( Save ACIA conf )
ACIA_CTL
: ACIA_CTL [ LITN ] ;
ACIA_IO
: ACIA_IO [ LITN ] ;
ACIA_MEM
: ACIA_MEM [ LITN ] ;
( Memory layout
  +0 ACIAR>
  +2 ACIAW>
  +4 ACIA(
  +6 ACIA)
)

(xentry) ~ACIA
    AF PUSHqq,
    HL PUSHqq,
    DE PUSHqq,

	( Read our character from ACIA into our BUFIDX )
    ACIA_CTL INAn,
    0x01 ANDn,   ( is ACIA rcv buf full? )
    IFNZ,
        ( correct interrupt cause )
        ( +2 == ACIAW> )
        ACIA_MEM 2+ LDHL(nn),
        ( is it == to ACIAR>? )
        ( +0 == ACIAR> )
        DE ACIA_MEM LDdd(nn),
        ( carry cleared from ANDn above )
        DE SBCHLss,
        IFNZ, ( buffer full? )
            ( no, continue )
            DE ADDHLss, ( restore ACIAW> )
            ( buffer not full, let's write )
            ACIA_IO INAn,
            (HL) A LDrr,

            ( advance W> )
            HL INCss,
            ( +2 == ACIAW> )
            ACIA_MEM 2+ LD(nn)HL,
            ( +6 == ACIA) )
            DE ACIA_MEM 6 + LDdd(nn),
            DE SUBHLss,
            IFZ, ( end of buffer reached? )
                ( yes )
                ( +4 == ACIA( )
                ACIA_MEM 4 + LDHL(nn),
                ( +2 == ACIAW> )
                ACIA_MEM 2+ LD(nn)HL,
            THEN,
        THEN,
    THEN,

    DE POPqq,
    HL POPqq,
    AF POPqq,
    EI,
    RETI,