SYSTEM INT1

SYSTEM_INT1 ($C00438): Multi-purpose VBL call

Needs to be called at the beginning of the vblank period. Sets values in RAM according to buttons states, checks CDDA commands, calls MESS_OUT, and probably other things...

If called outside of vblank, interrupts need to be disabled before.

Memory locations set (all 8bit):

BIOS_P1CURRENT     ;$10FD95 Joystick 1 state
BIOS_P1PREVIOUS    ;$10FD96 Previous joystick 1 state
BIOS_P1CHANGE      ;$10FD97 Joystick 1 state change (edges)
BIOS_P1REPEAT      ;$10FD98 Joystick 1 repeat (edge, and strobe if held more than ? calls)

BIOS_P2CURRENT     ;$10FD9B Joystick 2 state
BIOS_P2PREVIOUS    ;$10FD9C Previous joystick 2 state
BIOS_P2CHANGE      ;$10FD9D Joystick 2 state change (edges)
BIOS_P2REPEAT      ;$10FD9E Joystick 2 repeat (edge, and strobe if held more than ? calls)

BIOS_STATCURNT     ;Joystick 1/2 start/select state
BIOS_STATCHANGE    ;Previous Joystick 1/2 start/select state

Bit definitions: see Joypad