In XC16 (for the 16-bit dspic33E***MU8xx and MC family) I use union QEICounter and similar unions to convert two 16-bit words (e.g. read from UDP/serial) to 32-bit int32_t or ulong, which is defined like this:

typedef union
{
    struct
    {
        unsigned int  loWord;           // Counter high word
        unsigned int  hiWord;           // Counter low word
    }f;                             // field access
    unsigned int      w[2];         // 16 bits access
    unsigned long      l;           // 32 bits access   
}qeiCounter;

I noticed that sometimes the compiler apparently doesn’t link the w field writes to the l read with repeated usage. I tried declaring the union variable with volatile, and that apparently does not solve it either.

Any idea how to properly do this? I adopted the union trick from older Microchip libraries (plib,MLA)

I’m still in transition from xc16 to xcdsc, so anything that works on both would be great.