pub fn timestamp(&self) -> u16 {
        // SAFETY:
        // We only read to our GENx_TSTMP_x register
        let ch = unsafe { Self::ch() };

        #[cfg(esp32s3)]
        if IS_A {
            ch.cmpr_value0().read().a().bits()
        } else {
            ch.cmpr_value1().read().b().bits()
        }

        #[cfg(any(esp32, esp32c6, esp32h2))]
        if IS_A {
            ch.gen_tstmp_a().read().a().bits()
        } else {
            ch.gen_tstmp_b().read().b().bits()
        }
    }
Get the old timestamp.
The value of the timestamp will take effect according to the set
[`PwmUpdateMethod`].
esp-hal/src/mcpwm/operator.rs