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RAM Placed in Fixed Location

Last modified by Microchip on 2024/01/19 00:09

You have the option to place specific Random Access Memory (RAM) variables at a fixed location within your source code. This forces the allocation of the variable to a fixed location so that it won't move between firmware versions. This is also useful for boot loaders or applications that are compiled separately and need to access a fixed-location communications register.

/*******************************************************************************
 *       RAM variables placed at a fixed location.
 *
 ******************************************************************************/

#if defined(__XC8__)
    #ifdef __CCI__
        unsigned char myRamVariable __at(0x20);
   #else
        unsigned char myRAMVariable @ 0x20;
   #endif

#elif defined(__XC16__)
/* it is strongly discouraged from placing variables at fixed addresses */
   #ifdef __CCI__
        unsigned char myRAMVariable __at(0x2000);
   #else
    /* the toolchain will place this at address 0x2000 even if that address does
        not exist on the device - we assume you know what you are doing */
   unsigned char myRAMVariable __attribute__((address(0x2000)));
   #endif

#elif defined(__XC32__)
/* Use absolute addresses, only when absolutely necessary as they can
   increase the size of the data-init table. */
   #ifdef __CCI__
        unsigned char myRAMVariable __at(0xA0001000);
   #else
        unsigned char myRAMVariable __attribute__((address(0xA0001000)));
   #endif

#endif