9.11.11 Space Variable Attribute

The space(memory-space) attribute can be used to direct the compiler to allocate a variable in a specific memory space. Valid memory spaces are prog for program memory, data for data memory, and serial_mem for serial memory such as SPI Flash. The data space is the default space for non-const variables.

The prog, data, and serial_mem spaces normally correspond to the kseg0_prog_mem, ksegN_data_mem, and serial_mem memory regions, respectively, as specified in the default device-specific linker scripts.

This attribute also controls how initialized data is handled. The linker generates an entry in the data-initialization template for the default space(data). But, it does not generate an entry for space(prog) or space(serial_mem), since the variable is located in non-volatile memory. Typically, this means that space(data) applies to variables that will be initialized at runtime startup; while space(prog) and space(serial_mem) apply to variables that will be programmed by an in-circuit programmer or a bootloader.

const unsigned int __attribute__((space(prog))) jack = 10;
const unsigned int __attribute__((space(serial_mem))) zori = 1;
signed int __attribute__((space(data))) oz = 5;