Hi Chee,
>>I would like to know how to setup on custom board to use ADB ?
Android SDK and tools are included in Android Studio, so you should firstly install android Studio. Actuall you can get all related information from android website.
https://developer.android.com/studio
>>Do I need OTG board for the customer board for imx6dl.
USB on board should work in device mode.
Hope these information is helpful for you.
Have a nice day!
B.R,
Weidong
