The interrupt vectors for the MSP430 and MSP430X devices are 16 bits. Therefore, interrupt service routines (ISRs) must be placed into the low 64K of memory. Convenience macros are provided in the MSP430X device headers file to declare interrupts to ensure 16-bit placement when linking.
Alternatively, use the CODE_SECTIONS pragma to place the code for ISRs into sections separate from the default .text sections. Use the linker command file and the SECTIONS directive to ensure the code sections associated with ISRs are placed into low memory.
If you do not specify an ISR for some interrupt vectors, an ISR will be provided for those vectors from the RTS library and the RTS library will automatically be linked with your application. The default ISR puts the device in low power mode. You can override the ISR provided by the RTS with the pragma vector and the unused_interrupts keyword as shown in Section 5.12.31.