SDCC/ASM. Play BASIC PLAY sentence from MSX-DOS

// by NataliaPC (@ishwin74)
void basic_play(void *params) __naked __sdcccall(1)
{
    params;
    __asm
        push hl                                     ; Store the Param 'params'

        ld   hl, #.play_call                        ; Copy routine to _heap_top
        ld   de, (_heap_top)                        ; _heap_top must be >= 0x8000
        ld   bc, #.play_call_end - .play_call
        ldir

        pop  hl                                     ; Copy the PLAY sentence from 'params'
        push de                                     ; Store the start of PLAY sentence
        ld   bc, #80                                ; Max length of PLAY sentence
        ldir

        ld   ix, (_heap_top)
        jp   (ix)

    .play_call:
        pop  hl                                     ; Recover the start of PLAY sentence

        di                                          ; Store current slot configuration
        in   a,(0xa8)
        push af
        and  #0b11110000                            ; Set ROMs pagination
        ei
        out  (0xa8),a       // TODO: take care of subslots

                            // TODO: hardcoded. Read (0x39AE) to get the PLAY address
        call 0x73e5                                 ; HL = parameters for PLAY as Asciiz

    .wait_loop:
        ld   hl, #VCBA
        ld   a, (hl)
        inc  hl
        or (hl)
        ld   hl, #VCBB
        or (hl)
        inc  hl
        or (hl)
        ld   hl, #VCBC
        or (hl)
        inc  hl
        or (hl)
        jr   nz, .wait_loop

        pop  af
        di
        ei
        out  (0xa8),a       // TODO: take care of subslots
        ret

    .play_call_end:
    .play_sentence:
    __endasm;
}