New release of the application StLinkP is published on GooglePlay.
New options "connect under reset" is added.
Some times debugger St-Lint can't connect to CPU while firmware is running.
It maybe by some reasons. For example firmware can use for some other purposes the pins which debugger use to connect to CPU.
Also fimware can switch microcontroller in some safe energy mode.
In such situations debugger can provoke reset of microcontroller and catch control over it before firmware is start.
In many situation the application StLink make this action automatically if it can't connect normally.
Now you can select option "Connection under reset" and the application will be try connect to microcontroller under reset at once.