Am 21.12.2010 13:51, schrieb Albert ARIBAUD: > Le 21/12/2010 13:35, Alexander Holler a écrit : > >> Hmm, is there actual somethinbg which should forbid the compiler to >> generate such code which rereads something? It might not be nice, but I >> don't think that it is forbidden for a compiler to do so. So the proper >> way to handle such, might be to use asm to avoid that the compiler >> touches that register. > > Yes there is something that should prevent a compiler from inserting > reads: these accesses are to hardware, not memory, and may cause side > effects even on read (these could be acknowledges, for instance; I've > seen instances of that myself on some HW). > > Another way to look at it is that the semantics of " *ptr = value " is a > pure write and should not result in a write-then-read.
I think it's something like atomic_read. E.g. when reading an 32bit int (uint32_t i = *bla;), nothing forbids that the compiler generates code which reads those 4 bytes byte by byte (and so becoming a non-atomic operation). It's unusual to do so on 32bit architectures but valid. Regards, Alexander _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
