I'm trying to figure a circuit design that when it is powered it outputs high. Then, when it get a pulse as input (low or high, I don't mind) it wait some time and then put the output to low.
The reason is I have a board with a processor running Linux . If Linux halting process finishes OK, power is cut with no problem, but what happens when halting never finish?
What I'm thinking is starting a timing with a pulse generated by one GPIO before starting Linux halt, and when this timing finish, power is cut even if halting hasn't completed yet. When Linux halt starts, I can't control GPIOs anymore, so I can't maintain certain voltage level in the GPIO pin, that's why I say I need to start timing with a pulse.
I've tried to figure a circuit using 555 timer, but it outputs high during the timing, but not before starting timing.