test code: static int buffer[128];
memcpy_test(int * p) { memcpy(buffer, p, 128); }
memcpy_test(0x00000000) ==> OK memcpy_test(0x00000001) ==> unalign fault
use MDK libc memcpy, when dst or src is align, auto higher optimization to used memcpy4.
but use instruction LDM. so, if the arg p is unalign, fault....
info: cortex-M3/M4 MDK 3.x/4.x/5.x
quote arm doc: The Cortex-M4 processor supports unaligned access only for the following instructions: • LDR, LDRT • LDRH, LDRHT • LDRSH, LDRSHT • STR, STRT • STRH, STRHT All other load and store instructions generate a UsageFault exception if they perform an unaligned access, and therefore their accesses must be address aligned
Unaligned LDM, STM, LDRD, and STRD instructions always fault irrespective of whether UNALIGN_TRP is set to 1.
Unless you set your warning level dangerously low, you got a compiler warning about using an integer where a pointer was supposed to be, on the very line that caused the problem.
You should have heeded that warning.