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        CPU     Z80UNDOC
        RELAXED ON

        include "ports.inc"

        org     0x4000

        di
        im      0
        
        ld      a,M_NOROM+C_24MHZ+M_EXPAG
        out     (GSCFG0),a

        
        
        ld      a,0xC3 ; JP
        ld      (0x28),a
        ld      (0x30),a
        
        ld      hl,MP3_INT
        ld      (0x29),hl
        ld      hl,SD_INT
        ld      (0x31),hl
        
        ld      a,0x7F
        out     (INTENA),a
        out     (INTREQ),a
        ld      a,0x86
        out     (INTENA),a
        
        
        xor     a
        ld      (fin),a
        ld      (fout),a

        ld      a,0x81
        ld      (flags),a
        
        call    check
        ei
        
hloop
        halt
        jp      hloop

        
SD_INT
        ld      hl,fin
        inc     (hl)

        ld      hl,flags
        call    check_sd
        bit     7,(hl)
        call    nz,check_mp3
        ei
        ret

        
MP3_INT
        ld      hl,fout
        inc     (hl)
        
        ld      hl,flags
        call    check_mp3
        bit     0,(hl)
        call    nz,check_sd
        ei
        ret
        
        
check   
        ld      hl,flags
        
        bit     0,(hl)
        call    nz,check_sd
        
        bit     7,(hl)
        call    nz,check_mp3
        ret

check_sd
        ld      a,(fout)
        ld      c,a
        ld      a,(fin)
        ld      b,a
        sub     c
        cp      128
        jr      c,sd_start
        
        set     0,(hl)
        ret
        
sd_start        
        ld      a,C_DMA_SD
        out     (DMA_MOD),a
        ld      a,1
        out     (DMA_HAD),a
        ld      a,b
        add     a,a
        out     (DMA_MAD),a
        xor     a
        out     (DMA_LAD),a
        ld      a,0x80
        out     (DMA_CST),a
        
        res     0,(hl)
        ret

        
        
check_mp3
        ld      a,(fout)
        ld      c,a
        ld      a,(fin)
        ld      b,a
        sub     c
        jr      nz,mp3_start
        
        set     7,(hl)
        ret
        
mp3_start       
        ld      a,C_DMA_MP3
        out     (DMA_MOD),a
        ld      a,1
        out     (DMA_HAD),a
        ld      a,c
        add     a,a
        out     (DMA_MAD),a
        xor     a
        out     (DMA_LAD),a
        ld      a,0x80
        out     (DMA_CST),a

        res     7,(hl)
        ret
        
        
        
        
        
        

llloop
        ld      a,C_DMA_SD
        out     (DMA_MOD),a

        ld      a,1
        out     (DMA_HAD),a
        xor     a
        out     (DMA_MAD),a
        out     (DMA_LAD),a

        ld      a,0x80
        out     (DMA_CST),a

        in      a,(DMA_CST)
        and     0x80
        jr      nz,$-4

        
        
        ld      a,C_DMA_MP3
        out     (DMA_MOD),a
        
        ld      a,1
        out     (DMA_HAD),a
        xor     a
        out     (DMA_MAD),a
        out     (DMA_LAD),a

        ld      a,0x80
        out     (DMA_CST),a
        
        in      a,(DMA_CST)
        and     0x80
        jr      nz,$-4
        
        
        
        jp      llloop

fin     db      0
fout    db      0
flags   db      0