u32 should be alligned ?

wadi · ‎2012-02-10

Posted on February 11, 2012 at 01:17

hello

One question:

when i am using:

char table[10];

(...)

*(unsigned int*)&table[1]=0x12345678;

should the pointer be dword alligned in RAMy ? Can I make safely such access?

Or it is forbidden in ARM architecture

thanks in advance

Tesla DeLorean · ‎2012-02-10

Posted on February 11, 2012 at 01:52

The Cortex-M3 supports unaligned writes, the ARM 7 and 9 do not. Writing such code is non-portable and inefficient, and therefore probably best avoided.

On ARM 7 and 9, you'd typically use a memcpy() construct, and if the compiler were smart enough it would in-line appropriate code for short copies and the target architecture.

http://www.arm.com/files/pdf/IntroToCortex-M3.pdf

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