Hvordan debugger man “HardFault_Handler” med FreeRtos og ARM Cortex-M

Når man arbejder med FreeRtos sker det (ret ofte), at man får et system crash, der ender i HardFault_Handler handleren, og så vil man jo gerne vide, hvad der gik galt.

Dette kan bedst gøres ved at undersøge indholdet af Cortex -M registrene.

Det kan gøres ved, at indføre nedenstående kode i HardFault_Handler  funktionen.

Det mest interessante register er PC (Program Counter) registeret, som viser hvor problemet opstod.

void prvGetRegistersFromStack( uint32_t *pulFaultStackAddress )
{
/* These are volatile to try and prevent the compiler/linker optimising them
away as the variables never actually get used.  If the debugger won't show the
values of the variables, make them global my moving their declaration outside
of this function. */
volatile uint32_t r0;
volatile uint32_t r1;
volatile uint32_t r2;
volatile uint32_t r3;
volatile uint32_t r12;
volatile uint32_t lr; /* Link register. */
volatile uint32_t pc; /* Program counter. */
volatile uint32_t psr;/* Program status register. */

    r0 = pulFaultStackAddress[ 0 ];
    r1 = pulFaultStackAddress[ 1 ];
    r2 = pulFaultStackAddress[ 2 ];
    r3 = pulFaultStackAddress[ 3 ];

    r12 = pulFaultStackAddress[ 4 ];
    lr = pulFaultStackAddress[ 5 ];
    pc = pulFaultStackAddress[ 6 ];
    psr = pulFaultStackAddress[ 7 ];

    /* When the following line is hit, the variables contain the register values. */
    for( ;; );
}

static void HardFault_Handler(void)
{
    __asm volatile
    (
        " tst lr, #4                                                \n"
        " ite eq                                                    \n"
        " mrseq r0, msp                                             \n"
        " mrsne r0, psp                                             \n"
        " ldr r1, [r0, #24]                                         \n"
        " ldr r2, handler2_address_const                            \n"
        " bx r2                                                     \n"
        " handler2_address_const: .word prvGetRegistersFromStack    \n"
    );
}

 

/Flemming Jahn

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