serial.h

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    // of characters received after an xoff (as currently defined
    // by the IOCTL_SERIAL_XOFF_COUNTER ioctl) is sent.
    //
    PIRP CurrentXoffIrp;

    //
    // Holds the number of bytes remaining in the current write
    // irp.
    //
    // This location is only accessed while at interrupt level.
    //
    ULONG WriteLength;

    //
    // Holds a pointer to the current character to be sent in
    // the current write.
    //
    // This location is only accessed while at interrupt level.
    //
    PUCHAR WriteCurrentChar;

    //
    // This is a buffer for the read processing.
    //
    // The buffer works as a ring.  When the character is read from
    // the device it will be place at the end of the ring.
    //
    // Characters are only placed in this buffer at interrupt level
    // although character may be read at any level. The pointers
    // that manage this buffer may not be updated except at interrupt
    // level.
    //
    PUCHAR InterruptReadBuffer;

    //
    // This is a pointer to the first character of the buffer into
    // which the interrupt service routine is copying characters.
    //
    PUCHAR ReadBufferBase;

    //
    // This is a count of the number of characters in the interrupt
    // buffer.  This value is set and read at interrupt level.  Note
    // that this value is only *incremented* at interrupt level so
    // it is safe to read it at any level.  When characters are
    // copied out of the read buffer, this count is decremented by
    // a routine that synchronizes with the ISR.
    //
    ULONG CharsInInterruptBuffer;

    //
    // Points to the first available position for a newly received
    // character.  This variable is only accessed at interrupt level and
    // buffer initialization code.
    //
    PUCHAR CurrentCharSlot;

    //
    // This variable is used to contain the last available position
    // in the read buffer.  It is updated at open and at interrupt
    // level when switching between the users buffer and the interrupt
    // buffer.
    //
    PUCHAR LastCharSlot;

    //
    // This marks the first character that is available to satisfy
    // a read request.  Note that while this always points to valid
    // memory, it may not point to a character that can be sent to
    // the user.  This can occur when the buffer is empty.
    //
    PUCHAR FirstReadableChar;

    //
    // Pointer to the lock variable returned for this extension when
    // locking down the driver
    //
    PVOID LockPtr;


    //
    // This variable holds the size of whatever buffer we are currently
    // using.
    //
    ULONG BufferSize;

    //
    // This variable holds .8 of BufferSize. We don't want to recalculate
    // this real often - It's needed when so that an application can be
    // "notified" that the buffer is getting full.
    //
    ULONG BufferSizePt8;

    //
    // This value holds the number of characters desired for a
    // particular read.  It is initially set by read length in the
    // IRP.  It is decremented each time more characters are placed
    // into the "users" buffer buy the code that reads characters
    // out of the typeahead buffer into the users buffer.  If the
    // typeahead buffer is exhausted by the read, and the reads buffer
    // is given to the isr to fill, this value is becomes meaningless.
    //
    ULONG NumberNeededForRead;

    //
    // This mask will hold the bitmask sent down via the set mask
    // ioctl.  It is used by the interrupt service routine to determine
    // if the occurence of "events" (in the serial drivers understanding
    // of the concept of an event) should be noted.
    //
    ULONG IsrWaitMask;

    //
    // This mask will always be a subset of the IsrWaitMask.  While
    // at device level, if an event occurs that is "marked" as interesting
    // in the IsrWaitMask, the driver will turn on that bit in this
    // history mask.  The driver will then look to see if there is a
    // request waiting for an event to occur.  If there is one, it
    // will copy the value of the history mask into the wait irp, zero
    // the history mask, and complete the wait irp.  If there is no
    // waiting request, the driver will be satisfied with just recording
    // that the event occured.  If a wait request should be queued,
    // the driver will look to see if the history mask is non-zero.  If
    // it is non-zero, the driver will copy the history mask into the
    // irp, zero the history mask, and then complete the irp.
    //
    ULONG HistoryMask;

    //
    // This is a pointer to the where the history mask should be
    // placed when completing a wait.  It is only accessed at
    // device level.
    //
    // We have a pointer here to assist us to synchronize completing a wait.
    // If this is non-zero, then we have wait outstanding, and the isr still
    // knows about it.  We make this pointer null so that the isr won't
    // attempt to complete the wait.
    //
    // We still keep a pointer around to the wait irp, since the actual
    // pointer to the wait irp will be used for the "common" irp completion
    // path.
    //
    ULONG *IrpMaskLocation;

    //
    // This mask holds all of the reason that transmission
    // is not proceeding.  Normal transmission can not occur
    // if this is non-zero.
    //
    // This is only written from interrupt level.
    // This could be (but is not) read at any level.
    //
    ULONG TXHolding;

    //
    // This mask holds all of the reason that reception
    // is not proceeding.  Normal reception can not occur
    // if this is non-zero.
    //
    // This is only written from interrupt level.
    // This could be (but is not) read at any level.
    //
    ULONG RXHolding;

    //
    // This holds the reasons that the driver thinks it is in
    // an error state.
    //
    // This is only written from interrupt level.
    // This could be (but is not) read at any level.
    //
    ULONG ErrorWord;

    //
    // This keeps a total of the number of characters that
    // are in all of the "write" irps that the driver knows
    // about.  It is only accessed with the cancel spinlock
    // held.
    //
    ULONG TotalCharsQueued;

    //
    // This holds a count of the number of characters read
    // the last time the interval timer dpc fired.  It
    // is a long (rather than a ulong) since the other read
    // completion routines use negative values to indicate
    // to the interval timer that it should complete the read
    // if the interval timer DPC was lurking in some DPC queue when
    // some other way to complete occurs.
    //
    LONG CountOnLastRead;

