pub fn start_measurement(&mut self) {
        crate::peripherals::RTC_IO::regs()
            .touch_pad2()
            .write(|w| unsafe {
                w.start().set_bit();
                w.xpd().set_bit();
                // clear input_enable
                w.fun_ie().clear_bit();
                // Connect pin to analog / RTC module instead of standard GPIO
                w.mux_sel().set_bit();
                // Disable pull-up and pull-down resistors on the pin
                w.rue().clear_bit();
                w.rde().clear_bit();
                w.tie_opt().clear_bit();
                w.to_gpio().set_bit();
                // Select function "RTC function 1" (GPIO) for analog use
                w.fun_sel().bits(0b00)
            });

        crate::peripherals::SENS::regs()
            .sar_touch_ctrl2()
            .modify(|_, w| w.touch_start_en().clear_bit());
        crate::peripherals::SENS::regs()
            .sar_touch_ctrl2()
            .modify(|_, w| w.touch_start_en().set_bit());
    }
(Re-)Start a touch measurement on the pin. You can get the result by
calling [`read`](Self::read) once it is finished.
esp-hal/src/touch.rs