src/os/freertos), and therefore the FreeRTOS sources generated by the code generator are not needed and consequently removed. Only the CPU clock frequency configured with HALCoGen is extracted from the generated FreeRTOS sources and written into config_cpu_clock_hz.h, which is included in foxBMS 2’s own FreeRTOSConfig.h.

3.3. Software Architecture

The database runs with the highest priority in the system and provides asynchronous data exchange for the whole system. Fig. 3.2 shows the data exchanges implemented via the database.

Fig. 3.2 Asynchronous data exchange with the foxBMS 2 database

Fig. 3.3 shows the main structure of foxBMS 2.

Fig. 3.3 Main tasks in foxBMS 2

The two key modules used are:

• SYS

• BMS

SYS has a lower priority than the database and a higher priority than BMS. Both modules are implemented as a state machine, with a trigger function that implements the transition between the states. The trigger functions of SYS and BMS are called in FTSK_RunUserCodeCyclic10ms().

SYS controls the operating state of the system. It starts the other state machines (e.g., BMS).

BMS gathers info on the system via the database and takes decisions based on this data. The BMS is driven via CAN. Requests are made via CAN to go either in STANDBY mode (i.e. contactors are open) or in NORMAL mode (i.e. contactors are closed). A safety feature is that these requests must be sent periodically every 100ms. BMS retrieves the state requests received via CAN from the database and analyses them. If the requests are not sent correctly, this means that the controlling unit driving the BMS has a problem and the correctness of the orders sent to the BMS may not be given anymore. As a consequence, in this case BMS makes a call to CONT to open the contactors. Currently, BMS checks the cell voltages, the cell temperatures and the global battery current. If one of these physical quantities violates the safe operating area, BMS makes the corresponding call to CONT to open the contactors. BMS is started via an initial state request made in SYS.

A watchdog instance is needed in case one of the aforementioned tasks hangs. This watchdog is made by the System Monitor module which monitors all important tasks (e.g., Database, SYS, BMS): if any of the monitored tasks hangs, this will be detected.

A last barrier is present in case all the preceding measures fail: the hardware watchdog timer. In case it is not triggered periodically, it resets the system.

3.4. Diagnostic

The DIAG module is designed to report problems on the whole system. The events that trigger the DIAG module have to be defined by the user. The event handler DIAG_Handler(...) has to be called when the event is detected. The way the system reacts to a Diag event is defined via a callback function or by the caller according the return value.

3.5. Data stored in the database

The following data is stored in the database:

• Cell voltages

• Cell temperatures

• SOX (Battery state, contains e.g., State-of-Charge)

• Balancing control

• Balancing feedback

• Current sensor measurements (includes pack voltages at different points)

• Hardware information

• Last state request made to the BMS

• Minimum, maximum and average values for voltages and temperatures

• Measurement from isolation monitor

• Interface to communicate via I2C with extra functionalities on slave (e.g., EEPROM, port expander)

• Result from open-wire check on slaves

• Error state of the BMS (i.e. error flags, set to 0 or 1)

• MSL, maximum safety limits

• RSL, recommended safety limits

• MOL, maximum operating limits

• Calculated values for moving average

• Contactor feedback

• Interlock feedback

• BMS state (e.g., standby, normal, charge, error)

• Current limits calculated for State-of-Function

• Voltages read on GPIOs of the slaves