TM4C1294 + CC3100 SPI speed problem

hi

i use the SW package:

C:\TI\tirtos_tivac_2_12_01_33\packages\examples\source\udpEchoCC3100

my HW is TM4C1294 Launchpad + CC3100BOOST,

I encounter a problem that the SPI interface between TM4C1294 and CC3100 always fail within 5~20 sec under contineous communication.

And I found the sample code setting the SPI clock speed as 14Mbps, when i try to lower the speed to 2Mbps, it will get fail within approx half hour.

any hint to solve this problem?