drivers/misc/bmp085.c

   1 /*  Copyright (c) 2010  Christoph Mair <christoph.mair@gmail.com>
   2
   3     This driver supports the bmp085 digital barometric pressure
   4     and temperature sensor from Bosch Sensortec. The datasheet
   5     is available from their website:
   6     http://www.bosch-sensortec.com/content/language1/downloads/BST-BMP085-DS000-05.pdf
   7
   8     A pressure measurement is issued by reading from pressure0_input.
   9     The return value ranges from 30000 to 110000 pascal with a resulution
  10     of 1 pascal (0.01 millibar) which enables measurements from 9000m above
  11     to 500m below sea level.
  12
  13     The temperature can be read from temp0_input. Values range from
  14     -400 to 850 representing the ambient temperature in degree celsius
  15     multiplied by 10.The resolution is 0.1 celsius.
  16
  17     Because ambient pressure is temperature dependent, a temperature
  18     measurement will be executed automatically even if the user is reading
  19     from pressure0_input. This happens if the last temperature measurement
  20     has been executed more then one second ago.
  21
  22     To decrease RMS noise from pressure measurements, the bmp085 can
  23     autonomously calculate the average of up to eight samples. This is
  24     set up by writing to the oversampling sysfs file. Accepted values
  25     are 0, 1, 2 and 3. 2^x when x is the value written to this file
  26     specifies the number of samples used to calculate the ambient pressure.
  27     RMS noise is specified with six pascal (without averaging) and decreases
  28     down to 3 pascal when using an oversampling setting of 3.
  29
  30     This program is free software; you can redistribute it and/or modify
  31     it under the terms of the GNU General Public License as published by
  32     the Free Software Foundation; either version 2 of the License, or
  33     (at your option) any later version.
  34
  35     This program is distributed in the hope that it will be useful,
  36     but WITHOUT ANY WARRANTY; without even the implied warranty of
  37     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  38     GNU General Public License for more details.
  39
  40     You should have received a copy of the GNU General Public License
  41     along with this program; if not, write to the Free Software
  42     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  43 */
  44
  45
  46 #include <linux/module.h>
  47 #include <linux/init.h>
  48 #include <linux/i2c.h>
  49 #include <linux/slab.h>
  50 #include <linux/delay.h>
  51
  52
  53 #define BMP085_I2C_ADDRESS              0x77
  54 #define BMP085_CHIP_ID                  0x55
  55
  56 #define BMP085_CALIBRATION_DATA_START   0xAA
  57 #define BMP085_CALIBRATION_DATA_LENGTH  11      /* 16 bit values */
  58 #define BMP085_CHIP_ID_REG              0xD0
  59 #define BMP085_VERSION_REG              0xD1
  60 #define BMP085_CTRL_REG                 0xF4
  61 #define BMP085_TEMP_MEASUREMENT         0x2E
  62 #define BMP085_PRESSURE_MEASUREMENT     0x34
  63 #define BMP085_CONVERSION_REGISTER_MSB  0xF6
  64 #define BMP085_CONVERSION_REGISTER_LSB  0xF7
  65 #define BMP085_CONVERSION_REGISTER_XLSB 0xF8
  66 #define BMP085_TEMP_CONVERSION_TIME     5
  67
  68 #define BMP085_CLIENT_NAME              "bmp085"
  69
  70
  71 static const unsigned short normal_i2c[] = { BMP085_I2C_ADDRESS,
  72                                                         I2C_CLIENT_END };
  73
  74 struct bmp085_calibration_data {
  75         s16 AC1, AC2, AC3;
  76         u16 AC4, AC5, AC6;
  77         s16 B1, B2;
  78         s16 MB, MC, MD;
  79 };
  80
  81
  82 /* Each client has this additional data */
  83 struct bmp085_data {
  84         struct i2c_client *client;
  85         struct mutex lock;
  86         struct bmp085_calibration_data calibration;
  87         u32 raw_temperature;
  88         u32 raw_pressure;
  89         unsigned char oversampling_setting;
  90         unsigned long last_temp_measurement;
  91         s32 b6; /* calculated temperature correction coefficient */
  92 };
  93
  94
  95 static s32 bmp085_read_calibration_data(struct i2c_client *client)
  96 {
  97         u16 tmp[BMP085_CALIBRATION_DATA_LENGTH];
  98         struct bmp085_data *data = i2c_get_clientdata(client);
  99         struct bmp085_calibration_data *cali = &(data->calibration);
 100         s32 status = i2c_smbus_read_i2c_block_data(client,
 101                                 BMP085_CALIBRATION_DATA_START,
 102                                 BMP085_CALIBRATION_DATA_LENGTH*sizeof(u16),
 103                                 (u8 *)tmp);
