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How can I accessing a variable in Assembler Code ?

pvp special

I use #pragma asm/#pragma endasm to embed Assembler Code in C Function.

My question is:

How can I accessing a variable in Assembler Code,which define by C code.

Just like this:

I need height speed to accessing XDATA from Addr 0x0000.

void Func()
{

unsigned char Var_C,i=0;

#pragma asm

mov DPTR,#0x0000

#pragma endasm

while(i++ < 0x10)

{

Var_C = ReadOneByte();

if(Var_C == 0xff)

{

Var_C = 0;

}

#pragma asm

MOV A,Var_C /* This line is not work */

MOVX @DPTR,A

INC DPTR

#pragma endasm

}

}

Build target 'Target 1'

compiling main.c...

main.src(181): error A45: UNDEFINED SYMBOL (PASS-2)

Thanks!!!

Parents
  • 0 in reply to Andy Neil

    "I need height speed to accessing XDATA from Addr 0x0000."

    It's hard to see what your code is actually doing, because you didn't follow the instructions when posting it - see above.

    Anyhow, it seems very unlikely that you are going to gain any advantage by simply throwing odd bits of inline assembler into your 'C' source.

    For a start, if speed is what you need, then a function call is not the way to read a single byte!

    Have you read "Writing Optimum Code" in the Manual?

    http://www.keil.com/support/man/docs/c51/c51_xc.htm

    Have you enabled optimisation & examined the code that the compiler generates? It could well be pretty good anyhow!

    If not, you probably need to write the whole function in assembler.

Reply
  • 0 in reply to Andy Neil

    "I need height speed to accessing XDATA from Addr 0x0000."

    It's hard to see what your code is actually doing, because you didn't follow the instructions when posting it - see above.

    Anyhow, it seems very unlikely that you are going to gain any advantage by simply throwing odd bits of inline assembler into your 'C' source.

    For a start, if speed is what you need, then a function call is not the way to read a single byte!

    Have you read "Writing Optimum Code" in the Manual?

    http://www.keil.com/support/man/docs/c51/c51_xc.htm

    Have you enabled optimisation & examined the code that the compiler generates? It could well be pretty good anyhow!

    If not, you probably need to write the whole function in assembler.

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