[U-Boot-Users] possible ELDK4 gcc compiler bug

Tolunay Orkun listmember at orkun.us
Thu Dec 7 17:42:39 CET 2006

Matthias Fuchs wrote:
> Hi,
> I noticed some strange behavior when using the ELDK4 gcc for compiling 
> U-Boot for a (new) 405 target based on the current PMC405 board.
> The code needs to read-modify-write a memory mapped FPGA internal register.
> But the FPGA access does not appear in the object and therefore it is never 
> done.
> Here are some code snippets:
> 1) my 'fifo' BSP command:
> int do_fifo(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
> {
> 	struct pmc405v2_fpga_s *fpga = (struct pmc405v2_fpga_s *)FPGA_BA;
> 	int i;
> 	int n = 0;

The compiler is optimizing away your code. Check out the 'volatile' 
keyword. It is exactly this situation it was intended. A better way is 
to use in32() out32() etc. The I/O accessors make sure I/O operation is 
completed before next instruction is executed. Simply accessing the 
memory mapped registers might not archive the same.

Best regards,

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