Verification IP for GPIO protocol
https://www.egr.msu.edu/classes/ece480/capstone/fall09/group03/AN_balachandran.pdf
http://www.testandverification.com/TVS_VIP/asureVIP_TVS_GPIO_OVM_VIP_PB.pdf
https://github.com/imokanj/gpio_agent/blob/master/doc/GPIO_Agent_User_Manual.pdf