lm70_mediaengine.c

《嵌入式Linux－硬件

/*
 * LM70_mediaengine v1.0 11/05/01
 * www.embeddedlinuxinterfacing.com
 *
 * The original location of this code is
 * http://www.embeddedlinuxinterfacing.com/chapters/10/
 *
 * 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
 */

/*
 * LM70_mediaengine.c is based on procfs_example.c by Erik Mouw.
 * For more information, please see The Linux Kernel Procfs Guide, Erik Mouw
 * http://kernelnewbies.org/documents/kdoc/procfs-guide/lkprocfsguide.html
 */

/* LM70_mediaengine
 * This device driver demonstrates communication with a LM70 temperature
 * sensor using the SA1110 SPI controller. The driver uses polled I/O
 * by checking the SSSR's busy flag instead of using interrupts.
 * The driver creates a /proc directory entry called
 * /proc/trailblazer/temperature. Scripts can read the current temperature
 * from this file.
 */


/*
arm-linux-gcc -O2 -D__KERNEL__ -DMODULE -I/usr/src/arm-linux/include -c LM70_mediaengine.c -o /tftpboot/arm-rootfs/tmp/LM70_mediaengine.o
*/

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/delay.h>

#include <asm/io.h>

#define MODULE_VERSION "1.0"
#define MODULE_NAME    "LM70_mediaengine"


static struct proc_dir_entry  *tb_dir,
                              *temperature_file;


/* see 11.12 Intel StrongARM SA-1110 Microprocessor Developer's Manual */
#define SSP          0x80070000
#define SSCR0_OFFSET 0x60
#define SSCR1_OFFSET 0x64
#define SSDR_OFFSET  0x6C
#define SSSR_OFFSET  0x74

#define SSPLEN       0x78

/* SSP bits */
#define SPP_RNE      0x04
#define SPP_BSY      0x08

static void *ssp_base;

/*
 * function getTemperature
 * This function performs SPI communications with the LM70
 * using programmed I/O (polled mode). Prior to SPI communication,
 * the SA-1110 receive FIFO buffer will be cleared. The getTemperature
 * function will start SPI communication then continuously monitor the
 * SSP busy flag in the SSP Status Register (SSSR). Upon SPI
 * communication completion, the SSP Data Register (SSDR) will contain
 * the 16-bit temperature reading.

 * returns
 * All 16 bits are returned, 11 temperature value bits, 3 1 bits
 * and 2 undefined bits.
 *
 * This routine doesn't perform communication error checking or
 * reporting.
 *
 */
int getTemperature(void)
{
  unsigned char i;
  int temperature, status;

/* need to flush the receive FIFO before we start */
  for (i = 0; i < 16; i++)
  {
    status = readw(ssp_base + SSSR_OFFSET); /* read the status register */
    if ((status & SPP_RNE) == 0) /* is the receive FIFO empty? */
      break;
     temperature = readw(ssp_base + SSDR_OFFSET);
     /* read the receive FIFO to clear out old stuff */
  }

/* start SPI communication, need to feed the transmit FIFO a dummy value */
  writel(0x00, ssp_base + SSDR_OFFSET);

/* now wait until the BSY flag is not set and read the receive FIFO */
  for (i = 0; i < 20; i++)
  {
    status = readw(ssp_base + SSSR_OFFSET); /* read the status register */
    if ((status & SPP_BSY) == 0) /* are we still doing an SPI frame? */
      break;
    udelay(1000); /* wait a little */
  }

  temperature = readw(ssp_base + SSDR_OFFSET); /* read the receive FIFO */

/* for debugging uncomment the next line */
/*  printk("temp:  i is %d, temperature is 0x%04X\n",i, temperature); */