 104         if (status < 0)
 105                 return status;
 106
 107         if (status != BMP085_CALIBRATION_DATA_LENGTH*sizeof(u16))
 108                 return -EIO;
 109
 110         cali->AC1 =  be16_to_cpu(tmp[0]);
 111         cali->AC2 =  be16_to_cpu(tmp[1]);
 112         cali->AC3 =  be16_to_cpu(tmp[2]);
 113         cali->AC4 =  be16_to_cpu(tmp[3]);
 114         cali->AC5 =  be16_to_cpu(tmp[4]);
 115         cali->AC6 = be16_to_cpu(tmp[5]);
 116         cali->B1 = be16_to_cpu(tmp[6]);
 117         cali->B2 = be16_to_cpu(tmp[7]);
 118         cali->MB = be16_to_cpu(tmp[8]);
 119         cali->MC = be16_to_cpu(tmp[9]);
 120         cali->MD = be16_to_cpu(tmp[10]);
 121         return 0;
 122 }
 123
 124
 125 static s32 bmp085_update_raw_temperature(struct bmp085_data *data)
 126 {
 127         u16 tmp;
 128         s32 status;
 129
 130         mutex_lock(&data->lock);
 131         status = i2c_smbus_write_byte_data(data->client, BMP085_CTRL_REG,
 132                                                 BMP085_TEMP_MEASUREMENT);
 133         if (status != 0) {
 134                 dev_err(&data->client->dev,
 135                         "Error while requesting temperature measurement.\n");
 136                 goto exit;
 137         }
 138         msleep(BMP085_TEMP_CONVERSION_TIME);
 139
 140         status = i2c_smbus_read_i2c_block_data(data->client,
 141                 BMP085_CONVERSION_REGISTER_MSB, sizeof(tmp), (u8 *)&tmp);
 142         if (status < 0)
 143                 goto exit;
 144         if (status != sizeof(tmp)) {
 145                 dev_err(&data->client->dev,
 146                         "Error while reading temperature measurement result\n");
 147                 status = -EIO;
 148                 goto exit;
 149         }
 150         data->raw_temperature = be16_to_cpu(tmp);
 151         data->last_temp_measurement = jiffies;
 152         status = 0;     /* everything ok, return 0 */
 153
 154 exit:
 155         mutex_unlock(&data->lock);
 156         return status;
 157 }
 158
 159 static s32 bmp085_update_raw_pressure(struct bmp085_data *data)
 160 {
 161         u32 tmp = 0;
 162         s32 status;
 163
 164         mutex_lock(&data->lock);
 165         status = i2c_smbus_write_byte_data(data->client, BMP085_CTRL_REG,
 166                 BMP085_PRESSURE_MEASUREMENT + (data->oversampling_setting<<6));
 167         if (status != 0) {
 168                 dev_err(&data->client->dev,
 169                         "Error while requesting pressure measurement.\n");
 170                 goto exit;
 171         }
 172
 173         /* wait for the end of conversion */
 174         msleep(2+(3 << data->oversampling_setting));
 175
 176         /* copy data into a u32 (4 bytes), but skip the first byte. */
 177         status = i2c_smbus_read_i2c_block_data(data->client,
 178                         BMP085_CONVERSION_REGISTER_MSB, 3, ((u8 *)&tmp)+1);
 179         if (status < 0)
 180                 goto exit;
 181         if (status != 3) {
 182                 dev_err(&data->client->dev,
 183                         "Error while reading pressure measurement results\n");
 184                 status = -EIO;
 185                 goto exit;
 186         }
 187         data->raw_pressure = be32_to_cpu((tmp));
 188         data->raw_pressure >>= (8-data->oversampling_setting);
 189         status = 0;     /* everything ok, return 0 */
 190
 191 exit:
 192         mutex_unlock(&data->lock);
 193         return status;
 194 }
 195
 196
 197 /*
 198  * This function starts the temperature measurement and returns the value
 199  * in tenth of a degree celsius.
 200  */
 201 static s32 bmp085_get_temperature(struct bmp085_data *data, int *temperature)
 202 {
 203         struct bmp085_calibration_data *cali = &data->calibration;
 204         long x1, x2;
 205         int status;
 206
 207         status = bmp085_update_raw_temperature(data);
 208         if (status != 0)
 209                 goto exit;
 210
 211         x1 = ((data->raw_temperature - cali->AC6) * cali->AC5) >> 15;
 212         x2 = (cali->MC << 11) / (x1 + cali->MD);
 213         data->b6 = x1 + x2 - 4000;
 214         /* if NULL just update b6. Used for pressure only measurements */
 215         if (temperature != NULL)
 216                 *temperature = (x1+x2+8) >> 4;
 217
 218 exit:
 219         return status;
 220 }
 221
 222 /*
 223  * This function starts the pressure measurement and returns the value
 224  * in millibar. Since the pressure depends on the ambient temperature,
 225  * a temperature measurement is executed if the last known value is older
 226  * than one second.
