SYSTEM INT1

BIOSF_VBL ($C0044A): Multiple purpose VBL routine
Sets values in RAM according to buttons states, checks CDDA commands, probably other things... Always (?) called each frame by games.

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