Ok, here a short description why the source code is universal. It can be assembled and run on the X68000 and with only a few lines changed with additional TRAP and LINEF handlers the same source runs on a Atari ST as well (without any graphics emulation).
Addresses for interrupt vectors and X68000 memory mapped adresses are defined as follows (Pac-Mania):
Code:
move.l L_0000007C,OLD_7C_HANDLER.l
move.l #NULL_NMI_HANDLER,L_0000007C
move.l L_000000AC,OLD_AC_HANDLER.l
move.l #NULL_IRQ_HANDLER,L_000000AC
move.l L_000000B0,OLD_B0_HANDLER.l
move.l #NULL_IRQ_HANDLER,L_000000B0
move.l L_000000B4,OLD_B4_HANDLER.l
move.l #NULL_IRQ_HANDLER,L_000000B4
move.l L_000000B8,OLD_PROGRAM_ERROR_HANDLER.l
move.l #PROGRAM_ERROR_HANDLER,L_000000B8
The example above shows the interrupt vectors initialisation. The X68000 source has simply the label definitions like this: "L_0000007C = 0x0000007c" where the Atari source has the label pointing to a long word within the BSS area.
The VBL handling would look like this:
Code:
vbl:
[Your code]
move.l L_00000118,-(sp)
beq.s _vbl_no_vdisp_handler
rts
_vbl_no_vdisp_handler:
addq.l #4,sp
rte
Here the handling of memory mapped registers: the X68000 target has the label defined as being described above where the Atari source defines a buffer within the BSS area:
Code:
move.w L_00E80000+0x2A.l,OLD_CRTC_PLANE_ACCESS_MODE_REGISTER.l
move.w #0x0,L_00E80000+0x2A.l
move.w L_00E82000+0x500.l,OLD_VIDEO_CONTROLLER_PRIORITY_REGISTER.l
move.w #0x12E4,L_00E82000+0x500.l
move.w L_00E82000+0x600.l,OLD_VIDEO_CONTROLLER_SPECIAL_PRIORITY_REGISTER.l
move.w #0x0,L_00E82000+0x600.l
move.w L_00EB0000+0x808.l,OLD_BG_CONTROL_REGISTER.l
move.w #0x212,L_00EB0000+0x808.l
Code:
L_00E80000: | CRTC
ds.b 0x2000
L_00E82000: | VIDEO CONTROLLER
ds.b 0x2000
L_00EB0000: | SPRITE REGISTERS
ds.b 0x8000
All you now need to do is to read the X68000 registers from the BSS area and emulate it.