 227  */
 228 static s32 bmp085_get_pressure(struct bmp085_data *data, int *pressure)
 229 {
 230         struct bmp085_calibration_data *cali = &data->calibration;
 231         s32 x1, x2, x3, b3;
 232         u32 b4, b7;
 233         s32 p;
 234         int status;
 235
 236         /* alt least every second force an update of the ambient temperature */
 237         if (data->last_temp_measurement == 0 ||
 238                         time_is_before_jiffies(data->last_temp_measurement + 1*HZ)) {
 239                 status = bmp085_get_temperature(data, NULL);
 240                 if (status != 0)
 241                         goto exit;
 242         }
 243
 244         status = bmp085_update_raw_pressure(data);
 245         if (status != 0)
 246                 goto exit;
 247
 248         x1 = (data->b6 * data->b6) >> 12;
 249         x1 *= cali->B2;
 250         x1 >>= 11;
 251
 252         x2 = cali->AC2 * data->b6;
 253         x2 >>= 11;
 254
 255         x3 = x1 + x2;
 256
 257         b3 = (((((s32)cali->AC1) * 4 + x3) << data->oversampling_setting) + 2);
 258         b3 >>= 2;
 259
 260         x1 = (cali->AC3 * data->b6) >> 13;
 261         x2 = (cali->B1 * ((data->b6 * data->b6) >> 12)) >> 16;
 262         x3 = (x1 + x2 + 2) >> 2;
 263         b4 = (cali->AC4 * (u32)(x3 + 32768)) >> 15;
 264
 265         b7 = ((u32)data->raw_pressure - b3) *
 266                                         (50000 >> data->oversampling_setting);
 267         p = ((b7 < 0x80000000) ? ((b7 << 1) / b4) : ((b7 / b4) * 2));
 268
 269         x1 = p >> 8;
 270         x1 *= x1;
 271         x1 = (x1 * 3038) >> 16;
 272         x2 = (-7357 * p) >> 16;
 273         p += (x1 + x2 + 3791) >> 4;
 274
 275         *pressure = p;
 276
 277 exit:
 278         return status;
 279 }
 280
 281 /*
 282  * This function sets the chip-internal oversampling. Valid values are 0..3.
 283  * The chip will use 2^oversampling samples for internal averaging.
 284  * This influences the measurement time and the accuracy; larger values
 285  * increase both. The datasheet gives on overview on how measurement time,
 286  * accuracy and noise correlate.
 287  */
 288 static void bmp085_set_oversampling(struct bmp085_data *data,
 289                                                 unsigned char oversampling)
 290 {
 291         if (oversampling > 3)
 292                 oversampling = 3;
 293         data->oversampling_setting = oversampling;
 294 }
 295
 296 /*
 297  * Returns the currently selected oversampling. Range: 0..3
 298  */
 299 static unsigned char bmp085_get_oversampling(struct bmp085_data *data)
 300 {
 301         return data->oversampling_setting;
 302 }
 303
 304 /* sysfs callbacks */
 305 static ssize_t set_oversampling(struct device *dev,
 306                                 struct device_attribute *attr,
 307                                 const char *buf, size_t count)
 308 {
 309         struct i2c_client *client = to_i2c_client(dev);
 310         struct bmp085_data *data = i2c_get_clientdata(client);
 311         unsigned long oversampling;
 312         int success = strict_strtoul(buf, 10, &oversampling);
 313         if (success == 0) {
 314                 bmp085_set_oversampling(data, oversampling);
 315                 return count;
 316         }
 317         return success;
 318 }
 319
 320 static ssize_t show_oversampling(struct device *dev,
 321                                  struct device_attribute *attr, char *buf)
 322 {
 323         struct i2c_client *client = to_i2c_client(dev);
 324         struct bmp085_data *data = i2c_get_clientdata(client);
 325         return sprintf(buf, "%u\n", bmp085_get_oversampling(data));
 326 }
 327 static DEVICE_ATTR(oversampling, S_IWUSR | S_IRUGO,
 328                                         show_oversampling, set_oversampling);
 329
 330
 331 static ssize_t show_temperature(struct device *dev,
 332                                 struct device_attribute *attr, char *buf)
 333 {
 334         int temperature;
 335         int status;
 336         struct i2c_client *client = to_i2c_client(dev);
 337         struct bmp085_data *data = i2c_get_clientdata(client);
 338
 339         status = bmp085_get_temperature(data, &temperature);
 340         if (status != 0)
 341                 return status;
