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Altera_Forum's avatar
Altera_Forum
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15 years ago

Nios2 stack size?

Hi all! I know this topic has been discussed more than once in this forum, but i did not find a sufficient answer. So please show mercy. Question: How do i find out how much memory is resevere...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

If you are being that careful/concerned about memory allocation then you'll almost certainly need to write your own startup code (rather than using the code that Altera's build system includes). This isn't that difficult as you only need to set the %gp and %sp (and maybe %et) registers from code at the cpu's reset entry point before jumping to the first C function.

This can be done from a .S file, but given the small number of instructions I hand assembled them and put them directly into the linker script. This gives something like (edited for inclusion here). 

MEMORY
{
        code_memory (x) : ORIGIN = 0x8000, LENGTH = 8k
        data_memory (rw) : ORIGIN = 0x14000, LENGTH = 48k
}
/* Memory from 0x14000 to 0x24000 is accessible from %gp */
_gp = 128k - 16k;
STACK_SIZE = 1024;
/* Constants for building instructions by hand */
RA_SHIFT = 32 - 5;
RB_SHIFT = RA_SHIFT - 5;
RC_SHIFT = RB_SHIFT - 5;
OP_SHIFT = RC_SHIFT - 6;
IMM16_SHIFT = 6;
SECTIONS
{
    /* code - at reset vector */
    code : {
        /* Instuctions to set %gp */
        LONG(0 << RA_SHIFT | 26 << RB_SHIFT | ((_gp + 32768) >> 16) << IMM16_SHIFT | 0x34)
        LONG(26 << RA_SHIFT | 26 << RB_SHIFT | (_gp & 0xffff) << IMM16_SHIFT | 0x4)
        /* Set %sp by adding affset from %gp */
        LONG(26 << RA_SHIFT | 27 << RB_SHIFT | 0x4 | ((stack_top - _gp) & 0xffff) << IMM16_SHIFT)
        LONG(main << 4 | 1)    /* jmpi main() */
        . = 0x20;
        /* Add exception (aka interrupt) code here */
        ....
        *(.text)
        /* add other sections */
    } >code_memory
    data : {
        stack_limit = .;
        . = . + STACK_SIZE;
        stack_top = .;
        *(.sdata*)
        *(.rodata)
        /* add other sections */
    } >data_memory
}