; Simple working bootblock
    MACHINE 68000
    ORG 0

    dc.b    'D','O','S',0       ; DOS magic
    dc.l    0                   ; Checksum
    dc.l    880                 ; Rootblock

; Boot code - a1=IORequest, a6=ExecBase
boot_start:
    ; Save IORequest pointer (PC-relative)
    lea     SavedA1(pc),a0
    move.l  a1,(a0)

    ; Load game from disk
    move.w  #2,28(a1)           ; CMD_READ
    move.l  #$20000,40(a1)      ; io_Data
    move.l  #11776,36(a1)       ; io_Length (Exact game size)
    move.l  #1024,44(a1)        ; io_Offset
    
    jsr     -456(a6)            ; DoIO
    
    ; Check for Error
    tst.l   d0
    bne.s   .loadError

    ; Restore IORequest pointer
    lea     SavedA1(pc),a0
    move.l  (a0),a1
    
    ; Turn off motor
    move.w  #9,28(a1)           ; CMD_MOTOR
    move.l  #0,36(a1)
    jsr     -456(a6)            ; DoIO
    
    ; Jump to game
    jmp     $20000

.loadError:
    ; Error: Magenta Screen Loop
    move.w  #$F0F,$dff180
    bra.s   .loadError

SavedA1:
    dc.l    0

; Pad to 1024 bytes
    dcb.b   1024-(*-0),0