Actuating mechanism for a timepiece movement, in particular chronograph mechanism comprising such an actuating mechanism

An "all or nothing" actuating mechanism for a timepiece movement is described, which includes: an actuating lever that is able to move between an inactive position and an active position; a movable control lever for moving the actuating lever between its inactive and active positions; a return member for returning the control lever to its initial position; and a control member capable of pivoting between a first state in which it locks the actuating lever in its inactive position, and a second state, in which it releases the actuating lever to allow it to move to its active position. The control lever is arranged to be able to act on the control member, and move it from its first state to its second state, the actuating mechanism including a jumper tending to return the control member to its first state.