Re: Parallel Worlds buggy staircases

by **qwertymodo** Sat 21 May 2016 - 3:25

Ok, so here's a much cleaner and somewhat labeled disassembly of the relevant code path. Still digging through it, but if anybody else can help me make heads or tails of what it's trying to do (i.e. why it's trying to reset $212c to a hardcoded value), that would be quite helpful. If not, I'll keep plugging away at it. Basically, I need to figure out if there are any conditions where the sty $1C *should* get executed, so I can add in a conditional branch instead of just nop-ing it out entirely.

Code:: seek($248000) jsr check_module jsl $89B06E rtl seek($248008) check_module: lda $10 cmp #$07 beq ++ cmp #$09 beq check_submodule cmp #$0B beq check_submodule cmp #$0E beq + rts check_submodule: lda $11 cmp #$23 nop; nop; // bne #$00 cmp #$0D bmi ++ rts +; lda $11 cmp #$02 beq + rts +; nop jsr unk_sub_1 inc sta $7EE003 cmp #$03 beq + rts +; lda #$00 sta $7EE003 lda $7EE002 inc sta $7EE002 cmp #$3C bpl + rts +; lda #$00 sta $7EE002 increase_minutes: lda $7EE001 inc sta $7EE001 cmp #$3C bpl increase_hours rts increase_hours: lda #$00 sta $7EE001 lda $7EE000 inc sta $7EE000 cmp #$18 bpl reset_hours jsr sub_19 bcc + rts +; nop nop nop jsl $82FF70 lda $8C cmp #$9F beq + jsl $8BFE72 bra ++ +; jsl $8BFE72 +; rts reset_hours: lda #$00 sta $7EE000 lda $1B beq + rts +; jsl $82FF74 jsl $82FF70 lda $8C cmp #$9F beq + jsl $8BFE70 bra ++ +; jsl $8BFE72 +; rts seek($248310) unk_sub_1: jsr unk_sub_2 jsr lens_of_truth_on jsl $82FF8C sep #$30 rts seek($248320) unk_sub_2: lda $7EF273 inc sta $7EF273 cmp #$3C beq + rts +; lda #$00 sta $7EF273 lda $7EF272 inc sta $7EF272 cmp #$3C bpl + rts +; lda #$00 sta $7EF272 lda $7EF271 inc sta $7EF271 cmp #$3C bpl + rts +; lda #$00 sta $7EF271 lda $7EF270 inc sta $7EF270 cmp #$63 bpl + rts +; lda #$63 sta $7EF270 rts seek($248371) lens_of_truth_on: lda $1B bne + // Check if indoors rts // If outdoors, return +; lda $F2 // Check joypad 1 and #$70 // Mask XLR cmp #$50 // Check for X+R but not L bne + // If so, continue lda #$16 // #$16 = 0b00010110 sta $1C // BG1 off, BG2 on rts // Return +; cmp #$60 // If not pressing X+R beq + // Check for X+L but not R jsr lens_of_truth_off // Not pressing X+L, lens off rts // Return +; lda #$15 // #$15 = 0b00010101 sta $1C // BG1 on, BG2 off rts // Return seek($248390) lens_of_truth_off: ldy #$16 // BG1 off ldx $0414 // Check Layer 2 type lda $02894C,x // ?? bpl + // ?? ldy #$17 // BG1, BG2 on lda #$00 // Load #$00 +; cpx #$02 // Check Layer 2 type bne + // If "Dark Room", then lda #$03 // Load #$03 +; sty $1C // Set BG enable flags <==NOP this to fix stairs, but breaks LoT rts

by **qwertymodo** Sat 21 May 2016 - 3:46

Ok, so the bug was with the Lens of Truth code. Here's my initial attempt at a fix. One potential issue, the original code seemed to be returning a value in A, depending on the BG2 type (#$03 if "Dark Room", otherwise #$00), however, the only code that actually calls the subroutine immediately overwrites A without caring what's in it, so I'm going to go ahead and assume that code was vestigial, and in order to fit my fix into the same code space without having to relocate things, I'm not bothering to set A. I need to test more, but I've confirmed that the stairs are fixed, and the Lens of Truth functions normally.

Code:: // pw_lens_of_truth_fix.asm seek($248371) lda $1B bne + // Check if indoors rts // If outdoors, return +; lda $F2 // Check joypad 1 and #$70 // Mask XLR cmp #$50 // Check for X+R but not L bne + // If so, continue lda $1C // Load layer enable flags and #$FE // Disable BG1 sta $1C // Update layer enable flags rts // Return +; cmp #$60 // If not pressing X+R beq + // Check for X+L but not R jsr lens_of_truth_off // Not pressing X+L, lens off rts // Return +; lda $1C // Load layer enable flags and #$7D // Disable BG2 sta $1C // Update layer enable flags rts // Return lens_of_truth_off: lda $1C // Load layer enable flags ora #$02 // Enable BG2 tay ldx $0414 // Check Layer 2 type lda $02894C,x // ?? bpl + // ?? tya ora #$01 // Enable BG1 bra ++ +; tya +; sta $1C // Set BG enable flags rts // Return

by **Puzzledude** Sat 21 May 2016 - 7:03

Ok, so the bug was with the Lens of Truth code.

I was just thinking about this when you posted the MoN's disassembly, since the only additional code checking for BGs is the X+R trick to disable a layer to find Parallel-tower-keys.