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Altera_Forum's avatar
Altera_Forum
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20 years ago

How to jump to labels which are defined in C code

Hi,

In order to speed up system, I write a routine in ASM instructions. Then in asm code, I intend to jump to a label named LOOP which is defined in C code, but I failed. The following error occur:

void Fast_Copy_In_ASM(alt_u32* pSource, alt_u32* pDest, alt_u32 length)

{

LOOP:

asm("ldwio r7,0(r4)");

asm("stwio r7,0(r5)");

asm("addi r5,r5,4");//increase read_data to point to next byte

asm("addi r4,r4,4");//increase read_data to point to next byte

asm("addi r6,r6,-4");//decrease read_length

asm("bne r6,zero,LOOP ");//CWG2

}

error:undefined reference to ‘LOOP’

(1)How to jump to labels which are defined in C code from asm instruction?

(2)Also, pls kindly tell me does there exist any document related to C and ASM mixture coding?

Thanks any help!

David http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/tongue.gif

9 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    20 years ago

    That is basically inline GCC assembly... that follow the rules of GCC ... you can find many information on the web just searching for "inline gcc assembler" :-)

    bye,

    Paolo
  • Altera_Forum's avatar
    Altera_Forum
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    20 years ago

    > error:undefined reference to ‘LOOP’

    Put the label inline as well: <div class='quotetop'>QUOTE </div>

    --- Quote Start ---

    asm volatile (

    "LOOP: ldwio r7,0(r4)"

    " stwio r7,0(r5)"

    " addi r5,r5,4"

    " addi r4,r4,4"

    " addi r6,r6,-4"

    " bne r6,zero,LOOP " \

    );[/b]

    --- Quote End ---

    Regards,

    --Scott
  • Altera_Forum's avatar
    Altera_Forum
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    20 years ago

    Hi Scott:

    I have tried your code, no compiling error occurred,but something was wrong.

    The following code work fine.

    asm("Fast_Copy_In_ASM_Loop: ldwio r7,0(r4)");

    asm("stwio r7,0(r5)");

    asm("addi r5,r5,4");//increase read_data to point to next byte

    asm("addi r4,r4,4");//increase read_data to point to next byte

    asm("addi r6,r6,-4");//decrease read_length

    asm("bne r6,zero,Fast_Copy_In_ASM_Loop");//CWG2

    But the code you showed me were all skipped when I step into it.

    asm volatile (

    "LOOP: ldwio r7,0(r4)"

    " stwio r7,0(r5)"

    " addi r5,r5,4"

    " addi r4,r4,4"

    " addi r6,r6,-4"

    " bne r6,zero,LOOP " \

    );

    WHY?

    best regards,

    David
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    20 years ago

    > But the code you showed me were all skipped when I step into it.

    ...

    > WHY?

    You might be stepping through each statement rather than each instruction.

    Each "asm" is treated as a statement..

    Regards,

    --Scott
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    20 years ago

    Hi Scott:

    But I can&#39;t find the corresponding code in Disassembly window.

    So it might be optimized, am I right?

    But my optimization level is -O0.

    Can you help me to try the code?

    SOURCE CODE

    void Fast_Copy_In_ASM(alt_u32* pSource, alt_u32* pDest, alt_u32 length)

    {

    asm volatile (

    "Fast_Copy_In_ASM_Loop1: ldwio r7,0(r4)"

    " stwio r7,0(r5)"

    " addi r5,r5,4"

    " addi r4,r4,4"

    " addi r6,r6,-4"

    " bne r6,zero,Fast_Copy_In_ASM_Loop1 " \

    );

    //asm("Fast_Copy_In_ASM_Loop: ldwio r7,0(r4)");

    //asm("stwio r7,0(r5)");

    //asm("addi r5,r5,4");//increase read_data to point to next byte

    //asm("addi r4,r4,4");//increase read_data to point to next byte

    //asm("addi r6,r6,-4");//decrease read_length

    //asm("bne r6,zero,Fast_Copy_In_ASM_Loop");//CWG2

    }

    Disassembly code

    <span style="color:red"><span style="color:blue">void Fast_Copy_In_ASM(alt_u32* pSource, alt_u32* pDest, alt_u32 length)

    {

    10053f4: defffc04 addi sp,sp,-16

    10053f8: df000315 stw fp,12(sp)

    10053fc: d839883a mov fp,sp

    1005400: e1000015 stw r4,0(fp)

    1005404: e1400115 stw r5,4(fp)

    1005408: e1800215 stw r6,8(fp)

    0100540c <Fast_Copy_In_ASM_Loop1>:

    asm volatile (

    100540c: 29c00037 ldwio r7,0(r5)

    "Fast_Copy_In_ASM_Loop1: ldwio r7,0(r4)"

    " stwio r7,0(r5)"

    " addi r5,r5,4"

    " addi r4,r4,4"

    " addi r6,r6,-4"

    " bne r6,zero,Fast_Copy_In_ASM_Loop1 " \

    );

    //asm("Fast_Copy_In_ASM_Loop: ldwio r7,0(r4)");

    //asm("stwio r7,0(r5)");

    //asm("addi r5,r5,4");//increase read_data to point to next byte

    //asm("addi r4,r4,4");//increase read_data to point to next byte

    //asm("addi r6,r6,-4");//decrease read_length

    //asm("bne r6,zero,Fast_Copy_In_ASM_Loop");//CWG2

    }

    1005410: df000317 ldw fp,12(sp)

    1005414: dec00404 addi sp,sp,16

    1005418: f800283a ret</span></span>

    Thanks a lot!

    David
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    20 years ago

    Duh ... sorry :

    <div class='quotetop'>QUOTE </div>

    --- Quote Start ---

    asm volatile (

    "0: ldwio r7,0(r4) \n"

    " stwio r7,0(r5) \n"

    " addi r5,r5,4 \n"

    " addi r4,r4,4 \n"

    " addi r6,r6,-4 \n"

    " bne r6,zero,0b \n"

    );[/b]

    --- Quote End ---

    Regards,

    --Scott