Problem with using asm code in C

biralti · ‎2010-08-05

Posted on August 05, 2010 at 16:10

chikos332 · ‎2011-05-17

Posted on May 17, 2011 at 14:01

Hi,

You can use an assembler function with one argument. The first argument is always loaded in register r0 of the core so you can directly handle this register:

example:

uint8_t __FUNCTION(uint8_t tmp)

{

__ASM(''INSTRUCTION r0, r0'');

__ASM(''bx lr'');

}

Cheers.

picguy2 · ‎2011-05-17

Posted on May 17, 2011 at 14:01

In chikos’s example the value of tmp is passed to the subroutine. The address of tmp is what is wanted. I.e. call with &tmp and adjust the function header to expect an address.

In IAR tools click on Help -> C/C++ development guide. This opens up a pdf. Search INLINE ASSEMBLER using case sensitivity.

It seems that the only way IAR’s C/C++ inline asm(“...�?) can know about variable address is via a DCD statement. I would suspect that local (stack allocated) variables might not work.

So I tried in EWARM v5.4 and it looks like even the example in the pdf does not work. FWIW I also tried mov32. It didn’t work either.

Andrew Neil · ‎2011-05-17

Posted on May 17, 2011 at 14:01

Why do you want to use inline assembler anyhow?

Why not create a proper assembler module, wth an assembler function that you can call from 'C' ?

biralti · ‎2011-05-17

Posted on May 17, 2011 at 14:01

I want address of the variable instead of its value. Also i couldn't run this code. I use Ride7.

thanks for the answer.

biralti · ‎2011-05-17

Posted on May 17, 2011 at 14:01

I use Ride7. I searched ''assembler'' in help files and i found somethings but in examples always RAM addresses was used for assign a value to variable. I couldn't send variable address to asm code. I try ''#define'' directive for obtain an address of variable but i couldn't use it in asm.

Thanks for your answer

biralti · ‎2011-05-17

Posted on May 17, 2011 at 14:01

How could i do this? Can you give any example?

John F. · ‎2011-05-17

Posted on May 17, 2011 at 14:01

Hi,

You could pass the address of the variable as your function argument.

example:

uint8_t temp;

//call as ...

FUNCTION(& temp);

//function argument is pointer to variable (its address)

uint8_t __FUNCTION(uint8_t * tmp)

{

__ASM(''INSTRUCTION r0, r0'');

__ASM(''bx lr'');

}