I am working on Raspberry Pi 2 + GrovePi with Snappy Ubuntu Core (15.04), and I find the initial status of GPIO 15 (UART0 RX) is different after plugging GrovePi to RPi2.
I flash the the Ubuntu core to RPi2 and power on, the uboot counts down and auto boot into Ubuntu core normally,
but when I plug GrovePi to RPi2, the uboot stops autoboot and goes to prompt, but when I connect UART to my laptop, uboot becomes normally again (auto boot into Ubuntu) and UART works fine.
It looks uboot considers there is a key pressed from UART at the first power on when plugging GrovePi to RPi2 without UART connected,
so I try to measure the GPIO 15 / UART Rx and find that without GrovePi plugged, the initial status of GPIO 15 is high but when GrovePi plugged, the GPIO 15 initial status becomes low.
It leads to uboot stop autoboot, I also check the schematic GrovePi+_2.2_schem.pdf from https://github.com/DexterInd/GrovePi.git, it looks GPIO15,UART0_RXD is connected to RPI-RX directly,
Currently I just connect GPIO15 to a 5V pin, then it works fine but it doesn’t seem right, so I wonder why the initial status is changed or is there anything I can do without connect GPIO15 to a 5V pin?