[U-Boot-Users] v2p4 porting troubles

[Joshua Lamorie <jpl@xiphos.ca>]

We're doing quite the tag team here.

> > (notice that this is the XIo_Out32() function generated by Xilinx XPS)
> Which sort of code does this tool generate? C code? Then it would  be
> indeed  a compiler probile, and I definitely would like to see this C
> code.

The code from Xilinx is as follows...

void XIo_Out32(XIo_Address OutAddress, Xuint32 Value)
{
   __asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "r"
(OutAddress));
}

... which is called from a simple program (found at the end of this email).

When this is compiled with the Xilinx toolchain (gcc 2.95 I think), it
generates the 'real' assembler as follows.

stw r0,0(r9)

However, when we put this into a linux toolchain (crosstools 0.26, or ELDK
3.0) it generates it with r0 and r9 in the opposite spots.

stw r9,0(r0)

We can change the C code to

   __asm__ volatile ("stw %1,0(%0); eieio" : : "r" (OutAddress), "r"
(Value));

Which seems to generate it correctly with the linux tools.

We have added this same function inside u-boot to toggle some LEDs as we are
debugging, but without changing anything it generates assembler that uses r4
and r3 and not r0 and r9, so there is no chance of a problem.

But why?  What is it about this C code which causes this sort of thing?
What constraints should be used? Where is decent, unambiguous documentation
of gcc inline assembler (instead of poorly explained examples)?

Thank you Wolfgang for your help so far.  Your comments have been very
useful.

Joshua

The original test code is as follows.

#define XPAR_IOBRIDGEV2P_PLB_0_BASEADDR 0x40000000
typedef unsigned long   Xuint32;    /**< unsigned 32-bit */
typedef Xuint32 XIo_Address;

void XIo_Out32(XIo_Address OutAddress, Xuint32 Value);
int simpletest();

int _start() {
        simpletest(0,0);
}

int simpletest()
{
        int i,j,k;

        XIo_Out32(XPAR_IOBRIDGEV2P_PLB_0_BASEADDR, 0x55);
        while (1) {
                for (i=1; i<30000; i++) {
                        for (j=i; j<5000; j*=2) {
                                for (k=0; k<1000; k+=5) {
                                }
                        }
                        XIo_Out32(XPAR_IOBRIDGEV2P_PLB_0_BASEADDR, i&0xFF);
                }
        }
        return(0);

}

void XIo_Out32(XIo_Address OutAddress, Xuint32 Value)
{

   //__asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "r"
(OutAddress));
   __asm__ volatile ("stw %1,0(%0); eieio" : : "r" (OutAddress), "r"
(Value));
}