Hi Omar,
Another issue that confuses me is how do I interface the ESP8266 with Hexiwear. It is true that Hexiwear uses MK64 MCU and I have tried using processor expert to change the pin configurations of the ESP8266 by following the tutorial you provided.
I used a separate provided source code FDRM-K64F_ESP8266 from github and I tried configuring the pins to UART3 successfully. I also managed to build it without any errors. However, when I copy these files into my Hexiwear_MK64 source code files to run them I would encounter errors. I am not entirely sure how to interface the given ESP8266 code into my given Hexiwear code. It would be helpful if you could guide me with this.
Thank you.
Mark