Hi qihui you, I guess you chip doesn't have 1MB flash and you are using GCC. 

If that's true, it's a known issue. The workaround is to replace the linker file C:\SiliconLabs\SimplicityStudio\v4\developer\sdks\gecko_sdk_suite\v2.7\platform\Device\SiliconLabs\EFR32MG21\Source\GCC\efr32mg21.ld with the attached one.

After that, clean and rebuild your project.

Please let me know if it works.

Hi YK, sorry for the late response. I spent some time investigating this, and I found that it only happens when the debug interface is connected. In that case, the device will enter a special energy mode (between EM1 and EM2). In that mode, the clock is still running. 

The code snippet you provided is a good workaround for this case.  

Hi Daemon and YK,  I can reproduce this issue with my BRD4181A. 

Currently I don't know the root cause. The workaround is to perform a reset or power cycle after you flashed something with J-Link.

@Gary, I think so, but not sure about it. That's why I suggest you contact our sales.

@YK, I think you can contact the sales or distributors to check if there will be video recordings. 

Hi Gary, it's a training about low cost gateway design held in China, in the end of June, 2020. 

The little box in the picture is the low cost gateway. 

Hi Victor Marcon, There will be a training about it in Shenzhen, China.