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<H2><A NAME="s1">1. Device Driver Support</A> </H2>
<P>$Id: rt_com-1.html,v 1.1 1999/07/31 16:20:46 baraban Exp $
<H2><A NAME="ss1.1">1.1 rt_com - serial port driver</A>
</H2>
<P>author: Jochen Küpper <jochen@uni-duesseldorf.de>
<P>last changed: $Date: 1999/07/31 16:20:46 $
<P>This manual is intended to describe <CODE>rt_com</CODE> version 0.3, but is not fully updated
to match that version yet. The interface should be right, though.
<H3>Introduction </H3>
<P>This chapter of the manual describes the <CODE>rt_com</CODE> kernel module. That module provides
a reasonable easy software interface (driver) to the standard serial ports of the
PCs. There are a small number of user functions that provide an interface to the
port, as well as several functions internally used to communicate with the hardware.
<P>
<H3>Installation </H3>
<P>The rt_com package should contain the source code (<CODE>rt_com.h</CODE>, <CODE>rt_com.c</CODE>, <CODE>rt_comP.h</CODE>),
makefiles (<CODE>Makefile.am</CODE>, <CODE>Makefile.standalone</CODE>), some informational files (<CODE>COPYING</CODE>,
<CODE>License</CODE>, <CODE>README</CODE>) and this documentation in various formats. The master file is <CODE>rt_com.lyx</CODE>,
there are also html and Postscript versions of it available.
<P>The module works with RT-Linux v1 and v2. In order to run it on an v1 system
(Linux kernel 2.0.x) you need to define <CODE>RTLINUX_V1</CODE> at compile time.
<H3>Interface functions </H3>
<H3>Setting up a serial port </H3>
<P>This is to set up the port for use by your module by providing some initialization
data. The function is declared as
<P>
<HR>
<PRE>
void rt_com_setup( unsigned int com, unsigned baud, unsigned parity, unsigned stopbits, unsigned wordlength)
</PRE>
<HR>
<P>where com is the entry number from the<CODE> rt_com_table</CODE> (see paragraph
<A HREF="#rt_com_table">rt_com_table</A> ), baud
is the Baud rate the port shall be operated at, parity determines the parity policy
to use (possible values are <CODE>RT_COM_PARITY_EVEN</CODE>, <CODE>RT_COM_PARITY_NONE</CODE>, <CODE>RT_COM_PARITY_ODD</CODE>
- these are defined in <CODE>rt_com.h</CODE>), stopbits and wordlength are self explanatory and
take the immediate value these flags shall be set at.
<H3>Writing data to a port </H3>
<P>To write data to a port you need to call the function<CODE> rt_com_write</CODE>, which is
declared as
<P>
<HR>
<PRE>
void rt_com_write( unsigned int com, char *buf, int cnt )
</PRE>
<HR>
<P>where com is the entry number from the <CODE>rt_com_table</CODE> (see paragraph
<A HREF="#rt_com_table">rt_com_table</A> ), buf is
the memory address of the data to write to the port, cnt is the number of bytes
that shall be written.
<H3>Reading data from a port </H3>
<P>To read data from a port you need to call the function rt_com_read, which is
declared as
<P>
<HR>
<PRE>
int rt_com_read( unsigned int com, char *buf, int cnt )
</PRE>
<HR>
<P>where com is the entry number from the<CODE> rt_com_table</CODE> (see paragraph
<A HREF="#rt_com_table">rt_com_table</A> ), buf is
the memory address the data read shall be put in, cnt is the maximum number of bytes
that shall be read. The function returns the number of bytes that really have been
read.
<H3>Internals </H3>
<H3><A NAME="init_module"></A> Loading the module into memory </H3>
<P>When the module gets loaded it requests the port memory and registers the interrupt
service routine (ISR) for each member of the rt_com_table (see paragraph
<A HREF="#rt_com_table">rt_com_table</A>). Moreover
it initializes all ports.
<P>On success it reports the loading of the module, otherwise it releases all resources,
reports the failure and exits without the module beeing loaded.
<H3>Removing the module </H3>
<P>Before the module is removed from memory, the function cleanup_module frees
all allocated resources.
<H3>Data Structures </H3>
<H3><A NAME="rt_buf_struct"></A> rt_buf_struct </H3>
<P>Structure to implement software FIFOs. Used for buffering of the data that needs
to be written to the port and data read from hardware that needs to be read by the
user. The FIFO size is given by the define <CODE>RT_COM_BUF_SIZ</CODE>; it has to be a power
of two.
<H3>rt_com_struct </H3>
<P>Defines the hardware parameter of one serial port. The members of this structure
are a magic number (not used yet), the base rate of the port (115200 for standard
ports), the port number, the interrupt number (IRQ) of the port, the flags set for
this port, the ISR (see paragraph
<A HREF="#init_module">init_module</A>) the type and a copy of the IER register. Moreover
it contains two FIFOs as defined by the <CODE>rt_buf_struc</CODE> (see paragraph
<A HREF="#rt_buf_struct">rt_buf_struct</A>), one for reading
from the port and one for writing to it, respectively.
<H3><A NAME="rt_com_table"></A> rt_com_table </H3>
<P>This array holds a rt_com_struct for each serial port to be handled by the module.
<H3>Availability </H3>
<P>The package is available at the
<A HREF="http://www-public.rz.uni-duesseldorf.de/~jochen/computer/software/rt_com/">rt_com homepage</A> and the
<A HREF="http://www.rtlinux.org">RT-Linux homepage</A>.
<H3>Bugs </H3>
<P>Please report bugs to
<A HREF="mailto:jochen@uni-duesseldorf.de">Jochen Küpper</A> and the
<A HREF="mailto:rtl@rtlinux.cs.nmt.edu">RT-Linux maiing list</A>.
<P>There are no known bugs right now.
<H3>Acknowledgment </H3>
<P>Thanks to Jens Michaelsen for providing his code.
<HR>
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