We know a micro can be powered up using its GPIO. If you didn't know - Link
I have an STM32F0103 which will be in OFF state (VCC = 0 V) and another uC which will be connected to it through SPI. The second uC can initiate an SPI transaction - call chip select, send SCK etc, but the STM is still in its OFF state. So my question is
1.Will this cause the STM to get powered for a brief duration (when the pin is high)? I know it won't get enough current (the second uC GPIO pin won't supply enough), but will this flickering power cycle cause problems?
2.What should I do to prevent this if it happens?
The application implementation seems risky reliability speaking.
The unpowered GPIOs might degrade the transiting SPI device signals.
True open dain "power fail safe" SDA/SCL pins of an I2C bus mode would be better suited at lower bitrate.
Otherwise maybe adding cheap serial resistors on the SPI lines going to the unpowered SPI device to minimize issues?