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Mega Drive.asm
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Mega Drive.asm
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; ---------------------------------------------------------------------------
; Standard Mega Drive constants & macros
; ---------------------------------------------------------------------------
; VDP addressses
vdp_data_port: equ $C00000
vdp_control_port: equ $C00004
; Status register bits
video_mode_bit: equ 0 ; 0 if NTSC, 1 if PAL
dma_status_bit: equ 1 ; 1 if a DMA is in progress
hblank_bit: equ 2 ; 1 if HBlank is in progress
vblank_bit: equ 3 ; 1 if VBlank is in progress
interlaced_counter_bit: equ 4 ; 0 if even frame displayed in interlaced mode, 1 if odd
hardware_collision_bit: equ 5 ; 1 if any two sprites have non-transparent pixels overlapping
sprite_limit_bit: equ 6 ; 1 if sprite limit (16 in H32, 20 in H40) has been reached on current scanline
vertical_interrupt_bit: equ 7 ; 1 if a vertical interrupt has just occurred
fifo_full_bit: equ 8 ; 1 if VDP FIFO is full
fifo_empty_bit: equ 9 ; 1 if VDP FIFO is empty
; VDP register settings
vdp_mode_register1: equ $8000
vdp_left_border: equ vdp_mode_register1+$20 ; blank leftmost 8px to bg colour
vdp_enable_hint: equ vdp_mode_register1+$10 ; enable horizontal interrupts
vdp_md_color: equ vdp_mode_register1+4 ; Mega Drive colour mode
vdp_freeze_hvcounter: equ vdp_mode_register1+2 ; freeze H/V counter on interrupts
vdp_disable_display: equ vdp_mode_register1+1
vdp_mode_register2: equ $8100
vdp_128kb_vram: equ vdp_mode_register2+$80 ; use 128kB of VRAM, Teradrive only
vdp_enable_display: equ vdp_mode_register2+$40 ; enable display
vdp_enable_vint: equ vdp_mode_register2+$20 ; enable vertical interrupts
vdp_enable_dma: equ vdp_mode_register2+$10 ; enable DMA operations
vdp_pal_display: equ vdp_mode_register2+8 ; 240px screen height (PAL)
vdp_ntsc_display: equ vdp_mode_register2 ; 224px screen height (NTSC)
vdp_md_display: equ vdp_mode_register2+4 ; mode 5 Mega Drive display
vdp_fg_nametable: equ $8200 ; fg (plane A) nametable setting
vdp_window_nametable: equ $8300 ; window nametable setting
vdp_bg_nametable: equ $8400 ; bg (plane B) nametable setting
vdp_sprite_table: equ $8500 ; sprite table setting
vdp_sprite_table2: equ $8600 ; sprite table setting for 128kB VRAM
vdp_bg_color: equ $8700 ; bg colour id (+0..$3F)
vdp_sms_hscroll: equ $8800
vdp_sms_vscroll: equ $8900
vdp_hint_counter: equ $8A00 ; number of lines between horizontal interrupts
vdp_mode_register3: equ $8B00
vdp_enable_xint: equ vdp_mode_register3+8 ; enable external interrupts
vdp_16px_vscroll: equ vdp_mode_register3+4 ; 16px column vertical scroll mode
vdp_full_vscroll: equ vdp_mode_register3 ; full screen vertical scroll mode
vdp_1px_hscroll: equ vdp_mode_register3+3 ; 1px row horizontal scroll mode
vdp_8px_hscroll: equ vdp_mode_register3+2 ; 8px row horizontal scroll mode
vdp_full_hscroll: equ vdp_mode_register3 ; full screen horizontal scroll mode
vdp_mode_register4: equ $8C00
vdp_320px_screen_width: equ vdp_mode_register4+$81 ; 320px wide screen mode
vdp_256px_screen_width: equ vdp_mode_register4 ; 256px wide screen mode
vdp_shadow_highlight: equ vdp_mode_register4+8 ; enable shadow/highlight mode
vdp_interlace: equ vdp_mode_register4+2 ; enable interlace mode
vdp_interlace_x2: equ vdp_mode_register4+6 ; enable double height interlace mode (e.g. Sonic 2 two player game)
vdp_hscroll_table: equ $8D00 ; horizontal scroll table setting
vdp_nametable_hi: equ $8E00 ; high bits of fg/bg nametable settings for 128kB VRAM
vdp_auto_inc: equ $8F00 ; value added to VDP address after each write
vdp_plane_size: equ $9000 ; fg/bg plane dimensions
vdp_plane_height_128: equ vdp_plane_size+$30 ; height = 128 cells (1024px)
vdp_plane_height_64: equ vdp_plane_size+$10 ; height = 64 cells (512px)
vdp_plane_height_32: equ vdp_plane_size ; height = 32 cells (256px)
vdp_plane_width_128: equ vdp_plane_size+3 ; width = 128 cells (1024px)
vdp_plane_width_64: equ vdp_plane_size+1 ; width = 64 cells (512px)
vdp_plane_width_32: equ vdp_plane_size ; width = 32 cells (256px)
vdp_window_x_pos: equ $9100
vdp_window_right: equ vdp_window_x_pos+$80 ; draw window from x pos to right edge of screen
vdp_window_left: equ vdp_window_x_pos ; draw window from x pos to left edge of screen
