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linux下的RS485的驱动 值得一看

ul_drv - uLan RS-485 communication driver

Copyright (C) 1999 Pavel Pisa  ([e-mail])

uLan provides 9-bit message oriented communication protocol,
which is transfered over RS-485 link. Characters are transfered
same way as for RS-232 asynchronous transfer except parity
bit, which is used to distinguish between data characters
and protocol control information. Physical layer consist
of one twisted pair of leads and RS-485 transceivers.

ul_drv is Linux device driver designed to access uLan network. 
Latest versions of the ul_drv can be compiled from same 
source into Windows NT KMD driver too (try to use ul_drv.mak).
Today supported hardware is i82510 RS-485 card or simple
active converter dongle for standard PC RS-232 ports.
This version of driver was compiled and tested with 
Linux 2.2.4 kernel. Header file k_compat.h should enable
compilation for most of 2.0.xx, 2.1.xx and 2.2.xx kernels,
but tweaking of k_compat.h may be necessary for some
2.1.xx kernel versions.

Makefile is link to Makefile-mod to compile driver with
your kernel configuration. Makefile-mod expect, that
kernel sources are in "/usr/src/linux" directory
and that kernel sources and its configuration 
are of same version as current running kernel.
Enter next command in ul_drv directory to compile and
install the module

    make install

Module is installed into "/lib/modules/x.y.z/misc" directory.

Driver can control up to four devices, but only check
for 0x3e8 port number is default behavior after "insmod ul_drv".
Because of driver controls same hardware as Linux serial
driver, it is necessary to disable default kernel driver
for same port in case of conflict. It can be done for example by

    setserial /dev/ttyS2 uart none

Port numbers and others parameters can be defined by module 
parameters. To access driver from programs special character
device files must be created. Suggested names are

    mknod /dev/ulan0 c 248 0
    mknod /dev/ulan1 c 248 1
    ln -sf /dev/ulan0 /dev/ulan

"/dev/ulan" is default name for client programs.
Major number 248 is in experimental range and will
be changed in future. Number is defined in ul_hdep.h.
If defined as zero, dynamic number is assigned after insmod.

ul_drv module parameters

  port=<iop>{,<iop> ...}
	up to four IO port numbers separated by comas
        for up to four uLan devices

  irq=<int>{,<int> ...}
	select for every defined device corresponding
	IRQ number. Value 0 means autoprobe.

  baud=<spd>{,<spd> ...}
	defines transfer baud-rate for every device
	default value is 9600

  my_adr=<adr>{,<adr> ...}
	address of every computer interface as seen
	from uLan network 
	range is from 1 to 64
	default value is 2 for all interfaces


Bellow are example parameters for dongle converter plugged
to regular COM2 port.

    setserial /dev/ttyS1 uart none
    insmod ul_drv port=0x2f8 irq=3 baud=9600 my_adr=2

Add next lines to /etc/modules.conf to enable on-demand
module loading

    alias    char-major-248 ul_drv
    options    ul_drv port=0x2f8 irq=3 baud=9600 my_adr=2
    pre-install ul_drv /sbin/setserial /dev/ttyS1 uart none