A downhole tool for connecting an interior of a casing to a formation, the downhole tool including an inner housing extending along a longitudinal axis X; an outer housing that encloses the inner housing and forms first and second chambers; a piston that separates the first and second chambers; a port that fluidly communicates an outside and inside of the downhole tool; and a stopping mechanism that prevents the piston from opening the port. The piston interrupts the fluid communication between the outside and inside the downhole tool.