Design a one-shot triggered by the CPU. Use a fast comparator (possibly built into the CPU) to reset the one-shot based on V=I*R3.Unless I misunderstand where you are going with this.
Edit: that was elaboration re the case including R3.
Design a one-shot triggered by the CPU. Use a fast comparator (possibly built into the CPU) to reset the one-shot based on V=I*R3.Unless I misunderstand where you are going with this.