update.doc

用C++写的RS232串口异步通讯功能模块

                             MCOMM 5.40 UPDATE NOTES

         The 5.40 version of MCOMM corrects two problems:

         1) Some UARTs miss transmit interrupts when they are ran in
            full duplex mode.  Code was added to detect missed
            interrupts and correct the situation.  This condition would
            cause previous versions of MCOMM to quit transmitting until
            the transmit buffer was flushed or the port closed and
            reopened.  This bug only showed up when operating in full
            duplex mode and only with some UARTs.  Version 5.40 has been
            tested by running several megabytes of data through 8250,
            16450, and 16550 UARTs in full duplex mode and never fails
            to detect a missed interrupt and correct for it.

         2) The loop that loads bytes into the transmit FIFOs (or the
            transmit hold register if the UART isn't a 16550) updates
            the transmit buffer output pointer in a register.  The loop
            is in the transmit interrupt handler and in previous
            versions of MCOMM5 the transmit interrupt handler code was
            called by the routine that started up the transmitter.  If a
            transmit interrupt occurred while the transmit start up code
            was within this loop, the buffer output pointer could be
            corrupted.  The result was scrambled output.  This only
            happened if the transmitter was sent a character, allowed to
            empty, and then immediately sent another character.  If only
            one character was sent at a time slowly, as in typing, or if
            the buffer was loaded up rapidly as in a program loop,
            everything was OK.  If characters were sent in a program loop
            that put a "small" delay between characters (character
            pacing), it often failed.  This was corrected by changing
            the transmit initiate routine so that it toggles the
            transmit interrupt enable bit in the UART's interrupt enable
            register to initiate transmit interrupts rather than calling
            the interrupt handler directly.


         ADDITIONS:

         An option was added to the async_open function to force FIFO
         mode off.  Previously you could OR the ComBase parameter with
         0x8000 and the code skipped over the check for a 16550 UART.
         If it was there and on, it stayed on.  If it was there and off,
         it stayed off.  You can now OR the ComBase parameter with
         0x4000 to force the FIFOs to be off.  If you don't OR anything
         with the ComBase parameter the FIFOs will be enabled if a 16550
         is present.

         To deal with problems with the Western Digital 16550, the ASYNC
         port structure is now one element longer.  The new element is
         called 'IERVal'.  Also options were added to allow you to open
         a port without enabling MSR interrupts, LSR interrupts, or
         both.  See the notes on the WD16550 in ASYNC.DOC for more
         information.




         Conversion LIBs and a batch file were added to support Zortech
         C / C++.  C++ header files and a C++ demo program for either
         Turbo C++ or Zortech C++ were added.

         Two new macros are now defined in COMM.H.  They are:

         async_txcnt(ASYNC *port) -- returns number of bytes left
                                     in the transmit buffer still to
                                     be transmitted.  Use async_txempty
                                     if you are waiting for 0 byte
                                     condition -- it's more efficient.

         async_rxfree(ASYNC *port) - returns bytes of free space left
                                     in the receive buffer.


         VIDEO FUNCTIONS:

         One minor bug was fixed.  The rd_scrnd function returned an
         incorrect pointer if the function was called with a request to
         read 0 bytes.  The result string was correct but the return
         value was wrong.  It now returns the correct pointer.

         A new global variable was added to control whether a displayed
         backspace character was destructive or non-destructive.
         Previously it was always destructive and that still is the
         default.  The variable is v_bksp.  Setting v_bksp to 0 will
         cause the backspace character to be non-destructive.




                            MCOMM 5.20 UPGRADE NOTES

            Major changes in this version of MCOMM are support for the
         16550 UART's FIFO mode of operation, changes in the header
         files, new time-out functions, and updated documentation.


         16550 UART SUPPORT:

            The async code now supports the 16550 UART's FIFO mode of
            operation.  Key features are:

            1) The async_open function automatically detects a 16550 and
               enables its FIFOs (can be optionally defeated).

            2) Functions are provided to set the receiver FIFO trigger
               level and to control the maximum number of bytes to load
               into the transmit FIFO at one time.

            3) The interrupt handler has been re-written to make most
               efficient use of the FIFO registers (they process
               multiple bytes per interrupt).

            ASYNC.DOC contains full descriptions of the new functions
            and changes made to the old functions.  It also has some
            information on how to set the receiver FIFO trigger level
            and the 'maximum number of bytes to transmit to the FIFOs at
            one time' level to achieve the best results.


         HEADER FILE CHANGES:

            Due to stricter type checking of newer compilers, several
            functions that formerly were declared as taking 'char' argu-
            ments are now declared as taking 'int' arguments.  This
            prevents getting an excessive number of warnings when pass-
            ing constants to these functions.

            The 'cdecl' keyword was added to the function prototypes to
            prevent problems when compiling with Microsoft's 'fastcall'
            option enabled.  This keyword, as well as the 'near' and
            'far' keywords, may not be compatible with your compiler.
            See MUSTREAD.DOC for more information.

            All the video functions are now prototyped in ANSIDRV.H.
            Before half of them were in ANSIDRV.H and the rest were in
            EXTRA.H.


         TIME OUT FUNCTIONS:

            The time-out functions have been changed to a new version
            that takes a pointer to a 'long' rather than a pointer to a
            TIMEOUT structure.  The new functions are faster and work
            with longer timeouts than the old versions.  Converting to
            the new style consists mainly of changing all occurrences of
            'struct TIMEOUT' in your code to 'long'.