 342         else
 343                 return sprintf(buf, "%d\n", temperature);
 344 }
 345 static DEVICE_ATTR(temp0_input, S_IRUGO, show_temperature, NULL);
 346
 347
 348 static ssize_t show_pressure(struct device *dev,
 349                              struct device_attribute *attr, char *buf)
 350 {
 351         int pressure;
 352         int status;
 353         struct i2c_client *client = to_i2c_client(dev);
 354         struct bmp085_data *data = i2c_get_clientdata(client);
 355
 356         status = bmp085_get_pressure(data, &pressure);
 357         if (status != 0)
 358                 return status;
 359         else
 360                 return sprintf(buf, "%d\n", pressure);
 361 }
 362 static DEVICE_ATTR(pressure0_input, S_IRUGO, show_pressure, NULL);
 363
 364
 365 static struct attribute *bmp085_attributes[] = {
 366         &dev_attr_temp0_input.attr,
 367         &dev_attr_pressure0_input.attr,
 368         &dev_attr_oversampling.attr,
 369         NULL
 370 };
 371
 372 static const struct attribute_group bmp085_attr_group = {
 373         .attrs = bmp085_attributes,
 374 };
 375
 376 static int bmp085_detect(struct i2c_client *client, struct i2c_board_info *info)
 377 {
 378         if (client->addr != BMP085_I2C_ADDRESS)
 379                 return -ENODEV;
 380
 381         if (i2c_smbus_read_byte_data(client, BMP085_CHIP_ID_REG) != BMP085_CHIP_ID)
 382                 return -ENODEV;
 383
 384         return 0;
 385 }
 386
 387 static int bmp085_init_client(struct i2c_client *client)
 388 {
 389         unsigned char version;
 390         int status;
 391         struct bmp085_data *data = i2c_get_clientdata(client);
 392         data->client = client;
 393         status = bmp085_read_calibration_data(client);
 394         if (status != 0)
 395                 goto exit;
 396         version = i2c_smbus_read_byte_data(client, BMP085_VERSION_REG);
 397         data->last_temp_measurement = 0;
 398         data->oversampling_setting = 3;
 399         mutex_init(&data->lock);
 400         dev_info(&data->client->dev, "BMP085 ver. %d.%d found.\n",
 401                         (version & 0x0F), (version & 0xF0) >> 4);
 402 exit:
 403         return status;
 404 }
 405
 406 static int __devinit bmp085_probe(struct i2c_client *client,
 407                          const struct i2c_device_id *id)
 408 {
 409         struct bmp085_data *data;
 410         int err = 0;
 411
 412         data = kzalloc(sizeof(struct bmp085_data), GFP_KERNEL);
 413         if (!data) {
 414                 err = -ENOMEM;
 415                 goto exit;
 416         }
 417
 418         /* default settings after POR */
 419         data->oversampling_setting = 0x00;
 420
 421         i2c_set_clientdata(client, data);
 422
 423         /* Initialize the BMP085 chip */
 424         err = bmp085_init_client(client);
 425         if (err != 0)
 426                 goto exit_free;
 427
 428         /* Register sysfs hooks */
 429         err = sysfs_create_group(&client->dev.kobj, &bmp085_attr_group);
 430         if (err)
 431                 goto exit_free;
 432
 433         dev_info(&data->client->dev, "Successfully initialized bmp085!\n");
 434         goto exit;
 435
 436 exit_free:
 437         kfree(data);
 438 exit:
 439         return err;
 440 }
 441
 442 static int __devexit bmp085_remove(struct i2c_client *client)
 443 {
 444         sysfs_remove_group(&client->dev.kobj, &bmp085_attr_group);
 445         kfree(i2c_get_clientdata(client));
 446         return 0;
 447 }
 448
 449 static const struct i2c_device_id bmp085_id[] = {
 450         { "bmp085", 0 },
 451         { }
 452 };
 453 MODULE_DEVICE_TABLE(i2c, bmp085_id);
 454
 455 static struct i2c_driver bmp085_driver = {
 456         .driver = {
 457                 .owner = THIS_MODULE,
 458                 .name   = "bmp085"
 459         },
 460         .id_table       = bmp085_id,
 461         .probe          = bmp085_probe,
 462         .remove         = __devexit_p(bmp085_remove),
 463
 464         .detect         = bmp085_detect,
 465         .address_list   = normal_i2c
 466 };
 467
 468 module_i2c_driver(bmp085_driver);
 469
 470 MODULE_AUTHOR("Christoph Mair <christoph.mair@gmail.com");
 471 MODULE_DESCRIPTION("BMP085 driver");
 472 MODULE_LICENSE("GPL");