palace_continue

Continue from any palace

This routine was copied and optimized from Digshake's randomizer.

The basic idea is to save the room code for the start of a palace when you enter a palace area. You can then reuse the room code to continue at the beginning of that palace.

Digshake was using $fb0/$fb1 to store these values, but I think this memory may have some other use -- at least it isn't initialized to zeros.

Instead, I'm storing the room code at $6fe/$6ff, which is the end/ unused area of the item availability bitmap. This area is zeroed out upon each new game. Depending on having zeroed memory allowed me to optimize the routine a bit and squeeze it into a smaller amount of the precious bank7 free space.

asm b=7 0xd39a
    sta $0707           ; World number is in A register, store it
    cmp #$03            ; World less than 3
    bmi $0e             ; yes, branch to end
    lda $06fe           ; Has the room code already been stored
    bne $09             ; yes, branch to end
    lda $0561           ; get the current room code
    sta $06ff           ; store it in $6ff
    inc $06fe           ; mark it as stored in $6fe
    lda $0707           ; End: reload the world number
    rts                 ; Return

    lda $06ff           ; Load the room code
    sta $0561           ; Store it in the room code location
    jsr $a057           ; something to do with levels and XP?
    lda $0707           ; Load the world number
    rts                 ; return

    sty $0707           ; Zero out the world number (return to overworld)
    sty $06fe           ; Zero out the room-code-stored marker
    rts                 
.org $cbaa
    jsr $d39a           ; Entering a new area, maybe store room number
.org $cf92
    jsr $d3c0           ; Leaving an area, clear the room-code-stored-marker
.org $cad0
    jsr $d3b3           ; Refresh the room marker and load the world number
    cmp #$03            ; World 3 or greater (palaces)
    bcs $07             ; jump to restore/continue routine
.org $cae3
    nop                 ; zap out the code which clears the room number
    nop
    nop
.end