vdp_window_y_pos: equ $9200
vdp_window_bottom: equ vdp_window_y_pos+$80 ; draw window from y pos to bottom edge of screen
vdp_window_top: equ vdp_window_y_pos ; draw window from y pos to top edge of screen
vdp_dma_length_low: equ $9300
vdp_dma_length_hi: equ $9400
vdp_dma_source_low: equ $9500
vdp_dma_source_mid: equ $9600
vdp_dma_source_hi: equ $9700
vdp_dma_68k_copy: equ vdp_dma_source_hi ; DMA 68k to VRAM copy mode
vdp_dma_vram_fill: equ vdp_dma_source_hi+$80 ; DMA VRAM fill mode
vdp_dma_vram_copy: equ vdp_dma_source_hi+$C0 ; DMA VRAM to VRAM copy mode
vdp_counter: equ $C00008
psg_input: equ $C00011
debug_reg: equ $C0001C
; Z80 addresses
z80_ram: equ $A00000 ; start of Z80 RAM
z80_dac3_pitch: equ $A000EA
z80_dac_status: equ $A01FFD
z80_dac_sample: equ $A01FFF
z80_ram_end: equ $A02000 ; end of non-reserved Z80 RAM
ym2612_a0: equ $A04000
ym2612_d0: equ $A04001
ym2612_a1: equ $A04002
ym2612_d1: equ $A04003
z80_bank_reg: equ $A06000 ; Bank register for address $8000-$FFFF
z80_psg: equ $A07F11
; I/O addresses
console_version: equ $A10001
console_region_bit: equ 7 ; 0 = Japan; 1 = overseas
console_speed_bit: equ 6 ; 0 = NTSC; 1 = PAL
console_mcd_bit: equ 5 ; 1 = Mega-CD attached (or other addon?)
console_region: equ 1<<console_region_bit
console_speed: equ 1<<console_speed_bit
console_mcd: equ 1<<console_mcd_bit
console_revision: equ $F ; revision id in bits 0-3; revision 0 has no TMSS
port_1_data_hi: equ $A10002
port_1_data: equ $A10003
port_2_data_hi: equ $A10004
port_2_data: equ $A10005
port_e_data_hi: equ $A10006
port_e_data: equ $A10007
port_1_control_hi: equ $A10008
port_1_control: equ $A10009
port_2_control_hi: equ $A1000A
port_2_control: equ $A1000B
port_e_control_hi: equ $A1000C
port_e_control: equ $A1000D
; Z80 addresses
z80_bus_request: equ $A11100
z80_reset: equ $A11200
; Bank registers, et al
sram_access_reg: equ $A130F1
bank_reg_1: equ $A130F3 ; Bank register for address $80000-$FFFFF
bank_reg_2: equ $A130F5 ; Bank register for address $100000-$17FFFF
bank_reg_3: equ $A130F7 ; Bank register for address $180000-$1FFFFF
bank_reg_4: equ $A130F9 ; Bank register for address $200000-$27FFFF
bank_reg_5: equ $A130FB ; Bank register for address $280000-$2FFFFF
bank_reg_6: equ $A130FD ; Bank register for address $300000-$37FFFF
bank_reg_7: equ $A130FF ; Bank register for address $380000-$3FFFFF
tmss_sega: equ $A14000 ; contains the string "SEGA"
tmss_reg: equ $A14101
; Memory sizes
sizeof_ram: equ $10000
sizeof_vram: equ $10000
sizeof_vsram: equ $50
sizeof_z80_ram: equ z80_ram_end-z80_ram ; $2000
sizeof_z80_bank: equ $8000 ; size of switchable Z80 ROM window
; ---------------------------------------------------------------------------
; stop the Z80
; ---------------------------------------------------------------------------
stopZ80: macros
move.w #$100,(z80_bus_request).l
; ---------------------------------------------------------------------------
; wait for Z80 to stop
; ---------------------------------------------------------------------------
waitZ80: macro
.wait\@:
btst #0,(z80_bus_request).l
bne.s .wait\@
endm
; ---------------------------------------------------------------------------
; start the Z80
; ---------------------------------------------------------------------------
startZ80: macros
move.w #0,(z80_bus_request).l
; ---------------------------------------------------------------------------
; reset the Z80
; ---------------------------------------------------------------------------
resetZ80_assert: macros
move.w #0,(z80_reset).l
resetZ80_release: macros
move.w #$100,(z80_reset).l
; ---------------------------------------------------------------------------
; disable interrupts
; ---------------------------------------------------------------------------
disable_ints: macros
move #$2700,sr
; ---------------------------------------------------------------------------
; enable interrupts
; ---------------------------------------------------------------------------
enable_ints: macros
move #$2300,sr
; ---------------------------------------------------------------------------
; bankswitch between SRAM and ROM
; (remember to enable SRAM in the header first!)
; ---------------------------------------------------------------------------
gotoSRAM: macros
move.b #1,(sram_access_reg).l
gotoROM: macros
move.b #0,(sram_access_reg).l