Interface Problem

[Andreas Schwab]

"MUELLER,DAVID" <damuelle@ezinfo.ethz.ch> writes:

|> Hi
|> 
|> I have to program the onboard flash on an MPC8xx (PowerPC) based
|> system and i wish to write this program in C.
|> 
|> As no OS is running i have to use a background debugger.
|> Some services, offered by the Background Debugger Software,
|> expect some specific cpu register to contain the
|> paramters for the services. 
|> 
|> I though to be very clever if i do something like this.
|> 
|> Example:
|> 
|> /* constants (fcode) for Background Debugger (EBDS) */
|> #define QUIT      0
|> #define PUTS      1
|> 
|> /* call EBDS TRD function */
|> static __inline UINT32
|> Call_EBDS(UINT16 fcode)
|> {
|>   register UINT16 fcode_return __asm ("%r16");
|> 
|>   fcode_return = fcode;			// put function code in r16
|>   __asm volatile ("mfspr %r0, 82");	// call Background Debugger
|>   return(fcode_return);

You need to tell gcc that the asm is actually using and modifying the
register:

__asm volatile ("mfspr %%r0, 82" : "=r" (fcode_return) : "0" (fcode_return));

*Note Assembler Instructions with C Expression Operands: (gcc)Extended Asm.

-- 
Andreas Schwab                                      "And now for something
schwab@issan.cs.uni-dortmund.de                      completely different"
schwab@gnu.org