I will try to answer alexban's "one question"...
In case of a failure that will invalidate the speed data , for ex the pitot system blocked, what would happen if the speed slows too much?
In Normal Law there are two protections designed to prevent a stall - high AoA protection in which the FBW limits the a/c to αmax, and ALPHA FLOOR in which the A/THR provides TOGA thrust. With invalid speed data tha A320 switches to Alternate Law and these protections are no longer available. So if the a/c slows too much it will stall.
On a type rating course recovery is practised from the approach to the stall in clean config (alternate law) and landing config (direct law). The stall is completely conventional.
TP (A320 SFI)