Merge pull request #83 from fdlamotte/configure-cpu-frequency-at-build-time-for-esp32

Add an ESP32_CPU_FREQ build flag to lower freq

platformio.ini

@@ -31,6 +31,8 @@ extends = arduino_base
 platform = espressif32
 monitor_filters = esp32_exception_decoder
 extra_scripts = merge-bin.py
+build_flags = ${arduino_base.build_flags}
+;  -D ESP32_CPU_FREQ=80          ; change it to your need
 build_src_filter = ${arduino_base.build_src_filter}
 
 ; ================

src/helpers/ESP32Board.h

@@ -17,6 +17,10 @@ public:
     // for future use, sub-classes SHOULD call this from their begin()
     startup_reason = BD_STARTUP_NORMAL;
 
+  #ifdef ESP32_CPU_FREQ
+    setCpuFrequencyMhz(ESP32_CPU_FREQ);
+  #endif
+
   #ifdef PIN_VBAT_READ
     // battery read support
     pinMode(PIN_VBAT_READ, INPUT);