1、PC端 https://github.com/cidadao/efm32_loader

http://theramblingness.com/2015/07/16/a-gui-and-cli-utility-for-efm32s-uart-bootloader/

support for USB and uart bootloader,run in CLI or GUI mode.

2、MCU端 http://www.silabs.com/Support%20Documents/TechnicalDocs/AN0003.pdf