I found the rockbox alarm clock quite frustrating : once set, you have to stop using the D2 until the time set and leave it on, consuming battery life.
Then I stumbled on this :
1 > Mix rockbox sleep timer & D2 firmware alarm clock
1' > or just use D2 fw alarm clock
2 > make sure you don't stop rockbox on D2 in pause mode AND lock the hold button
3 > at the time set in D2 fw, rockbox will start & resume playback where it was.
Something similar might work on other ports, try it and let us know.
I think this is worth mentioning in the manual.
And by the way, I've been using rockbox on my D2 on a daily basis for over a year now, with various SDHC, micro SDHC cards and cannot report any but one single crash.
Although rockbox is not officially portable on D2s, I suggest to declare the D2 officially rockboxable !!