arm cortex m0 nf51822 c programing hard fault, really puzzled

Question

I was trying to transform a char type buffer into a struct defined by me in order to analyze the buffer by TLV. But i jumped into hard fault again and again.

codes are these: a little bit long.

#define BigtoLittle32(A)   ((( (uint32_t)(A) & 0xff000000) >> 24) | \
                                   (( (uint32_t)(A) & 0x00ff0000) >> 8)   | \
                                   (( (uint32_t)(A) & 0x0000ff00) << 8)   | \
                                   (( (uint32_t)(A) & 0x000000ff) << 24))

enum {
    DISH = 0
} CB_DISH_TLV_TYPES;

typedef struct cb_tlv_node_s
{
    uint32_t type;
    uint32_t length;
    char value[0];
} cb_tlv_node_t;


typedef struct cb_ble_buffer_s {
    uint16_t total_length;
    uint16_t current_length;
    int8_t current_data_id;
    int8_t expect_package_id;
    char buffer[500];
} cb_ble_buffer_t;

static cb_ble_buffer_t                  current_buffer;

cb_tlv_node_t *
cb_tlv_read(char *buffer)
{
    uint32_t a,b,c,d;
    cb_tlv_node_t * tlv_p;
    tlv_p =  (cb_tlv_node_t *)buffer;
/*    tlv_p->length = BigtoLittle32(tlv_p->length);*/  //this code also cause hard fault
/*    tlv_p->type = BigtoLittle32(tlv_p->type);*/  //didn't test this one ,but high risk causing hard fault

    return tlv_p;
}

//ble packages are reorgnized and call this function. it excutes in the ble recieve interupt
int
cb_dish_data_processer(char * data, int length)
{
    assert(data != NULL);
    assert(length > 0);


    cb_tlv_node_t *tlv_p = cb_tlv_read(data);

    //test
    int a = sizeof(CB_DISH_TLV_TYPES);

    //if ((char)tlv_p->type != DISH) { //this code is fine and steady
    if (tlv_p->type != DISH) {         //this leads to hard fault
        return CB_PC_CODE_UNRECOGNIZE;
    }

    cb_dish_tlv_read(tlv_p->value, tlv_p->length);
    return CB_PC_CODE_PROCESSED;
}

Fist I am sure that pointers are not lost ,so there should not be any kind if illegal address been used; Second I assume my process is too long to be in an interrupt so I moved my codes out side and excite in the main loop, but still useless;

So I am stucked here, I can't find any reason causing this. if you need more info ,leave a message, I will be waiting online. ps:the hardware board is Nordic nf51822 with 8kB RAM, 256kB flash ROM

BTW:Is it true that calloc and other alloc functions are forbidden in this kind of boards? because when I try to alloc a new space dynamically, the board goes wrong and reset it self.

Thanks a lot

Answer 1

One thing that looks suspicious is that you convert char* buffer to (cb_tlv_node_t *) and try to use it. ARM requires that 32-bit integers are correctly aligned to 4-byte boundaries when accesing them. It is likely that buffer pointed by char *buffer is aligned to 1-byte boundaries. by user694733

so i changed this

typedef struct cb_ble_buffer_s {
    uint16_t total_length;
    uint16_t current_length;
    int8_t current_data_id;
    int8_t expect_package_id;
    char buffer[500];
} cb_ble_buffer_t;

into this

typedef struct cb_ble_buffer_s {
    uint16_t total_length;
    uint16_t current_length;
    int16_t current_data_id;
    int16_t expect_package_id;
    char buffer[500];
} cb_ble_buffer_t;

and it just works fine and steady many thanks to @user694733