snowmakingcontrol.c.txt

这是《嵌入式linux－硬件、软件与接口》一书对应的所有linux方面实例的源代码

/*
 * snowmakingcontrol v0.1 9/25/01
 * www.embeddedlinuxinterfacing.com
 *
 * The original location of this code is
 * http://www.embeddedlinuxinterfacing.com/chapters/07/snowmakingcontrol.c
 *
 *
 * Copyright (C) 2001 by Craig Hollabaugh
 *
 * This program is free software; you can redistribute it and/or modify 
 * it under the terms of the GNU Library General Public License as 
 * published by the Free Software Foundation; either version 2 of the 
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of 
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public 
 * License along with this program; if not, write to the 
 * Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

/* snowmakingcontrol
 * snowmakingcontrol uses outb system calls to control an interface
 * circuit connected the PC parallel printer port. The port's 
 * control port drives the interface circuit's output latch signals.
 */

/*
remember to compile with -O2 for proper inb/outb macro expansion
gcc -O2 -o snowmakingcontrol snowmakingcontrol.c
*/


#include <asm/io.h>

#define SPPDATAPORT     0x378
#define SPPSTATUSPORT  (SPPDATAPORT + 1)
#define SPPCONTROLPORT (SPPDATAPORT + 2)

/* these are the control port bit defs */
#define OUTPUTENABLE 0x02
#define OUTPUTLATCH  0x04
#define INPUTENABLE  0x08
#define SPPPORTREAD  0x20

int main(int argc, char *argv[])
{
/* get permission from the OS to use the 
 * data, status and control ports*/
  if (ioperm(SPPDATAPORT, 3, 1))
  {
    perror("ioperm");
    exit(1);
  }

/* Use OUTPUTENABLE to keep output latch enabled */
  outb(OUTPUTENABLE               ,SPPCONTROLPORT); 

/* put the first char of command line argument 1 on the data bus */
  outb(argv[1][0],SPPDATAPORT);

/* assert OUTPUTLATCH, this latches the data bus to the latch's 
 * outputs, driving the output module rack */
  outb(OUTPUTENABLE | OUTPUTLATCH ,SPPCONTROLPORT); //latch data

/* Use OUTPUTENABLE to keep output latch enabled */
  outb(OUTPUTENABLE               ,SPPCONTROLPORT); 

/* let OS know we're done with the port */
  if (ioperm(SPPDATAPORT, 3, 0))
  {
    perror("ioperm");
    exit(1);
  }
}