Donkey Kong (NES) Level 133 Fix?

[ColecoFan1981]

Having gotten myself acquainted with the logic for what triggers the "kill screen" on both the arcade and NES versions of Donkey Kong, may I ask you how you guys have managed to come up with a fix for Level 133 on the latter version?

 

For your information, these are the links I visited to get this info:

http://www.donhodges.com/how_high_can_you_get.htm

(arcade version)

 

http://metopal.com/2012/03/24/porting-the-kill-screen/

(NES version)

 

What I wish to do to correct the kill screen for the NES DK is to make a similar fix as to what Don Hodges did for the arcade version.

 

Here's the original NES version code for the kill screen:
 

CB7E  A4 54     LDY $54      ; loads current level number into Y

CB80  C8        INY          ; increment level number by 1

CB81  20 D1 F4  JSR $F4D1    ; jump to subroutine to calculate level number tile

CB84  A9 00     LDA #$00     ; set sign of bonus number as positive

CB86  85 2C     STA $2C      ; store this number in variable

CB88  A9 80     LDA #$80     ; load A with max bonus timer value (8000 bonus points)

CB8A  88        DEY          ; decrement variable in Y by 1

CB8B  C0 04     CPY #$04     ; check if level number < 5

CB8D  10 03     BPL $CB92    ; check for negative flag
                                                        
CB8F  B9 07 C2  LDA $C207,Y  ; load bonus timer value from memory                                                        

CB92  85 2E     STA $2E      ; store in bonus timer value queue

 

My proposed fix for this, based on Hodges' fix for the arcade version:
 

CB7E  A4 54     LDY $54      ; loads current level number into Y

CB80  C0 03     CPY #$03     ; check if level number >= 4

CB82  90 02     BCC $CB86    ; if level 1, 2 or 3 (variables $00 thru $02), continue with code normally

CB84  A0 03     LDY #$03     ; otherwise, load Y with #$03 (level 4)

CB86  C8        INY          ; increment level number by 1 (only if for level variables $00 thru $02)

CB87  20 D1 F4  JSR $F4D1    ; jump to subroutine to calculate level number tile

CB8A  A9 00     LDA #$00     ; set sign of bonus number as positive

CB8C  85 2C     STA $2C      ; store this number in variable

CB8E  B9 07 C2  LDA $C207,Y  ; load bonus timer value from memory

CB91  85 2E     STA $2E      ; store in bonus timer value queue

What I want to do is make it check the level number right after it's loaded into the variable that is stored at $0054 in the game's RAM. We want to compute the bonus timer based on the level number, so that level 4 and up will always start with 8000 points on the bonus timer. If the level number is 4 or higher, then we set a carry flag for, and this means we also only want it to increment the level number if we're on levels 1, 2 or 3 (variables $00 thru $02). The subroutine jump to $F4D1, which follows the INY, must also be modified for a check to see if the level number is 9 or higher, and if we're at level 9, to keep it there via a similar carry flag.

 

~Ben

Edited October 17, 2022 by ColecoFan1981