; ***************************************************************************** ; ***************************************************************************** ; ; Nintendo Entertainment System in Assembler (NESA) ; ================================================= ; ; 0.00 06-Sep-96 Started work on main body of the emulator ; 07-Sep-96 Writing to PPU Memory,Sprite Memory and Registers ; Got millipede title screen up ! this is great ! ; 08-Sep-96 Got 'Popeye','Circus' and 'Millepede' title screens ; up,fixed an irritating bug in NESA. ; 09-Sep-96 Did a little bit of work on NESA (Read from PPU Memory) ; Got Mario 1 screen up. ; 10-Sep-96 Horizontal Scroll now works ok. Wrote sprite code ; Wrote Joystick Code. ; 0.10 I CAN PLAY SUPER MARIO !!!!!! ; 0.11 11-Sep-96 Fixed interrupt bug (Z register update !) ; Fixed bug (fetch bl meant code in RAM didn't work) ; 0.12 Did 8 x 16 sprites according to NES Architecture doc. ; Did Background sprites ; Had a go at the split screen code. ; Z Key as alternative to Left Alt (probs under Windows) ; Line Table -T switch ; Added support for type 3 cartridges ; 0.13 Moved code pointers out of iNES file into a space ; which is copied to. ; Can write to VRAM (reqd. No VROM Banks) ; Added battery back-up RAM (not loaded/saved !) ; Added support for type 1/2 cartridges. ; Added scroll scan line override. ; 0.14 Added toggle mirror switch. ; 0.15 Screen mask count can be any value ; All sprites down one line ! ; Added support for the HIT flag ; 0.16 Fixed the colour palette ; 0.17 Tweaked VGA mode ; ; Battle City Problems... Writing $C0 to $4017 ; ; ***************************************************************************** ; ***************************************************************************** LineSize equ 256 ; bytes per VGA display line ScrHeight equ 224 jmp start org 120h ; for joysticks.... dw 0,0,0,0 db 'NESJoyCal' even ; ***************************************************************************** D_TraceCPU equ 0 ; if 1 trace the CPU D_TraceRW equ 0 ; if 1 trace W to PPU Ram D_TraceReg equ 0 ; if 1 trace Registers D_TracePalette equ 0 ; if 1 trace palette D_Debugger equ 0 ; if 1 remove gfx/int for debugger D_Fast equ 0 ; if 1 go fast CHorzScan: dw 90 ; CPU Cycles/Horizontal Scan (visible) CHorzBlank: dw 10 ; CPU Cycles/Horizontal Scan (blank) StartScan: dw 8 ; Scan line where screen starts EndScan: dw 232 ; Scan line where screen ends EndScreen: dw 262 ; Scan line,end of screen ScanLine: dw 0 ; Current Scanline ScrDrawMask: dw 3 ; Screen draw mask NoSplit: dw 0 ; if 1 no split screen. PPUCtrl1: db 0 ; PPU Control Register 1 (R/W) PPUCtrl2: db 0 ; PPU Control Register 2 (R/W) PPUStatus: db 0 ; PPU Status (Read Only) PPUSpriteAddr: db 0 ; Sprite Memory Address PPUVScroll: db 0 ; Vertical Scroll PPUHScroll: db 0 ; Horizontal Scroll PPUMemoryAddr: dw 0 ; PPU Memory Address _HMirror: db 0 ; 1 if horiz mirror,0 if vert mirror MToggle: db 0 ; mirror toggle. NESPalette: db 32 dup 0 ; NES Palette Registers (3f00-3f1f) LineTable: dw LineAddress ; Line table CartType: db 0 ; cartridge type OverRide: db 0 ; line to override scroll pos at VSSegment: dw 0 ; Virtual Screen Segment ESSegment: dw 0 ; 64k code space ; ***************************************************************************** MSDOS = 33 ; MSDOS Function Number start: mov sp,Stack86+StackSize-2 ; initialise the 8086 stack. call ClearRAM #if D_Debugger=0 call ShowGraphic #if LineSize=256 call TweakVideo #endif call SetNewInt9 call WrBanner #endif mov ax,cs ; Calculate where VScreen goes add ax,256 * 1024 / 16 ; well out of the way ! mov [VSSegment],ax add ax,68*1024/16 