USER subroutine

The USER subroutine (not called, always jumped to by the BIOS) is required 68k code which needs to perform actions according to the command value set in.

At the end of the routine, a jump to BIOSF_SYSTEM_RETURN is needed to give back control to the BIOS.

=Handling code=

=USER_REQUEST values=

Command 0
Initilization of the soft/debug DIPs in the 68k user RAM. Used only once, when the game is started for the first time on a MVS system (probably when the BIOS doesn't find the game's NGH number in the backup RAM).

Set to 0 during operations, and don't forget to kick the watchdog as interrupts are disabled.

Initilization of the rest of the user RAM, the display, and I/O.

Viewpoint, which has its backup RAM save pointer set to $100000 (header $10E) and game save size set to $0200 (header $112) does this:

Typical use is load default data (default rankings, etc) into work-backup area, then jump to SYSTEM_RETURN.

Command 1
Show the game's own boot logo animation (when $114 = 1).

More information needed (end flag, BIOS_USER_MODE value ?).

Command 2
Show the game's demo (the recommended duration is ?).

Command 3
Show the game's title screen. This is called when a coin is inserted on MVS systems. is used as a count-down timer for auto-start.