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These functions provide the capability to invoke Intel 80x86
processor-related functions directly from a program.  Functions that apply
to the Intel 8086 CPU apply to that family including the 80286, 80386 and
80486 processors.  The following functions are defined:

_chain_intr
    chain to the previous interrupt handler

_disable
    disable interrupts

_enable
    enable interrupts

FP_OFF
    get offset part of far pointer

FP_SEG
    get segment part of far pointer

inp
    get one byte from hardware port

inpw
    get two bytes (one word) from hardware port

int386
    cause 386/486 CPU interrupt

int386x
    cause 386/486 CPU interrupt, with segment registers

int86
    cause 8086 CPU interrupt

int86x
    cause 8086 CPU interrupt, with segment registers

intr
    cause 8086 CPU interrupt, with segment registers

MK_FP
    make a far pointer from the segment and offset values

nosound
    turn off the speaker

outp
    write one byte to hardware port

outpw
    write two bytes (one word) to hardware port

segread
    read segment registers

sound
    turn on the speaker at specified frequency