initstabilise   lda $d012
                ldx #10          ; 2
-               dex              ;   (10 * 5) + 4
                bpl -            ; 54
                nop              ; 2
                eor $d012 - $ff,x; 5 = 63
                bne initstabilise; 7 = 70

                [...]; timer setup

start:  ldx $d011
        bpl start:
loop:   pha
        cpx $d012
        pla
        inc safe_mem,x
        bcs loop:

sync:
    lda $d012   ; will be zero on cycles 0,1,2,3,4,5 or 6
    bne sync

    .res 25,$ea ; replace this with 50 cycles of init code

    lsr $d012   ; if it's zero, either we're too early on line 0, or we're on line 256..  
    bcc sync    ; fall through if we read on cycle 62, 56 after cycle 6

sync:
    ldy #val
    lax $d012
    bne sync
    // here we are at cycle 3..9 of rasterline $00 (or 2..8 of rasterline $100)
    /*
    // 50 cycles of init code go here
    */
    // after that init code block we are @cycle 53..59 of rasterline $00(52..58 of line $100)
    lda $d012   // the R-cycle occurs @cycle 57..63 -> 63 = cycle 0 of line 1
                // in rasterline $100 this will end up @cycle 56..62, thus always without reaching the next line 
    beq sync    // branch not taken only when line 1 is reached

sync:
    lax $d012
    bne sync
    /*
    // 50 cycles of init code go here
    */
    lda $d012
    //-p-a-g-e-b-r-e-a-k-
    beq sync

sync:
    inc $d012   ; result will be zero on cycles 0-7 or 8 of raster line $ff
    bne sync    ; (or very rarely, cycle 9..62)

    .res 27,$ea ; wait 62-8=54 cycles. Replace with 54 cycles of init code

    inc $d012   ; if result is nonzero then we are too late.
    bne sync    ; carry on if we read on cycle 62, 62 cycles after cycle 0