* When you program in the arduino-cli

  In your sketch you simply put

    #include <U8g2lib.h>

    // U8G2_SH1106_128X64_NONAME_1_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);

    U8G2_SH1106_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);

    (The first is the low memory page mode. Second is standard and much better)


  The Arduino stuff is staged in .arduino15
  The Arduino stuff is installed in /home/greg/Arduino/libraries/U8g2/src/U8g2lib.h
                                                                          U8g2lib.cpp

  From looking at the .h file we see that

    U8G2_R0 is a pointer to a constant u8g2_cb_t structure

    U8G2_SH1106_128X64_NONAME_F_HW_I2C    is a derived class of U8G2

    it defines a public contructor of the same name

    
    U8G2_SH1106_128X64_NONAME_F_HW_I2C
    

    it calls 
      u8g2_Setup_sh1106_i2c_128x64_noname_f(&u8g2, rotation, u8x8_byte_arduino_hw_i2c, u8x8_gpio_and_delay_arduino);
      u8x8_SetPin_HW_I2C(getU8x8(), reset, clock, data);

    we can see it really then comes down defining two MCU specific functions

      u8x8_byte_arduino_hw_i2c

      u8x8_gpio_and_delay_arduino

    
 



  

  






  

* In order to get this tool chain to work

  sudo yum remove cmake
  sudo yum install cmake3
  cd /usr/bin
  sudo ln -s cmake3 cmake


* Compile and flash a program
 1002  cd eework/
 1003  cd hello_world
 1001  . $HOME/esp/esp-idf/export.sh
 1004  idf.py set-target esp32
 1009  \rm -rf build
 1010  idf.py set-target esp32
 1011  idf.py menuconfig
 1012  idf.py build
 1014  idf.py -p /dev/ttyUSB0 flash
 


* Install Tool Chain

https://docs.espressif.com/projects/esp-idf/en/latest/esp32/get-started/index.html#get-started-get-prerequisites

mkdir -p ~/esp
cd ~/esp
git clone --recursive https://github.com/espressif/esp-idf.git

cd ~/esp/esp-idf
./install.sh


******************************************

In the terminal where you will run code

cd xyz

. $HOME/esp/esp-idf/export.sh

alias get_idf='. $HOME/esp/esp-idf/export.sh'



cd ~/eework
cp -r $IDF_PATH/examples/get-started/hello_world .


cd hello_world
idf.py set-target esp32
idf.py menuconfig
idf.py build