How to specify entry point using CCSv5 and MSP430 linker v4.2.1

Hi Steve,

Maybe something in your project setting would be needed as well. Your comment reminded me of something from earlier this year:

RE: Creating a custom BSL for firmware update - MSP low-power microcontroller forum - MSP low-power microcontrollers...

e2e.ti.com

Other Parts Discussed in Thread: MSP430FR5969 , MSP430FR5739 I downloaded MSPBoot 1_01_00_00 from link ‘’ and tried to build MSPBoot on CCS version 6.0 with TI

I took a look at boot.c in the run time support library. I'm using a newer compiler version, but hopefully this hasn't changed much. I can find the rts library source code in my ccsv6 installation at C:\ti\ccsv6\tools\compiler\msp430_4.2.6\lib\src. Looking in boot.c, I see this:

/*****************************************************************************/
/* C_INT00() - C ENVIRONMENT ENTRY POINT                                     */
/*****************************************************************************/
#pragma CLINK(_c_int00)
CSTART_DECL _c_int00()
{
   STACK_INIT();
   
   /*------------------------------------------------------------------------*/
   /* Allow for any application-specific low level initialization prior to   */
   /* initializing the C/C++ environment (global variable initialization,    */
   /* constructers).  If _system_pre_init() returns 0, then bypass C/C++     */
   /* initialization.  NOTE: BYPASSING THE CALL TO THE C/C++ INITIALIZATION  */
   /* ROUTINE MAY RESULT IN PROGRAM FAILURE.                                 */
   /*------------------------------------------------------------------------*/
   if(_system_pre_init() != 0)  _auto_init();

   /*------------------------------------------------------------------------*/
   /* Handle any argc/argv arguments if supported by an MSP430 loader.       */
   /*------------------------------------------------------------------------*/
   _args_main();

   exit(1);
}

Then looking in boot.h, I see STACK_INIT() is really just defined as:

/*---------------------------------------------------------------------------*/
/* Macro to initialize stack pointer.  Stack grows towards lower memory.     */
/*---------------------------------------------------------------------------*/
#if defined(__LARGE_DATA_MODEL__)
#define STACK_INIT() __asm("\t   MOVX.A\t   #__STACK_END,SP")
#else
#define STACK_INIT() __asm("\t   MOV.W\t    #__STACK_END,SP")
#endif

So I think really the only thing that STACK_INIT() actually changes is the value of the SP register. You could simply change it back to wherever else you want (wherever maybe you know you have space in RAM to have stack while you are doing your copy to NVM?) in _system_pre_init, and I don't think that should really have changed anything in RAM.

As a note, this is actually what our new Compute Through Power Loss (CTPL) library does (it is part of our new MSP-FRAM-UTILITIES for FRAM devices). That library is using _system_pre_init to bypass our normal c-startup code variable initialization etc, because in that case we are wanting to copy the variables and peripheral states that we saved to FRAM as we were losing power back into the peripheral registers and RAM, rather than using initial startup values - this includes the stack being initialized to the same state it was in as we were losing power. So that library simply lets the STACK_INIT() call in _c_int00 occur, but then in _system_pre_init simply reinitializes the SP (and stack values in RAM) to whatever we'd saved.

Regards,

Katie

Katie,

Again, thank you for the quick response.

I do understand that STACK_INIT() only modifies the stack pointer, but the SP is the most important bit of state information that we are trying to preserve, as the purpose of saving RAM is for crash analysis. We absolutely must be able to specify our own entry point for this reason.

- Steve