我是个DSP新手，还没入门，用6678的EVM调试SRIO ，例程为网上下载的Keystone例程，调试出现下面的情况：
Enable Exception handling...
External exception happened. MEXPFLAG[3] = 0x200000.
Event 117: UMC_ED2 Uncorrected bit error detected
Enter LL2 EDC handler, but no error flag is set!
NRP=0xc046cf8, NTSR=0x1000d, IRP=0x0, ITSR=0x0, TSCH=0x0, TSCL=0x42066
B3=0xc046c94, A4=0x1, B4=0x3, B14=0x8254c8, B5=0x8231d8
SRIO_DIGITAL_LOOPBACK test start................................................................................................
Initialize DSP main clock = 100.00MHz/1x10 = 1000MHz
Initialize DDR speed = 66.67MHzx/1x20 = 1333.333MTS
DDR3 leveling has failed, STATUS = 0x40000064
请教一下这是什么原因导致的？应该怎么解决？