Difference between revisions of "Super Mario Bros. 3:Notes"

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Back to [[Super Mario Bros. 3|Super Mario Bros. 3]] page.
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{{notes|game=Super Mario Bros. 3}}
 
=Disassembly/reverse engineering notes=
 
=Disassembly/reverse engineering notes=
All values given are hexadecimal unless noted otherwise.
 
Various important bits of code follow below. Unless marked as "subroutine" you can NOT jump directly to these addresses, and even then there might be side effects.
 
  
Wording on countdown timers: "cycles from xx" means the timer is repeatedly set to xx, allowed to reach 0, gets set to xx again etc.
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* NN: all values are hexadecimal and at least two digits (e.g. 0F, not F) unless noted otherwise.
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* $NN or $NNNN: a memory address.
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* Countdown timer: a byte in memory set to some value, decremented every frame and when it reaches 0 something is usually set up to happen. Many timers are cyclic, meaning that they are being re-set and reused immediately after reaching 0.
  
 
==Player physics/movement==
 
==Player physics/movement==
  
 
===Horizontal movement===
 
===Horizontal movement===
* If the player holds L/R the horizontal velocity $BD will start to increase (todo: what's the exact increment?) at around 1 per frame. The same acceleration is always used when walking/running/dashing.
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* If the player holds L/R the horizontal velocity $BD will start to increase (to-do: what's the exact increment?) at around 1 per frame. The same acceleration is always used when walking/running/dashing.
 
* abs($BD) can at most reach a limit that varies depending on things below.
 
* abs($BD) can at most reach a limit that varies depending on things below.
* If walking, the limit is 18 (24 dec).
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* If WALKING, the limit is 18.
 
* If player holds B,  
 
* If player holds B,  
** The limit is raised to 28 (40 dec) and velocity is allowed to increase again.
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** The limit is raised to 28 and $BD is allowed to increase again. This is RUNNING.
** As long as abs($BD) stays >= 28, the P-timer $515 cycles from 7, and every time it elapses an arrow is added to the P-meter.
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** When abs($BD) is >= 28, you are DASHING and the P-timer $515 cycles from 7. Every time it elapses an arrow is added to the P-meter.
 
** When the P starts blinking, the player is in "flight mode":
 
** When the P starts blinking, the player is in "flight mode":
*** 1) The limit is raised to 38 (56 dec) and $BD is allowed to increase again.
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*** 1) The limit is raised to 38 and $BD is allowed to increase again.
*** 2) The P-timer is LOCKED to the value 15 (why that value? could be anything but 0).
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*** 2) The P-timer is LOCKED to the value 0F (don't know if the exact value has significance).
*** 3) Jumping now launches into flight, (if player has a suitable powerup, otherwise just jumping high).
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*** 3) Pressing A at this point launches the player into flight/super-jump, indicated by $57B being set to 1.
*** 4) The flight-limit countdown timer $056E is set to XX (todo: fix value).
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*** 4) The flight duration timer $56E is set to XX (to-do: look up the value).
** Player exits "flight-mode" when one of the following happens: (NOT COMPLETE)
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** Player exits "flight-mode" ($57B = 0) when one of the following happens: (to-do: incomplete)
*** Touches ground.
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*** 1) Player touches ground.
*** Flight-limit timer $056E elapses.
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*** 2) Flight-limit timer $56E elapses.
** Once no longer in "flight-mode", the P-meter timer cycles from 23. Every time it elapses an arrow is removed from the P-meter.
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*** 3) Player lets go of the A button.
** You only begin to fill up the P-meter again if you accelerate to abs($BD) >= 28.
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** Once no longer in "flight-mode", the P-timer $515 cycles from 23. Every time it elapses an arrow is removed from the P-meter.
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** You can only refill the P-meter again by accelerating to abs($BD) >= 28 as above. (If $515 hasn't had time to elapse, i.e. the P-meter hasn't decreased, you can stay "eligible" for $57B flight-mode by doing short hops of flight and staying at >= 28.)
  
 
===$AC5A Jump power===
 
===$AC5A Jump power===
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  $BFDA:20 93 BF  JSR $BF93 ; UNKNOWN
 
  $BFDA:20 93 BF  JSR $BF93 ; UNKNOWN
 
  $BFDD:60        RTS
 
  $BFDD:60        RTS
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{{Internal Data|game=Super Mario Bros. 3}}

Latest revision as of 08:24, 12 December 2018

Disassembly/reverse engineering notes

  • NN: all values are hexadecimal and at least two digits (e.g. 0F, not F) unless noted otherwise.
  • $NN or $NNNN: a memory address.
  • Countdown timer: a byte in memory set to some value, decremented every frame and when it reaches 0 something is usually set up to happen. Many timers are cyclic, meaning that they are being re-set and reused immediately after reaching 0.

