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=============================================================================
                      MARK REJHON'S 16550 UART EMULATOR
=============================================================================

	This directory contains Mark Rejhon's 16550A UART emulation code.

	Please send bug reports related to DOSEMU serial to either
	<mdrejhon@magi.com> or <ag115@freenet.carleton.ca>

	The files in this subdirectory are:
	   Makefile		- The Makefile for this subdir.
	   README.serial	- This file that you are reading now.
	   ser_init.c		- Serial initialization code.
	   ser_ports.c		- Serial Port I/O emulation code.
	   ser_irq.c		- Serial Interrupts emulation code.
	   ser_defs.h		- Include file for above files only.
	   ../include/serial.h	- General include file for all DOSEMU code.

	Redistribution of these files is permitted under the terms of the 
	GNU Public License (GPL).  See end of this file for more information.
 



PROGRAMMING INFORMATION
~~~~~~~~~~~~~~~~~~~~~~~
	Information on a 16550 is based on information from 
	HELPPC.EXE 2.1 and results from National Semiconductor's
	COMTEST.EXE diagnostics program.  This code aims to emulate 
	a 16550A as accurately as possible, using just reasonably 
	POSIX.2 compilant code.  In some cases, this code does a 
	better job than OS/2 serial emulation (in non-direct mode) 
	done by its COM.SYS driver!  There may be about 100 kilobytes
	of source code, but nearly 50% of this size are comments!

	This 16550A emulator never even touches the real serial ports,
	it merely traps port writes, and does the I/O via file functions
	on a device in /dev.  Interrupts are also simulated as necessary.

	One of the most important things to know before programming
	this serial code, is to understand how the com[] array works.  

	Most of the serial variables are stored in the com[] array.
	The com[] array is a structure in itself.   Take a look at the
	'serial_t' struct declaration in the ../include/serial.h module 
	for more info about this.  Only the most commonly referenced 
	global variables are listed here:

	config.num_ser         Number of serial ports active.
	com[x].base_port       The base port address of emulated serial port.
	com[x].real_comport    The COM port number.
	com[x].interrupt       The PIC interrupt level (based on IRQ number)
	com[x].mouse           Flag  mouse (to enable extended features)
	com[x].fd              File descriptor for port device 
	com[x].dev[]           Filename of port port device
	com[x].dev_locked      Flag whether device has been locked

	The arbritary example variable 'x' in com[x] can have a minimum 
	value of 0 and a maximum value of (config.numser - 1).  There 
	can be no gaps for the value 'x', even though gaps between actual 
	COM ports are permitted.  It is strongly noted that the 'x' does 
	not equal the COM port number.  This example code illustrates 
	the fact, and how the com[x] array works:

	  for (i = 0; i < config.numser; i++)
	    s_printf("COM port number %d has a base address of %x", 
	             com[i].real_comport, com[i].base_port);




DEBUGGING HELP
~~~~~~~~~~~~~~
	If you require heavy debugging output for serial operations,
	please take a look in ./ser_defs.h for the following defines:

	SER_DEBUG_MAIN   (0 or 1)
	  - extra debug output on the most critical information.

	SER_DEBUG_HEAVY   (0 or 1)
	  - super-heavy extra debug output, including all ports reads 
	    and writes, and every character received and transmitted!

	SER_DEBUG_INTERRUPT   (0 or 1)
	  - additional debug output related to serial interrupt code,
	    including flagging serial interrupts, or PIC-driven code.




COPYRIGHTS
~~~~~~~~~~
	Most of the code in the DOSEMU 'serial' subdirectory is:
	Copyright (C) 1995 by Mark D. Rejhon <mdrejhon@magi.com>
	with the following exceptions:

	Lock-file functions were derived from Taylor UUCP:
	Copyright (C) 1991, 1992 Ian Lance Taylor
	Uri Blumenthal <uri@watson.ibm.com> (C) 1994
	Paul Cadach, <paul@paul.east.alma-ata.su> (C) 1994

	UART definitions were derived from /linux/include/linux/serial.h
	Copyright (C) 1992 by Theodore Ts'o.

	All of this serial code is free software; you can redistribute it
	and/or modify it under the terms of the GNU General Public License
	as published by the Free Software Foundation; either version 2 of 
	the License, or (at your option) any later version.

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