Re: Assembler in C under Linux

[martin.kahlert@keksy.mchp.siemens.de (Martin Kahlert)]

[Posted and mailed]

In article < slrn84dhpn.ihf.mperrin@hcs.harvard.edu >,
	mperrin@hcs.harvard.edu (Marshall Perrin) writes:
> I'm trying to port a driver for a digital signal processor card from
> DOS to Linux. The DOS driver, developed by someone not me ;-), is
> mostly C but has a fair amount of inline assembler.  For Borland C for 
> DOS, this was pretty easy to do. Just
>   asm {
>       mov dx, DSP_BaseIO
>       add dx, reg_offset
>  }
> etc etc.
> 
> Gcc of course chokes on the above. I've attempted to read through the gcc
> documentation and figure out how to do this, but no luck. That led me 
> towards something like
> 
>     asm("mov dx, %0" : : "d" (DSP32C_BaseIo));
>     asm("add dx, %0" : : "d" (reg_offset));
>     asm("in ax,dx");
>     asm("mov %0,ax"  :"=d" (value) : );

The (hopefully) correct syntax for these lines would be
something like:

#include <stdio.h>

int main(int argc,const char *argv[])
{
 short int DSP32C_BaseIo=18,reg_offset=15,value;
 asm("inw %1, %0" : "=r" (value) : "r" (DSP32C_BaseIo+reg_offset));

 printf("value=%d\n",value);
 return 0;
}

Then gcc -O -o prog prog.c
         ^^^ important!
This prog doesn't work!

In LINUX you can't directly access the hardware.
Write a driver, or write a setuid root program.

All the stuff the asm does could be done easily
and much more portable in C.
For that read 
http://www.linuxdoc.org/HOWTO/mini/IO-Port-Programming.html
first.

Hope that helps,
Martin.