Club Amiga de Montreal - CAM/CAM_CD_1.iso/files/171.lha/SupLib/qint.doc

Text File | 1988-04-28 | 5KB | 133 lines

               QINT DOCUMENTATION

        Matthew Dillon

        [e-mail]    ARPA
        ...!ihnp4!ucbvax!dillon    USENET

NOTE!!!!!   Lattice Users must replace the 'jsr _geta4' call with the
        appropriate call to retrieve the address register for the
        small data model before compiling!    You might have to make
        other modifications as well (I don't know since I don't
        have Lattice).


The Calls:
    char oldpri;        range -128 to 127
    char newpri;
    char pri;
    long signum;        0 .. 31

    void (*vector)();   function vector returning nothing
    void (*oldvec)();


    While active Q interrupt vectors exist, the tc_ExceptCode in the
    task structure will be modified.  The old tc_ExceptCode is used if
    an unknown exception occurs (one that is not a Q interrupt).

    oldpri = SetQPri(newpri)

    Set the task's current Q priority.  Any Q interrupts of lower or
    equal priority that occur will be queued until the priority is
    dropped sufficiently.

    The initial task priority is -128 (essentially allowing all Q
    interrupts -127 to 127 to occur).

    oldvec = SetQVector(signum, vector, arg, pri)

    If vector is non-null, enables the exception at the specified
    priority (-127 to 127).  specified vector is called in a C
    compatible way with one user argument (arg).  Specifying a
    priority of -128 does not make sense because this is the lowest
    allowed priority and the Q interrupt will thus never occur.

    If vector is null, the exception and Q interrupt is disabled.
    After the last Q interrupt is removed, tc_ExceptCode is restored
    to its original value.


BUGS:
    The only bug that I know of is a problem with EXEC.

    What is Good:    An exception will not occur while one is Forbid()n
    What is Bad:    If an exception comes in while Forbid()n, it will
            NOT be immediately entered when you Permit().

    Whoops.  The exception *will* occur when EXEC next checks its
    signals and exceptions, which occurs on the obvious EXEC library
    calls (SetExcept(), SetSignal(), etc...)  and perhaps Wait().

    In most cases you can ignore the problem.


GENERAL WORKINGS OF Q INTERRUPTS:

    If you know how EXEC signals and the 68000 interrupt structure
    works, then you know how Q interrupts work.  Simply replace
    "processor" with "task" and "0-7" with "-128 to 127" for task
    Q interrupt priorities (this is different from the Task's
    scheduler priority).

    Q interrupts work just like 68000 interrupts.  If the task is
    currently running at a Q interrupt priority N, only Q interrupts
    of HIGHER priority can occur.  Q interrupts of LOWER OR EQUAL
    priority are queued and will occur as soon as the priority is
    lowered.  Everything occurs in priority order, the highest priority
    pending interrupt is always the one running (or the task's main
    routine if it has the highest priority).

    Thus, while a Q interrupt handler is running at some specific
    priority, other Q interrupts at the same priority will wait
    until the first one finishes and then execute in a FIFO fashion.

THE INTERRUPT VECTOR ROUTINE:

    A specific Q interrupt vector is a C subroutine called with one
    longword argument (that specified when you SetQVector()'d it).
    This works fine with the small model.

    The handler runs with all normal EXEC processing enabled, and in
    the context of its task.  It can be viewed almost as a subroutine
    call from the task.  However, you must be careful about the
    reentrancy of certain functions.  STDIO, DOS, and many other
    library calls are not reentrant, and you must use SetQPri() to
    ensure such calls are not interrupted.    NOTE that you CAN mix
    certain calls.    I don't have much info on what combinations work,
    but certainly most library calls that do not depend on being
    called singularly from tasks will work (for example, GetMsg()).
    And, of course, if all your handler does is make some small
    calculations this can interrupt anything.

    If you cause an exception (the same exception) from within the
    handler, it will be remembered.  (That is, the signal is cleared
    before the handler is called), and occur after your handler
    returns.

USES FOR Q INTERRUPTS:

    Use #1:     To be able to execute menu options which do not effect
            the 'current' operation.  E.G. if you are doing a
            ray tracing you could make the intuition window's
            signal bit a Q interrupt and handle Intuition messages
            that way....   The main loop generating the ray
            tracing would not have to continuously check for
            Intuition messages.

    Use #2:     Lets say you are writing a terminal program and want
            to display data comming in smoothly while sending a
            file.  While this can be done easily with the
            asynchronous ability of IO devices, it would be even
            easier if you handled the receive with a Q interrupt...
            that way, you could display received data (SendIO to
            the console device) even if the file sender is in
            the middle of a DOS call to read the next file block.

    Many more uses (I hope!).

                -Matt