Player physics/movement

Horizontal movement

  • If the player holds L/R the horizontal velocity $BD will start to increase (to-do: what's the exact increment?) at around 1 per frame. The same acceleration is always used when walking/running/dashing.
  • abs($BD) can at most reach a limit that varies depending on things below.
  • If WALKING, the limit is 18.
  • If player holds B,
    • The limit is raised to 28 and $BD is allowed to increase again. This is RUNNING.
    • When abs($BD) is >= 28, you are DASHING and the P-timer $515 cycles from 7. Every time it elapses an arrow is added to the P-meter.
    • When the P starts blinking, the player is in "flight mode":
      • 1) The limit is raised to 38 and $BD is allowed to increase again.
      • 2) The P-timer is LOCKED to the value 0F (don't know if the exact value has significance).
      • 3) Pressing A at this point launches the player into flight/super-jump, indicated by $57B being set to 1.
      • 4) The flight duration timer $56E is set to XX (to-do: look up the value).
    • Player exits "flight-mode" ($57B = 0) when one of the following happens: (to-do: incomplete)
      • 1) Player touches ground.
      • 2) Flight-limit timer $56E elapses.
      • 3) Player lets go of the A button.
    • Once no longer in "flight-mode", the P-timer $515 cycles from 23. Every time it elapses an arrow is removed from the P-meter.
    • You can only refill the P-meter again by accelerating to abs($BD) >= 28 as above. (If $515 hasn't had time to elapse, i.e. the P-meter hasn't decreased, you can stay "eligible" for $57B flight-mode by doing short hops of flight and staying at >= 28.)

$AC5A Jump power

$AC5A:A5 BD     LDA $00BD			; Load player horz velocity
$AC5C:10 03     BPL $AC61			; If negative,
$AC5E:20 0F DD  JSR $DD0F			; 	take absolute value
$AC61:4A        LSR				; Divide by 16
$AC62:4A        LSR
$AC63:4A        LSR
$AC64:4A        LSR
$AC65:AA        TAX				; X = A, going to use it as an index
$AC66:AD 47 A6  LDA $A647			; Load default jump velocity
$AC69:38        SEC				
$AC6A:FD 48 A6  SBC $A648,X			; Subtract from the jump velocity (remember lower means more power) using the table 00,02,04,08.
						; Thus a higher horizontal speed means a more powerful jump.
$AC6D:85 CF     STA $00CF			; Store as new vertical velocity.

$ACA1 Application of gravity

$ACA1:A0 05     LDY #$05		; Y = default falling gravity
$ACA3:A5 CF     LDA $00CF		; Load current vertical velocity
$ACA5:C9 E0     CMP #$E0		; 
$ACA7:10 0D     BPL $ACB6		; If currently rising and v vel is still faster than E0,
$ACA9:AD 79 05  LDA $0579		; 	Don't know what 0579 is... unused? Debugger never sees a nonzero value.
$ACAC:D0 0D     BNE $ACBB
$ACAE:A5 17     LDA $0017		; 	Read gamepad. 80 is jump key, so value will appear negative!
$ACB0:10 04     BPL $ACB6		; 	If jump pressed,
$ACB2:A0 01     LDY #$01		; 		Y = jump gravity (lower than normal)
$ACB4:D0 05     BNE $ACBB		; 
$ACB6:A9 00     LDA #$00		; This is run if jump key is NOT pressed
$ACB8:8D 79 05  STA $0579		; 	So what does it do? 
$ACBB:98        TYA			; A=Y
$ACBC:18        CLC			;
$ACBD:65 CF     ADC $00CF		; Add gravity to current vertical velocity
$ACBF:85 CF     STA $00CF		; And store back

So, jumps are aborted either by the user releasing the button (bit 7 in 0017 is zero) or the 00CF is more positive than E0. Since SOME gravity is always applied, this ensures jumps are aborted.


$BFCC (Subroutine) Clamp Y velocity to the maximum

$BFCC:A5 CF     LDA $00CF			; Load current vertical velocity
$BFCE:30 08     BMI $BFD8			; Negative? Then skip clamping.
$BFD0:C9 40     CMP #$40			; #$40 is the maximum fall vel (note: gravity is added afterwards so the effective value is 45) 
$BFD2:30 04     BMI $BFD8			; Less than this? Then skip clamping.
$BFD4:A9 40     LDA #$40			; Replace $00CF with the maximum fall vel.
$BFD6:85 CF     STA $00CF
$BFD8:A2 12     LDX #$12			; UNKNOWN
$BFDA:20 93 BF  JSR $BF93			; UNKNOWN	
$BFDD:60        RTS


Internal Data for Super Mario Bros. 3

ROM MapRAM MapText TableNotesTutorials