[U-Boot-Users] v2p4 porting troubles

[Wolfgang Denk]

In message <009b01c40baa$a324f2b0$cb01a8c0 at xiphos.ca> you wrote:
> We're doing quite the tag team here.

;-)

> 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));
> }

This code is broken. The "r" operand specification sais  "a  register
operand  is  allowed  provided  that it is in a general register." Of
course R0 is a GPR as well. I think you need to use "m" (any kind  of
address that the machine supports in general) here:

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

> But why?  What is it about this C code which causes this sort of thing?

Actually this is no C code, but inline assembler. And yes, it is  the
code, which uses an inappropriate operand specification.

> What constraints should be used? Where is decent, unambiguous documentation

Use "m".

> of gcc inline assembler (instead of poorly explained examples)?

The GCC info pages are  pretty  useful.  See  File:  gcc.info,  Node:
Simple Constraints,

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

I'm glad if I could help.

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
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