On 25/01/2011 10:37, Cedric Roux wrote:
On 01/25/2011 09:04 AM, kevin diggs wrote:
Hi,
The function in question is returning the value of the PLL config
register in a PowerPC 750GX. I wanted to make sure that the optimizer
does not move or eliminate the call. I thought that is one of the uses
of the volatile qualifier???
Thanks!
kevin
static inline volatile unsigned int get_PLL(void)
{
unsigned int ret;
__asm__ __volatile__ ("mfspr %0,%1":
"=r"(ret):
"i"(SPRN_HID1)
);
return ret;
}
I think that SPRN_HID1 has to be declared as volatile
(if that has a meaning at all in your case) for gcc
to force the load in all cases (my .02 euros, I don't
know your target asm, I don't know what SPRN_HID1 is).
It's a PowerPC, and SPRN_HID1 is a constant (the "mfspr" instruction
reads from a specified "special purpose register").
Drop the "volatile" on the function declaration, and then code is then
correct. It is the "__volatile__" in the assembly statement that
ensures the read cannot be eliminated.
