INT 4B - Virtual DMA Specification - COPY OUT OF DMA BUFFER
        AX = 810Ah
        DX = 0000h
        ES:DI -> DMA descriptor structure (see AX=8102h) with buffer ID,
                region segment/offset, and region size fields set
        BX:CX = starting offset into DMA buffer
Return: CF clear if successful
        CF set on error
            AL = error code (see AX=8102h)