Atmel SAMD20 sleeps in standby mode on mynewt

[edward-jw-yu]

newt version
Apache Newt version: 1.4.1

Atmel
SAMD20E18

After calling
system_set_sleepmode(SYSTEM_SLEEPMODE_STANDBY); system_sleep();
the system successfully went to sleep.
When I pressed the button to wake it up, It did wake up, But after a very little while, it crashed.
I used the atmel studio project to test about the sleep, it was fine.

Here I would like to learn about the sleep about mynewt.
Before sleep and After wake up, It needs to do something ?

Thanks a lot.