I bookmarked a few useful RAM offsets for reference when programming in ASM: $FFFFD080: Whenever you load an object you move the object number here. $C00004: Before moving Nemesis compressed art to a0, you always move something here. $FFFFF600: This offset is the offset that holds where you are in the Main Game Loop. $FFFFFFF8: This offset contains which machine the Genesis is. $FFFFFE10: This offset contains which level you're in. $FFFFFE11: This offset contains which act you're in. #FFFFFE20: This offset contains how many rings you have, $FFFFFE22: This offset contains the current time. $FFFFFE1B: This offset contains how many lives are in the lives counter. $FFFFFE2C: This offset contains the shield value (0 = False, 1 = True) $FFFFFE2D: This offset contains the invincibility value (0 = False, 1 = True) $FFFFFE1B: This offset contains how many rings are in the rings counter. $FFFFFE57: This offset contains how many emeralds you have. $FFFFD008: Sonic's X position $FFFFD00C: Sonic's Y position Not much, but hey.
Take a look at this text file (by QuickMan). http://pci.univ-lyon1.fr/~p0300958/RAM.txt It contains much more informations about that (even if some aren't in it).
Also, drx has stolen borrowed it in making his RAM breakdown page. I may as well note that a lot of that info is from Saxman's originals, with some other stuff from sources I've long since forgotten.
QM's does have lots more info, but only 4 of mine are listed in his. Oh yeah, and QM, $FE22.w contains the time, not some unknown mysterious variable. =P But this is just more proof that QM knows a lot more than I will ever do. I'm an idiot. >.<
:P Seriously though, I wasn't aware of that when I first wrote the document (being unaware of the nature of the CLOCK).