I'd guess that one of the first stores banks in RAM or I/O or something at F800-FBFF at least. The read-discard-store pattern on F890 and F891 is suggestive of them being IRQ status/enable registers.

The rest of the code looks like bit 6 of F892 is possibly VBL status, and that VBL IRQ is enabled by bit 4 of F891.

F88D is probably a watchdog and system control (ie, banking).

Last edited by R. Belmont; 05/28/15 03:11 PM.