FreeRTOS critical section causes hard fault

I have a custom board running code (RA6M5/FSP4.5.0/FreeRTOS) which can occasionally generate a hard-fault.

The hard-fault is related to memory access performed inside a critical section. When the system operates solely using taskENTER_CRITICAL() or taskENTER_CRITICAL_FROM_ISR() everything works fine. But mixing the two will eventually cause a hard fault.

The debugger when the hard fault occurs makes the call stack look nonsensical. Its hard to get insight once you are in the hard fault handler.

Investigating taskENTER_CRITICAL I saw this on line 198:

```NOTE: This may alter the stack (depending on the portable implementation)
so must be used with care!```

This lead me to assume this was the case and try to use methods that might fix the issue. In particular I added calls to __DSB() at the beginning of each critical section. These seem to work but only when I run the program using the debugger.

I'm open to trying different primitive instead of a critical section. Inside that critical section is access to a simple circular buffer.

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  • What kind of hard fault do you get ?

    I broke out the handlers below and the HardFault_Handler was the one being called.

    from startup.c:

    void NMI_Handler(void); // NMI has many sources and is handled by BSP

    void HardFault_Handler(void) WEAK_REF_ATTRIBUTE;

    void MemManage_Handler(void) WEAK_REF_ATTRIBUTE;

    void BusFault_Handler(void) WEAK_REF_ATTRIBUTE;

    void UsageFault_Handler(void) WEAK_REF_ATTRIBUTE;

    void SecureFault_Handler(void) WEAK_REF_ATTRIBUTE;

    void SVC_Handler(void) WEAK_REF_ATTRIBUTE;

    void DebugMon_Handler(void) WEAK_REF_ATTRIBUTE;

    void PendSV_Handler(void) WEAK_REF_ATTRIBUTE;

    void SysTick_Handler(void) WEAK_REF_ATTRIBUTE;

    Also how do you mix taskENTER_CRITICAL and taskENTER_CRITICAL_FROM_ISR ?

    I would say that the shared resources protected by these calls are both types.

    A timer interrupt is producer of data, a timer interrupt is consumer of data, and sporadically a task is a producer.