NAME
        CardInterface -- Determine the type of card interface.

   SYNOPSIS
        return = CardInterface()
        d0

        ULONG CardInterface( void );

   FUNCTION
        This function is used to determine the type of credit-card
        (hardware) interface available.  For the most part the
        card.resource hides the hardware details from devices within its
        function calls.  However should we need to provide a work-around
        because of differences, or limitations imposed by future interface
        hardware, this function must be used to identify which interface
        is available.

   RETURN
        A ULONG value as defined in card.h/i.

   NOTES
        In general only I/O devices (e.g., a device which interfaces
        with a modem card) would need to provide work-arounds,
        or alternative code.  An example would be a change in the way
        interrupt requests from the card are handled.  Specific details
        will be provided as need in the future.  I/O devices) should abort
        properly if this function returns a value which is unknown.

        Current implementations (see card.h/i) -

        CARD_INTERFACE_AMIGA_0
        -------------------------------------------------------------

        The card slot can be configured for use as an I/O interface
        by using the cardmisccontrol() function.

        The card slot inhibits writes to cards which do not negate
        the WP status bit.  This can be overridden by using the
        cardmisccontrol() function.

        Changes in the interrupt request line are latched by a gate-array,
        and have to be obtained via the status change mechanism provided
        when you call the owncard() function.  the interrupt is cleared
        when you return from the status change interrupt.  A level 2
        interrupt is generated.  Usually you will want to clear the
        interrupt on the card at this time, and signal() a task.  the irq
        line is the same as the RDY/BSY line.

        Changes in BVD1, WP, and RDY/BSY are also latched by the gate-array,
        and are obtainable via the status change mechanism provided by
        the owncard() function.  a level 2 interrupt is generated.

        Changes in BVD2 (also used for digital audio) have to be
        monitored via polling.  Generally this will cause no problem.
        Monitoring changes in BVD1 & BVD2 to monitor for low battery
        condition can be handled by a low priority tool which periodically
        checks the condition of both lines using the readcardstatus()
        function.

        As of card.resource V39 (check VERSION in resource base), the
        cardmisccontrol() function can be used to enable/disable
        status change interrupts for changes in BVD1, BVD2, and the
        RDY/BSY status line.  Status change interrupts for WR
        (Write-protect enable/disable) are always enabled.  The default
        state of enabled/disabled status change interrupts noted above
        are unchanged, and automatically reset to the defaults when
        a card is removed, or when even a task releases ownership
        of the card.

        Some PC oriented eight (8) bit cards may require you read
        odd-byte I/O address registers at the corresponding even-byte
        address plus 64K.  There is sufficient I/O address space
        provided that exceeding I/O address space should not be a problem.

        Your code should wait at least 1 millisecond for Vpp to stabilize
        after voltage change (see cardprogramvoltage()).

    SEE ALSO
        cardmisccontrol(), resources/card.i, resources/card.h