EFR32BG21 Series 2 BLUETOOTH® Wireless SoCs Silicon Labs EFR32BG21 Series 2 BLUETOOTH® Wireless SoCs offer an 80MHz ARM Cortex-M33 core with a high-performance 2.4GHz radio to provide an industry-leading, energy-efficient wireless SoC for IoT-connected applications. The EFR32BG21 Blue Gecko wireless SoCs are designed to increase processing capability, improve RF performance, and lower active current while providing a higher level of security.