Using the STM32 Nucleo L152RE with uVision
Turns out that the Nucleo likes to connect under reset, maybe something to do with the mbed bootloader. 

This can pretty easily be resolved by changing the settings of the st-link debugger in uVision to connect under reset.



On a side note, if you create a new project using STM32CubeMX, it also tends to set the port as 'JTAG' rather than 'SW'.