Template for CRTC transition when entering a part in the CPC MegaDemo.

part_leave.asm

;;
; CRTC R7 transition sample to leave a part
; From R7=0 to standard R7=30
; Krusty/Benediction November 2013

    org &8000

    run $
leave_part_transition
    call secure_vsync 


    ; We want R7=30
    ld bc, &bc00 + 7
    out (c), c
    ld bc, &bd00 + 30
    out (c),c 

    ; So we need to have a small screen here
    ld bc, &bc00 + 4
    out (c), c
    ld bc, &bd00 + 8
    out (c), c

 
    halt  
    halt  
    halt  

    ld bc, &bd00 + 4
    out (c), c
    ld bc, &bd00 + 38
    out (c), c

    call secure_vsync
    ; 19968 nops between the 2 vsyncs
    call secure_vsync
    ; 19968 nops between the 2 vsyncs
    jp $


;;
; Wait the next new vsync
secure_vsync
    ld b, &f5
_vbl
    in a, (c)
    rra
    jr c, _vbl
vsync
    ld b, &f5
_novbl
    in a, (c)
    rra
    jr nc, _novbl
    ret