Rockbox

This patch is a proof-of-concept for an adaptive runtime estimation.

Reason to implement such behaviour is that different user settings and user behaviour have large impact to the power consumption and -- as a result -- to the runtime. E.g. disabling LCD will save lots of power, but some users do not want to disable the LCD to keep readability in daylight.
This patch therefor adapts the estimation of runcurrent() based upon real measurements of the current consumption. The algorithm starts with a default (CURRENT_NORMAL which is defined in the config-file of each player) and uses a weighting scheme with a large time constant to adapt the estimation of the current consumption. The time constant is 1024, which should equal ~20 minutes as the runcurrent()-function is called once per second. With a smaller time constant the runtime estimation is "pumping" too much when the HDD is active.

This first version is just a hard coded experimental solution. Nevertheless something like an actual_current()-function can be implemented for each player in its own powermgmt-file. Players with capability to read the current will return this measured real current, all others still return the fixed default CURRENT_NORMAL.