Reference documents

Allwinner V40 datasheet:

https://drive.google.com/file/d/0B4PAo2nW2KfneE54VzVOdHpITzA/view?usp=sharing

Allwinner R40 datasheet:

https://drive.google.com/file/d/0B4PAo2nW2KfnbVp2TmRMYUdPUGM/view?usp=sharing

Allwinner R40 User Manual v1.0

https://github.com/tinalinux/docs/blob/r40-v1.y/Allwinner_R40_User_Manual_V1.0.pdf

axp221s PMU datasheet:

https://drive.google.com/file/d/0B4PAo2nW2KfnM2pnT19zZW5qOTA/view?usp=sharing