mov [ESSegment],ax ; code space call ClearVS call Initialise CPUReset main1: call Clock ; read and save CPU Clock push ax call DoScreen ; do three screens call DoScreen call DoScreen pop bx #if D_Fast=0 wait1: call Clock ; wait until clock changed cmp ax,bx ; frame rate about 55fps je wait1 #endif mov al,[KeyTable+1] cmp al,0 jz main1 call ShowText jmp DExit ; ***************************************************************************** ; ; Do one CPU Screen ; ; ***************************************************************************** _TopSection:db 0 ; top of current section OldScroll: dw 0 ; previous VScroll/HScroll value DoScreen: mov ax,word [_ScrCount] ; decrement screen mask count cmp ax,0 ; if its zero,reset the counter. jnz _NoScrC1 mov ax,[ScrDrawMask] _NoScrC1: dec ax mov word [_ScrCount],ax mov word [ScanLine],0 ; back to the top of the screen mov si,0 ; reset the cycle counter to zero TopVBlank: mov ax,[StartScan] ; do the top few scanlines. cmp ax,[ScanLine] je CompletedTopVBlank call DoScanLine ; do a scanline jmp TopVBlank CompletedTopVBlank: mov al,[ScanLine] mov [_TopSection],al and byte [PPUStatus],63 ; reset the vblank+hblank flag VisibleScreen: mov ax,[PPUVScroll] ; save scroll registers mov [OldScroll],ax call DoScanLine ; do the visible screen mov ax,[NoSplit] cmp ax,0 jne VSNoChange mov ax,[OldScroll] cmp ax,[PPUVScroll] ; reload scroll registers je VSNoChange ; if changed push cx mov ax,[PPUVScroll] push ax mov ax,[OldScroll] mov [PPUVScroll],ax mov cl,[_TopSection] mov ch,[ScanLine] add ch,8 test byte [OverRide],255 jz NoOvr mov ch,[OverRide] NoOvr: mov [_TopSection],ch dec ch call Screen pop ax mov [PPUVScroll],ax pop cx VSNoChange: mov ax,[ScanLine] cmp ax,[EndScan] jne VisibleScreen push cx mov cl,[_TopSection] mov ch,[EndScan] call Screen ; redraw the screen pop cx or byte [PPUStatus],128 ; set the vblank flag on. test byte [PPUCtrl1],128 ; if interrupt enabled jz BottomVBlank CPUNMI ; do it ! BottomVBlank: call DoScanLine ; do the bottom scanlines mov ax,[ScanLine] cmp ax,[EndScreen] jl BottomVBlank ret ExecuteDiCycles macro ; do at least Di Cycles add di,si M1: call Execute #if D_TraceCPU=1 cmp bp,08C31h jne >M3 mov byte [_Trace],1 M3: test byte [_Trace],255 jz >M2 call Dump M2: #endif cmp si,di jb M1 #em _Trace: db 0 DoScanLine: ; do a scan line (in VBlank) mov ax,[ScanLine] ; does scanline = Sprite 0 ???? mov di,SpriteRAM cmp al,[di] jne _DSL1 or byte [PPUStatus],64 ; set the hit bit _DSL1: mov di,[CHorzScan] ; do HorzScan+HorzBlank cycles add di,[CHorzBlank] ; not strictly necessary now ! ExecuteDiCycles inc word [ScanLine] ret ; ***************************************************************************** ; ; Return to MSDOS ; ; ***************************************************************************** DExit: #if D_Debugger=0 call SetOldInt9 #endif mov ah,04Ch int MSDOS ; ***************************************************************************** ; ; Read file (name at ds:bx) into Memory ; ; ***************************************************************************** LoadROM: push ax,bx,cx,dx,es,ds mov dx,bx ; open the file. mov al,0 mov ah,03Dh int MSDOS jc LoadFail push ax ; save handle for close mov bx,ax ; read the file bx = handle mov ax,cs ; es = NESHeader add ax,NESHeader/16 mov ds,ax _LDLoop: xor dx,dx ; load to ES:0 mov cx,8192 ; bytes to read. mov ah,03Fh int MSDOS cmp ax,8192 jne _ELoad mov ax,ds add ax,8192/16 mov ds,ax jmp _LdLoop _ELoad: pop bx ; Close the file mov ah,03Eh int MSDOS pop ds,es,dx,cx,bx,ax ret LoadFail: mov al,7 call ConOut call ShowText jmp DExit ; ***************************************************************************** ; ; Copy 8k from ROMBank + AX * 1024 into VRAM Workspace ; ; ***************************************************************************** CopyVROM: push ds,es,si,di,cx,bx,ax mov di,VRom ; es:di points to the VROM space mov es,ds mov bx,cs ; ROMBank segment in DS now. add bx,(ROMBank/16) shl ax,10 - 4 ; left 10 (k# -> addr) right 4 (to seg) add bx,ax mov ds,bx mov si,0 ; ds:si now points to the VROM to copy mov cx,8192/2 ; no of words to copy (4k) rep movsw ; and copy it pop ax,bx,cx,di,si,es,ds ret ; ***************************************************************************** ; ; Copy 16k from ROMBank BX to CPU WorkSpace @ AX ; ; ***************************************************************************** CopyROM: push ds,es,si,di,cx,bx,ax mov di,ax ; es:di points to CPU target space mov es,[ESSegment] shl bx,(14-4) ; convert ROM# to segment mov ax,cs ; ROMBank segment in DS now. add ax,(ROMBank/16) add ax,bx mov ds,ax mov si,0 ; ds:si now points to the VROM to copy mov cx,16384/2 ; no of words to copy (16k) rep movsw ; and copy it pop ax,bx,cx,di,si,es,ds ret ; ***************************************************************************** ; ; Clear NESRam -> NESHeader ; ; ***************************************************************************** ClearRAM: push ax,bx mov bx,NESRam xor ax,ax CLR1: mov [bx],ax inc bx inc bx cmp bx,NESHeader jb CLR1 pop bx,ax ret ; ***************************************************************************** ; ***************************************************************************** ; ; Alternative INT9 Handler,allows us to check keyboard state. ; ; ***************************************************************************** ; ***************************************************************************** KeyTable:db 128 dup 0 ; Key pressed table OldInt9:dw 0,0 ; old vector for int9 SetNewInt9: push es,si,bx,ax cli mov ax,3509h ; get old INT 9 int 21h mov si,oldint9 mov [OldInt9],bx ; save offset mov [OldInt9+2],es ; save segment mov ax,2509h ; set new INT 9 mov dx,NewInt9 ; ds:dx new interrupt vector int 21h sti pop ax,bx,si,es ret SetOldInt9: push ds cli mov ax,2509h ; set new INT 9 mov dx,[OldInt9] ; load offset mov ds,[OldInt9+2] ; load segment int 21h sti pop ds ret NewInt9:push ax,bx in al,60h ; get the scan code mov bl,al ; bx = offset into the table and bl,07Fh xor bh,bh and al,080h ; isolate the on off bit xor al,080h ; bit 7 0 if key pressed,reverse it mov cs:KeyTable[bx],al ; write it into the table mov al,20h ; reset something or other.... out 20h,al ; (bit 7 set if pressed) pop bx,ax sti iret ; ***************************************************************************** ; ; Initialisation ; ; ***************************************************************************** Initialise: mov bx,081h ; Make Command Line ASCIIZ String INext: mov al,[bx] inc bx cmp al,32 je INext cmp al,'-' ; is it -???? je InitCtrl dec bx push bx Init1: mov al,[bx] cmp al,32 jbe Init2 inc bx jmp Init1 Init2: mov byte [bx],00 pop bx call LoadROM mov al,[NESHeader+6] ; get the cartridge type shr al,4 and al,15 mov [CartType],al cmp al,1 ; type 1 and 2 load last page into je _ZeldaCart ; $C000 and page 0 into $8000 cmp al,2 je _ZeldaCart cmp byte [NESHeader+4],1 ; if 2 16k ROM banks jne Is32kROM mov ax,16 ; copy VROM @ 16k call CopyVROM ; space mov ax,0C000h ; copy Bank 0 to C000h mov bx,0 call CopyROM mov ax,[ESSegment] jmp LoadCont Is32kROM: mov ax,32 ; copy VROM @ 32k call CopyVROM mov ax,08000h mov bx,0 call CopyROM mov ax,0C000h mov bx,1 call CopyRom mov ax,[ESSegment] LoadCont: mov es,ax ; set the register mov al,[NESHeader+6] and al,1 xor al,1 xor al,[MToggle] mov [_HMirror],al _Init1: ret InitCtrl: ; - mov al,[bx] cmp al,'a' ; convert to lower case jb InNotLC cmp al,'z' ja InNotLC sub al,32 InNotLC:xor cx,cx ; strip out the number inc bx InInt: mov dl,[bx] inc bx cmp dl,'0' jb InInt2 cmp dl,'9' ja InInt2 push ax ; multiply cx by 10 add cx,cx mov ax,cx shl cx,2 add cx,ax pop ax and dx,15 add cx,dx jmp InInt _ZeldaCart: ; load a zelda type cart mov ax,0C000h ; load last ROM Page to $C000 mov bl,[NESHeader+4] ; bx = last page # xor bh,bh dec bx ; pages numbered 0 .. n-1 call CopyRom mov ax,08000h ; load page 0 to $8000 xor bx,bx call CopyRom mov ax,[ESSegment] jmp LoadCont InInt2: ; al = command cx = integer cmp al,'H' je ISetHVis cmp al,'B' je ISetHBlk cmp al,'E' je ISetEScrn cmp al,'M' je ISetSMask cmp al,'S' je ISetNoSplit cmp al,'T' je AltLineAddress cmp al,'O' je SLOverride cmp al,'Q' je SetMToggle jmp INext SetMToggle: mov byte [MToggle],1 jmp INext SLOverRide: mov [OverRide],cl jmp INext ISetNoSplit: mov word [NoSplit],-1 jmp INext ISetHVis: mov [CHorzScan],cx jmp INext ISetHBlk: mov [CHorzBlank],cx jmp INext ISetEScrn: mov [EndScreen],cx jmp INext ISetSMask: mov [ScrDrawMask],cx jmp INext AltLineAddress: push ax,bx,cx,dx,si mov dx,256 ; lines to generate mov si,LineGenTable ; pointer mov [LineTable],si Alt1: cmp cx,0 ; while cx > 0 jz Alt2 mov word [si],0 ; generate 00 lines. add si,2 dec cx jmp Alt1 Alt2: mov bx,32 mov cx,200 Alt3: mov word [si],bx add bx,LineSize add si,2 dec cx jnz Alt3 Alt4: mov word [si],0 add si,2 cmp si,LineGenTable+512 jb Alt4 pop si,dx,cx,bx,ax jmp INext ; ***************************************************************************** ; ; Read DOS Clock ; ; ***************************************************************************** Clock: push bx,cx,dx mov ah,0 ; look at the clock tick int 01Ah mov ax,dx pop dx,cx,bx ret StackF0: push ax,bx mov bx,01F0h S1: mov al,NESRam[bx] call ConHex mov al,32 call ConOut inc bx cmp bx,0200h jne S1 mov al,13 call ConOut pop bx,ax ret ; ***************************************************************************** ; ; New VGA Banner ; ; ***************************************************************************** WrBanner: push ax,bx,si,di,es mov es,0A000h mov bx,LineSize-1 mov di,LineSize*ScrHeight-1 mov al,14 W1: mov es:[bx],al mov es:[di],al dec di dec bx jns W1 mov bx,(ScrHeight-1)*LineSize W2: mov es:[bx],al mov es:LineSize-1[bx],al sub bx,LineSize jnz W2 mov bx,(ScrHeight/2 - 46)*LineSize+(LineSize/2)-84 mov di,bx mov si,Banner WrBanner1: mov al,[si] call VGAChar inc si mov al,[si] cmp al,-2 jne WrBanner1 WrWait1:test byte [KeyTable+039h],128 jz WrWait1 WrWait2:test byte [KeyTable+039h],128 jnz WrWait2 xor bx,bx mov ax,bx WrClr: mov es:[bx],ax dec bx dec bx jnz WrClr pop es,di,si,bx,ax ret Banner: db ' nesa v0.17 (beta version)',-1,-1 db 'nintendo entertainment system in assembler',-1,-1 db ' written by paul robson [c] 1996',-1,-1 db ' dedicated to jane and elizabeth',-1,-1, db ' thanks to everyone who has contributed',-1,-1 db ' especially marat fayzullin ',-1,-1,-1 db ' press [space] to start',-2 VGAChar:test al,128 jnz VGANL push ax,cx,dx,si,di push bx mov si,0 VGAFind:mov ah,ChTable[si] cmp al,ah je VGAFound inc si cmp ah,0 jnz VGAFind jmp VCNext VGAFound: add si,si mov cl,5 mov ax,ChData[si] VGADraw:test ax,04000h jz VS1 mov byte es:[bx],11 VS1: test ax,02000h jz VS2 mov byte es:1[bx],11 VS2: test ax,01000h jz VS3 mov byte es:2[bx],11 VS3: shl ax,3 add bx,LineSize dec cl jnz VGADraw VCNext: pop bx add bx,4 VCExit: pop di,si,dx,cx,ax ret VGANL: add di,LineSize*6 mov bx,di ret