;from caker137
;BASED ON MY HACK OF THE UPR ROMS AVAILABLE ONLINE
;read that first if you are trying to learn to hack romsets
;Discs of Tron 2-player Environmental Hack
;This hack is designed to work on the latest UPRIGHT romset
;released for DOT dated 10/83. They will work equally well
;in an Upright or Environmental cabinet.
;testing of ENV/UPR mode jumper is performed
;at address 0x20 for almost all game operations.
;this routine is called often, whenever a cabinet
;specific function is performed during gameplay,
;such as stalling the game to allow speech to continue
;or panning the sound effects for the ENV cab, and
;allowing a 2 player game in the UPR cab.
;the routine result is in Z flag, where Zero=False means that
;the game is an Upright. Here are some addresses
;that call the mode checking routine
;List of calls to Mode Jumper routine to HACK
;From Address Function Hack To
02EE End of Player game check other Upright
04F4 Display Start Options Upright
05CF Start 1 or 2 player on press Upright
;Since most functions need to be told that the game is ENV, I
;will change the mode checking rouine to always report ENV.
;Then I can specifically change the routines that conversely
;need to think the mode is upright.
;ADD ENVIROMENTAL 2 PLAYER START FEATURE !!!!!!!!!!!
;since the ENV cab will have no 2 player start button, I
;will hack in a way to start 2 player games. Just hold down
;the aiming knob while pressing 1P start to begin a 2 player
;game. Of course 1P and 2P start still work as before.
;Pertinant Game Functions
;Address Function
0x5c8 Get start press 1 or 2 player
0x5d7 Start 1 player game
0x5eb Start 2 player game
;choosing 1 or 2 players
;UNMODIFIED CODE SNIPPET
05C8: DB 00 in a,($00) ;read port
05CA: 2F cpl
05CB: E6 0C and $0C ;was either 1 or 2p start pressed?
05CD: 47 ld b,a ;make backup of pressed key in 'b'
05CE: C8 ret z ;leave if none pressed
05CF: E7 rst $20 ;check for Enviromental cab
05D0: 28 05 jr z,$05D7 ;if environmental, start 1 player
05D2: 78 ld a,b ;restore port reading to 'a'
05D3: E6 08 and $08 ;is it start 2?
05D5: 20 14 jr nz,$05EB ;if so start 2 player game
... ;otherwise, 1 player game, here
;NEW CODE SNIPPET
05C8: DB 00 in a,($00) ;read port
05CA: CB 5F bit 3,a ;was 2 Player Pressed?
05CC: 28 1D jr z,$05F9 ;if so, run 2 player game
05CE: CB 57 bit 2,a ;was 1 Player Pressed?
05D0: C0 ret nz ;leave if none pressed
05D1: DB 02 in a,($02) ;check for input on aim down
05D3: CB 67 bit 4,a ;was aim down held?
05D5: 28 14 jr z,$05F9 ;if so, run 2 player game
... ;otherwise, 1 player game, here
;Notice this also hacks out one of the mode jumper calls, so we don't have
;to hack that one otherwise
;COMPLETE LIST OF ROM CHANGES TO ADD ALL FUNCTIONALITY
;make jumper check routine always report ENV
;Address ROM:RELATIVE From To Checksum Change
*0x0023 loc-pg0.1c:0x0023 0xCB 0xE6 0x1B
*0x0024 loc-pg0.1c:0x0024 0x7F 0x00 0x81
;make 2 player routines think its always UPR
;Address ROM:RELATIVE From To Checksum Change
*0x02EF loc-pg0.1c:0x02EF 0xC8 0xC0 0xF8
*0x04F5 loc-pg0.1c:0x04F5 0x28 0x20 0xF8
;add hack to allow aim-down plus 1p to start a 2p game (see code snippets above)
;Address ROM:RELATIVE From To Checksum Change
*0x05CA loc-pg0.1c:0x05D8 0x2F 0xCB 0x9C
*0x05CB loc-pg0.1c:0x05D9 0xE6 0x5F 0x79
*0x05CC loc-pg0.1c:0x05DA 0x0C 0x28 0x1C
*0x05CD loc-pg0.1c:0x05DB 0x47 0x1D 0xD6
*0x05CE loc-pg0.1c:0x05DC 0xC8 0xCB 0x03
*0X05CF loc-pg0.1c:0x05DD 0xE7 0x57 0x70
*0x05D0 loc-pg0.1c:0x05DE 0x28 0xC0 0x98
*0x05D1 loc-pg0.1c:0x05DF 0x05 0xDB 0xD6
*0x05D2 loc-pg0.1c:0x05E0 0x78 0x02 0x8A
*0x05D3 loc-pg0.1c:0x05E1 0xE6 0xCB 0xE5
*0x05D4 loc-pg0.1c:0x05E2 0x08 0x67 0x5F
*0x05D5 loc-pg0.1c:0x05E3 0x20 0x28 0x08
----
Checksum Change Total: 0x4A
;Adjust a junk 0xff byte to cancel out the checksum change we have caused.
;Checksum Fix
;Address ROM:RELATIVE From To
*0x0005 loc-pg0.1c:0x0005 0xFF 0xB5 ;(0xFF-0x4A = 0xB5)
;MAKE ALL "*" CHANGES TO "loc-pg0.1c" ROM to apply patch.