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cpointerstypescastingmsp430

Why is this showing "Invalid type conversion"?

I have this piece of C code (For MSP430 platforms, cl430 compiler):

void function(uint8_t * x){
    // This variable is defined in the linker file as "X_ADDR = 0xE000;"
    extern uint32_t X_ADDR; 
    uint16_t i = 0;
    uint16_t size = 10;
    uint32_t dst_addr = (uint32_t) &X_ADDR; 

    for (i=0; i < size; i++){
         *((uint8_t *) (dst_addr+i)) = *(x+i); // <-- This line shows the warning
}

What I understand is this, but here is where I guess I am wrong:

*((uint8_t *) (dst_addr+i)) = *(x + i);
                |       |       |   |
                V       V       V   V
*((uint8_t *) (u32  + u16)) = *(u8*+u16);
       *((uint8_t *) (u32)) = *(u8*);
                     *(u8*) = u8;
                         u8 = u8;

This platform is 16-bits but it supports an extended addressing mode of 20-bits.

Any hint on this? and how should it be done instead? Thanks in advance

Solution

  • You seem to get this on 64 bit compilers that use 64 bit pointers. Converting a 32 bit integer to a 64 bit pointer is questionable and non-portable.

    Correct this by using the portable integer type meant to be used for this very purpose:

    uintptr_t dst_addr = 0x00FFABCD;

    Now it will compile cleanly on all mainstream 64 bit compilers. Tried on gcc, clang icc with -std=c11 -Wextra -Wall -pedantic-errors, no problems.

    In addition, when accessing an absolute address, you will almost certainly need to volatile qualify the pointer.