On 10/4/2010 4:26 PM, Reinhard Meyer wrote: > Dear Wolfgang Denk, Vipin Kumar, >> >> In message <4ca9acaa.2020...@st.com> you wrote: >>>>> This writel results in writing byte by byte on the address pointed to by >>>>> status_reg. >>>>> This problem is visible with both gcc version 4.4.1 as well as 4.5.0 >>>> I bet this is on some ARM system? >>> Yes, it is on an ARM system (CortexA9). But I still feel that since I am >>> creating >>> a new u32 * status_reg, the code should not use any intelligence and use >>> the pointer >>> only to produce an str instruction in the form >>> str r0, [r1] >>> >>> But it retains the packed property of the structure even with a new u32 >>> ponter >>> typecasted to u32 * >>> u32 * status_reg = (u32 *)xyz->x; >>> >>> A writel to status_reg results in byte by byte writing > > How do you know that? Disassembly? Bus snooping? >
Disassembly >> >> I agree with you. I always considered such behaviour of the ARM C >> compiler a bug, and still do. However, people with better knowledge >> of the ARm architecture than me might be able to explain why the >> responsible PTB consider this to be a good and necessary "feature" of >> th compiler. > > Maybe because writel(v,a) is ultimately defined as > > (*(volatile unsigned int *)(a) = (v)) > > and the compiler has to assume the worst, i.e. that (a) is not word > aligned? Maybe there is a new compiler switch to turn that > "pessimisation" off? > I agree with you on this. But if I create a new u32 pointer and point to an element with in the packed structure, then what should be the behavior ? > On the other hand, if what you say were true, all code for AT91 that > uses writel() to access 32 bit only peripheral registers would not > work with those newer toolchains (still 4.2.4 here). > Yes, if the at91 code is using packed attribute for device structures Regards Vipin _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot