I've been trying to figure out for a while why dircache fails to work on my H120 seemingly at random. Today I stumbled upon what's going on.
If the unit is turned on using battery power, and then the power cord is plugged in while the rockbox title screen is being displayed, for whatever reason the dircache thread does not start (or is interrupted or something). The filebrowser then behaves as if dircache is disabled. This is 100% reproducible (using cvs build as of today). bk
