Unclarity on Sati-Sampajañña

In one Sutta the Buddha said that one should constantly be mindful of the fact of anicca. In the Satipatthana Sutta he said that when one is dressing, eating, speaking etc. one should be aware that he is doing exactly that. Now my two questions (and yes I know that Sati is more than just present moment awareness in that it can also mean remembering something or calling somethibg helpful to mind) 1. The aspect of knowing what one is doing is connected with mental noting, right? Because the Buddha never (correct me if Im wrong) mentioned to note something as seeing, seeing, touching, touching.. etc. 2. If I am not mistaken the Buddha said one should constantly dwell/remind oneself of the fact of anicca but at the same time one should know what one is doing. This is confusing. When does one know when to use "what one is doing-mindfulness" and when to dwell on "impermanence-mindfulness"? 3. Is continous present moment awareness actually endorsed by the Buddha? Kind of confusing because first of one cannot be mindful all the time and secondly, how is one able to be present aware if one uses sati in the "remembering" sense when for example a hindrance is present? I think that the word "constant" or "continous" is just a word that puts strong emphasize on a specific activity, but I might be wrong.