参照C6678开发板设计的电路板，SRIO/DDR测试无误.
按照Keystone I软件开发包里网口例程进行C6678 SGMII loopback测试，出现如下问题：
第1种结果：
[C66xx_0] Initialize DSP main clock = 100.00MHz/1x10 = 1000MHz
Initialize PASS clock = 100.00MHzx21/2 = 1050.000MHz
Initialize DDR speed = 100.00MHzx40/3 = 1333.333MTS
Enable Exception handling...
GE 1000M fullduplex internal SGMII loopback test...
waiting for GE RX interrupt timeout!
STATSA.RxGoodFrames =1
STATSA.RxOctets =82
STATSA.Frame65t127 =1
STATSA.NetOctets =82
SGMII port 1 is in the idle state.
第2中结果：
Initialize DSP main clock = 100.00MHz/1x10 = 1000MHz
Initialize PASS clock = 100.00MHzx21/2 = 1050.000MHz
Initialize DDR speed = 100.00MHzx40/3 = 1333.333MTS
Enable Exception handling...
GE 1000M fullduplex internal SGMII loopback test...
waiting for GE RX interrupt timeout!
number of descriptors in host queue DDR_HOST_SIZE1_FDQ (2059) changed from 256 to 255
0x82344021->0x82344041->0x82344061->0x82344081->0x823440a1->0x823440c1->0x823440e1->0x82344101->0x82344121->0x82344141->...
第3中结果：
Initialize DSP main clock = 100.00MHz/1x10 = 1000MHz
Initialize PASS clock = 100.00MHzx21/2 = 1050.000MHz
Initialize DDR speed = 100.00MHzx40/3 = 1333.333MTS
Enable Exception handling...
GE 1000M fullduplex internal SGMII loopback test...
有时MAC/SGMII/SEDES loopback测试都能跑通，但有时出现以上三种不同测试结果，不知怎么回事.
