"remaining headroom" display for recording screen

[ulmutul]

Hello, since I'm new to the whole rockboxing thing, I've some questions.

The described feature is something I want to have (to be more precise: I want to share because it already runs fine on my target/Vibe500), because when recording it's good to not only rely on a peakmeter, but to see the maximum recorded level as an precise value. This makes it easier to level out external equipment or to choose the best gain level of your DAP.
However it's only useful if you have the possibility to manually reset the displayed value.
Besides I redefined "max level" to "remaining headroom" to safe the space for the leading negative sign in dB scale.

What I've done is using the same space as the clipcounter on the recording screen. I added a menu entry for the headroom display. Currently you can activate Headroom display and Clipcounter individually. If both are selected, it works as following: headroom is displayed as long as the clipcounter is 0, otherwise the number of clips are displayed. (BTW I noticed a strange behaviour of the clipcounter: it seems to count at a level far beyond the peakmeter reports clipping... I have to investigate this further)

Now these are my questions:

• is there any more generic way to convert PCM values to dBfs than calc_db() located in peakmeter.c?
• I picked some random targets and added the "reset headroom" to the buttonmap, but some targets are very limited in buttons. Some targets even have no button defined for the recording submenu! Who takes care of a logical and consistent mapping? Do I have to add buttons to all targets?
• PLEASE DISCUSS: should the clipcounter also be manually resettable? Currently headroom and clipcounter is resetted automatically when a (new) file is opened, but if you reset the headroom by hand, there will still be the clips displayed (if any occurred).
• PLEASE DISCUSS: for my taste two separate menu entries seems a bit bloated; you can't have both headroom and clipping at the same time, right? So I would be totally happy with a single "Show headroom & clips" menu entry with the above described "both ON" behaviour (display headroom as long as there is no clipping, clipcounter otherwise). Should I remove the clipcounter menu entry?