Atmel SAMD20 sleeps in standby mode on mynewt

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.

Start by reproducing the issue on the Atmel SAMD20E18 with system_set_sleepmode(SYSTEM_SLEEPMODE_STANDBY) and system_sleep(). Compare the wake-up behavior with the working Atmel Studio project and determine whether Mynewt requires any action before sleep or after wake. Done means identifying the cause of the post-wake crash or documenting the required sleep and wake sequence.

Written by the indexing model from the issue text.