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Overlapping Memory areas in ARM

Irvin Jasper Cerdan over 14 years ago

Hi,

Is there a way to allow memory overlapping in MDK-ARM?

I have tried to use the "__attribute__((at(address)))" but it does not work.

Ex.

unsigned char array1[20] __attribute__((at(0x20002000)));
unsigned char array2[10] __attribute__((at(0x2000200A)));

Parents

0 ImPer Westermark over 14 years ago in reply to Irvin Jasper Cerdan

And what do you think you can do with pointers?

Such as:

typedef struct {
    ....
} my_strange_thing_1;

typedef struct {
    ....
} my_strange_thing_2;

typedef struct {
    ....
} my_strange_thing_3;

uint8_t bulk[BULK_SIZE];

my_strange_thing_1 *strange_ref1;
my_strange_thing_2 *strange_ref2;
my_strange_thing_3 *strange_ref3;

void map_strange1(void) {
    assert(BULK_SIZE >= sizeof(my_strange_thing_1);
    strange_ref1 = my_strange_thing_1;
    strange_ref2 = NULL;
    strange_ref3 = NULL;
}

void map_strange2(void) {
    assert(BULK_SIZE >= sizeof(my_strange_thing_2);
    strange_ref1 = NULL;
    strange_ref2 = my_strange_thing_2;
    strange_ref3 = NULL;
}

void map_strange3(void) {
    assert(BULK_SIZE >= sizeof(my_strange_thing_3);
    strange_ref1 = NULL;
    strange_ref2 = NULL;
    strange_ref3 = my_strange_thing_2;
}

enum Strange {
    STRANGE_FREE,
    STRANGE_1,
    STRANGE_2,
    STRANGE_3
};




struct {
    Strange mapped;
    union {
        my_strange_thing_1 strange1;
        my_strange_thing_2 strange2;
        my_strange_thing_3 strange3;
    }
} strange_overlapping_data;

Reply

0 ImPer Westermark over 14 years ago in reply to Irvin Jasper Cerdan

And what do you think you can do with pointers?

Such as:

typedef struct {
    ....
} my_strange_thing_1;

typedef struct {
    ....
} my_strange_thing_2;

typedef struct {
    ....
} my_strange_thing_3;

uint8_t bulk[BULK_SIZE];

my_strange_thing_1 *strange_ref1;
my_strange_thing_2 *strange_ref2;
my_strange_thing_3 *strange_ref3;

void map_strange1(void) {
    assert(BULK_SIZE >= sizeof(my_strange_thing_1);
    strange_ref1 = my_strange_thing_1;
    strange_ref2 = NULL;
    strange_ref3 = NULL;
}

void map_strange2(void) {
    assert(BULK_SIZE >= sizeof(my_strange_thing_2);
    strange_ref1 = NULL;
    strange_ref2 = my_strange_thing_2;
    strange_ref3 = NULL;
}

void map_strange3(void) {
    assert(BULK_SIZE >= sizeof(my_strange_thing_3);
    strange_ref1 = NULL;
    strange_ref2 = NULL;
    strange_ref3 = my_strange_thing_2;
}

enum Strange {
    STRANGE_FREE,
    STRANGE_1,
    STRANGE_2,
    STRANGE_3
};




struct {
    Strange mapped;
    union {
        my_strange_thing_1 strange1;
        my_strange_thing_2 strange2;
        my_strange_thing_3 strange3;
    }
} strange_overlapping_data;

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