Hi,
root:/> Oops: Exception in kernel mode, sig: 4
r1: 00000004 r2: cfc1e008 r3: 00000004 r4: 00000000
r5: cfc1ffa4 r6: 00000001 r7: 00000001 r8: 00000000
r9: c8734894 r10: 00000004 r11: 00000004 r12: 01000000
r13: 00000400 r14: 00000000 r15: d9274300
ra: c8000bbc fp: 00000000 sp: cfc1fe3c gp: 0000ca80
ea: c8002440 estatus: 00000001
Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
Maybe sig:4 means that the CPU encounters an illegal instruction, so please get its objdump file like
nios2-***-linux-gnu-objdump -d -S vmlinux > vmlinux.objdump
and check whether the instruction located at 0xc8002440 is illegal or not. If the instruction is legal, I recommend you once to check the timing of SDRAM I/Os etc.
Kazu