    //
    // This is a count of the number of characters read by the
    // isr routine.  It is *ONLY* written at isr level.  We can
    // read it at dispatch level.
    //
    ULONG ReadByIsr;

    //
    // This holds the current baud rate for the device.
    //
    ULONG CurrentBaud;

    //
    // This is the number of characters read since the XoffCounter
    // was started.  This variable is only accessed at device level.
    // If it is greater than zero, it implies that there is an
    // XoffCounter ioctl in the queue.
    //
    LONG CountSinceXoff;

    //
    // This ulong is incremented each time something trys to start
    // the execution path that tries to lower the RTS line when
    // doing transmit toggling.  If it "bumps" into another path
    // (indicated by a false return value from queueing a dpc
    // and a TRUE return value tring to start a timer) it will
    // decrement the count.  These increments and decrements
    // are all done at device level.  Note that in the case
    // of a bump while trying to start the timer, we have to
    // go up to device level to do the decrement.
    //
    ULONG CountOfTryingToLowerRTS;

    //
    // This ULONG is used to keep track of the "named" (in ntddser.h)
    // baud rates that this particular device supports.
    //
    ULONG SupportedBauds;

    //
    // This value holds the span (in units of bytes) of the register
    // set controlling this port.  This is constant over the life
    // of the port.
    //
    ULONG SpanOfController;

    //
    // This value holds the span (in units of bytes) of the interrupt
    // status register associated with this port.  This is constant
    // over the life of the port.
    //
    ULONG SpanOfInterruptStatus;

    //
    // Hold the clock rate input to the serial part.
    //
    ULONG ClockRate;

    //
    // The number of characters to push out if a fifo is present.
    //
    ULONG TxFifoAmount;

    //
    // Set to indicate that it is ok to share interrupts within the device.
    //
    ULONG PermitShare;

    //
    // Holds the timeout controls for the device.  This value
    // is set by the Ioctl processing.
    //
    // It should only be accessed under protection of the control
    // lock since more than one request can be in the control dispatch
    // routine at one time.
    //
    SERIAL_TIMEOUTS Timeouts;

    //
    // This holds the various characters that are used
    // for replacement on errors and also for flow control.
    //
    // They are only set at interrupt level.
    //
    SERIAL_CHARS SpecialChars;

    //
    // This structure holds the handshake and control flow
    // settings for the serial driver.
    //
    // It is only set at interrupt level.  It can be
    // be read at any level with the control lock held.
    //
    SERIAL_HANDFLOW HandFlow;


    //
    // Holds performance statistics that applications can query.
    // Reset on each open.  Only set at device level.
    //
    SERIALPERF_STATS PerfStats;

    //
    // This holds what we beleive to be the current value of
    // the line control register.
    //
    // It should only be accessed under protection of the control
    // lock since more than one request can be in the control dispatch
    // routine at one time.
    //
    UCHAR LineControl;

    //
    // We keep track of whether the somebody has the device currently
    // opened with a simple boolean.  We need to know this so that
    // spurious interrupts from the device (especially during initialization)
    // will be ignored.  This value is only accessed in the ISR and
    // is only set via synchronization routines.  We may be able
    // to get rid of this boolean when the code is more fleshed out.
    //
    BOOLEAN DeviceIsOpened;

    //
    // Set at intialization to indicate that on the current
    // architecture we need to unmap the base register address
    // when we unload the driver.
    //
    BOOLEAN UnMapRegisters;

    //
    // Set at intialization to indicate that on the current
    // architecture we need to unmap the interrupt status address
    // when we unload the driver.
    //
    BOOLEAN UnMapStatus;

    //
    // This is only accessed at interrupt level.  It keeps track
    // of whether the holding register is empty.
    //
    BOOLEAN HoldingEmpty;

    //
    // This variable is only accessed at interrupt level.  It
    // indicates that we want to transmit a character immediately.
    // That is - in front of any characters that could be transmitting
    // from a normal write.
    //
    BOOLEAN TransmitImmediate;

    //
    // This variable is only accessed at interrupt level.  Whenever
    // a wait is initiated this variable is set to false.
    // Whenever any kind of character is written it is set to true.
    // Whenever the write queue is found to be empty the code that
    // is processing that completing irp will synchonize with the interrupt.
    // If this synchronization code finds that the variable is true and that
    // there is a wait on the transmit queue being empty then it is
    // certain that the queue was emptied and that it has happened since
    // the wait was initiated.
    //
    BOOLEAN EmptiedTransmit;

    //
    // This simply indicates that the port associated with this
    // extension is part of a multiport card.
    //
    BOOLEAN PortOnAMultiportCard;


    //
    // We keep the following values around so that we can connect
    // to the interrupt and report resources after the configuration
    // record is gone.
    //

    //
    // Translated vector
    //

    ULONG Vector;

    //
    // Translated Irql
    //

    KIRQL Irql;


    //
    // Untranslated vector
    //

    ULONG OriginalVector;


    //
    // Untranslated irql
    //

    ULONG OriginalIrql;


    //
    // Address space
    //

    ULONG AddressSpace;


    //
    // Bus number
    //

    ULONG BusNumber;


    //
    // Interface type
    //

    INTERFACE_TYPE InterfaceType;


    //
    // Port index no for multiport devices
    //

    ULONG PortIndex;


    //
    // Indexed flag for multiport devices
    //

    BOOLEAN Indexed;

    //
    // Mask inverted mask for multiport devices
    //

    ULONG MaskInverted;

    //
    // Needed to add new devices to multiport boards