GPIO state is reset by SoftReset (Migrating SDK 13 -- 15)

Question

Hi. 
 My target board has a power switch that is managed by GPIO. 
 First-time, a user clicks the button, the GPIO is turned on and the system wakes up. 
 In reset case(Firmware updates or assertion failure), the GPIO state is also maintained so the system can operate normally. 
 When I use SDK-13 & SoftDevice(v 4.x), above scenario goes well. 
 Now we are migrating to SDK-15 & SoftDevice (v 6.0). 
 But after Soft-reset(NVIC_SystemReset) the GPIO state is reset to zero and the system goes to the power-off state. 
 Is there any way to maintain GPIO state after Soft-reset using SoftDevice (v. 6) 
 Best.

paul_tanner · Answer

I have the same issue, not as a result of migration but anyway. I needed a logic low to disable the other modules on my board. When the GPIO floats (as seems to be the case during reset) the other modules are not disabled. This means that the full potential power saving is not achieved. 
 I think I need to change this by inserting a pullup and an inverter so that GPIO high *or float* will disable the other modules. I suspect that the internal pullup on the GPIO would not be effective because that is also disabled during reset. An easier fix may be the pull down the GPIO. I'll try that first.

GPIO state is reset by SoftReset (Migrating SDK 13 --> 15)