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Hello all,

void select_next_task(void)
{
        if (l_task == 0)
        {
                l_task = 1 ;
        }
        else
        {
                l_task = 0 ;
        }
}

__asm void context_switch(void)
{
        STMDB R13!, {R0-R12, LR} ; save context

        BL        __cpp(select_next_task) ; select the next task to run

        LDR   R0,=__cpp(g_task_stacks)
        LDR   R1,=__cpp(&l_task)
        ADD       R0, R0, R1 ; calculate the offset of the next task stack
        LDR    R13, [R0] ; set the stack pointer to the new stack
        LDMIA R13!, {R0-R12, LR}
        BX                       LR        ; embedded assembly requires an explicit return instruction
}

I am trying change the context of my STR9. For that, I am working on a small prototype that I will extend later. The problem is that the marked like generates the following linker error:

scheduler.axf: Error: L6238E: context_switch.o(.emb_text) contains invalid call from '~PRES8' function to 'REQ8' function select_next_task.

If I comment the marked instruction, the program links corectly. I know what this is all about: assembler code (that does not preserve 8-byte stack alignment) calls compiled C/C++ code (that requires 8-byte stack alignment). But why is this caused only when I try to load SP with another address? Is this the proper way to do it? Are there any restictions on the address contained in SP?