Undocumented SDR receive mode found in ESP32 chips

Two independent researchers discovered an undocumented mode in ESP32 chips that taps the I/Q stream before the Wi-Fi modem, letting the microcontroller act as an SDR receiver. It works on chips with earlier Tensilica hardware and supports 2.4 and 5 GHz bands, but receive only.

• Mode taps I/Q stream before the Wi-Fi modem for external processing
• Works on ESP32 chips with Tensilica hardware, including early revisions
• Supports 2.4 and 5 GHz depending on the chip
• Receive only, no transmit capability