/*
 *  Now we to scale the temperature value. Simply shifting the
 *  bits right doesn't perform the correct operation if the
 *  temperature is below zero. Shifting introduces 0's into the
 *  MSB thus losing the negative sign bit. An integer divide by 32
 *  preserves the sign bit and eliminates the last unused 5 bits
 *
 *  At this point, after the divide by 32. temperature contains
 *  the count of LSB bits where 1 lSB equals 0.25C. An additional
 *  divide by 4 scales temperature in 1 degree increments.
 */
  temperature /= 128; /* 32 * 4 = 128 */

  return temperature;
}


/*
 * function proc_read_temperature
 * This function is called when the user performs a read operation
 * on /proc/trailblazer/temperature. This function fills the page
 * buffer with a temperature in degrees C.
 *
 */
static int proc_read_temperature(char *page, char **start, off_t off, 
                                 int count, int *eof, void *data)
{
  int len, temp;

  temp = getTemperature();
  len = sprintf(page, "%+d\n", temp); /* temp * 9 / 5 + 32 here for F */

  return len;
}

/*
 * function init_LM70_mediaengine
 * This initialization function creates the /proc/trailblazer
 * directory and a temperature entry in it then initializes the
 * LM70 temperature sensor
 *
 */
static int __init init_LM70_mediaengine(void)
{
  unsigned int r;
  int rv = 0;

/* Create the trailblazer /proc entry */
  tb_dir = proc_mkdir("trailblazer", NULL);
  if(tb_dir == NULL) {
    rv = -ENOMEM;
    goto out;
  }
  tb_dir->owner = THIS_MODULE;

/* Create temperature and make it readable by all - 0444 */
  temperature_file = create_proc_entry("temperature", 0444, tb_dir);
  if(temperature_file == NULL) {
    rv = -ENOMEM;
    goto no_temperature;
  }
  temperature_file->data = NULL;
  temperature_file->read_proc = &proc_read_temperature;
  temperature_file->write_proc = NULL;
  temperature_file->owner = THIS_MODULE;

  ssp_base = ioremap_nocache(SSP,SSPLEN);
  printk("ssp_base       = 0x%08X\n",ssp_base);

/*
 * SSCR1 binary value 0000 0000 0000 0000 = 0x0000
 * External Clock Select (ECS),          0 uses internal clock
 * Serial Clock Phase (SPH),             0 adds 1 clock cycle delay
 * Serial Clock Polarity (SPO),          0 holds SC low during idle
 * Loopback Mode (LBM),                  0 disables loopback mode
 * Transmit FIFO Interrupt Enable (TIE), 0 masks interrupt
 * Receive FIFO Interrupt Enable (RIE),  0 masks interrupt
*/
  writel(0x0000, ssp_base + SSCR1_OFFSET);

/*
 * SSCR0 binary value 1111 1111 1000 1111 = 0xFF8F
 * Data Size Select (DSS),               1111 selects 16 bit length
 * Frame Format (FRF),                   00 selects Motorola SPI
 * Synchronous Serial Port Enable (SSE), 1 for enable
 * Serial Clock Rate (SCR),              11111111 selects slowest clock
*/
  writel(0xFF8F, ssp_base + SSCR0_OFFSET);

/* read the registers and printout results */
  r = readl(ssp_base + SSCR1_OFFSET);
  printk("SSCR1          = 0x%04X\n",r);
  r = readl(ssp_base + SSCR0_OFFSET);
  printk("SSCR0          = 0x%04X\n",r);

/* everything initialized */
  printk(KERN_INFO "%s %s initialized\n", MODULE_NAME, MODULE_VERSION);
  return 0;

no_temperature:
 remove_proc_entry("trailblazer", NULL);
out:
 return rv;
}

/*
 * function cleanup_LM70_mediaengine
 * This clean function powers down the sensor and removes
 * the /proc/trailblazer directory and the temperature entry.
 */
static void __exit cleanup_LM70_mediaengine(void)
{
  iounmap(ssp_base);

  remove_proc_entry("temperature", tb_dir);
  remove_proc_entry("trailblazer", NULL);

  printk(KERN_INFO "%s %s removed\n", MODULE_NAME, MODULE_VERSION);
}


module_init(init_LM70_mediaengine);
module_exit(cleanup_LM70_mediaengine);

MODULE_AUTHOR("Craig Hollabaugh");
MODULE_DESCRIPTION("Trailblazer LM70_mediaengine");

EXPORT_NO_SYMBOLS;