minix/drivers/sensors/sht21/sht21.c

   1 /* Driver for the SHT21 Relative Humidity and Temperature Sensor */
   2
   3 #include <minix/ds.h>
   4 #include <minix/drivers.h>
   5 #include <minix/i2c.h>
   6 #include <minix/i2cdriver.h>
   7 #include <minix/chardriver.h>
   8 #include <minix/log.h>
   9
  10 #include <time.h>
  11
  12 /*
  13  * Device Commands
  14  */
  15
  16 /*
  17  * The trigger commands start a measurement. 'Hold' ties up the bus while the
  18  * measurement is being performed while 'no hold' requires the driver to poll
  19  * the chip until the data is ready. Hold is faster and requires less message
  20  * passing while no hold frees up the bus while the measurement is in progress.
  21  * The worst case conversion times are 85 ms for temperature and 29 ms for
  22  * humidity. Typical conversion times are about 75% of the worst case times.
  23  *
  24  * The driver uses the 'hold' versions of the trigger commands.
  25  */
  26 #define CMD_TRIG_T_HOLD 0xe3
  27 #define CMD_TRIG_RH_HOLD 0xe5
  28 #define CMD_TRIG_T_NOHOLD 0xf3
  29 #define CMD_TRIG_RH_NOHOLD 0xf5
  30
  31 /* Read and write the user register contents */
  32 #define CMD_WR_USR_REG 0xe6
  33 #define CMD_RD_USR_REG 0xe7
  34
  35 /* Resets the chip */
  36 #define CMD_SOFT_RESET 0xfe
  37
  38 /* Status bits included in the measurement need to be masked in calculation */
  39 #define STATUS_BITS_MASK 0x0003
  40
  41 /*
  42  * The user register has some reserved bits that the device changes over
  43  * time. The driver must preserve the value of those bits when writing to
  44  * the user register.
  45  */
  46 #define USR_REG_RESERVED_MASK ((1<<3)|(1<<4)|(1<<5))
  47
  48 /* End of Battery flag is set when the voltage drops below 2.25V. */
  49 #define USR_REG_EOB_MASK (1<<6)
  50
  51 /* When powered up and communicating, the register should have only the
  52  * 'Disable OTP Reload' bit set
  53  */
  54 #define EXPECTED_PWR_UP_TEST_VAL (1<<1)
  55
  56 /* Define some constants for the different sensor types on the chip. */
  57 enum sht21_sensors
  58 { SHT21_T, SHT21_RH };
  59
  60 /* logging - use with log_warn(), log_info(), log_debug(), log_trace(), etc */
  61 static struct log log = {
  62         .name = "sht21",
  63         .log_level = LEVEL_INFO,
  64         .log_func = default_log
  65 };
  66
  67 /* device slave address is fixed at 0x40 */
  68 static i2c_addr_t valid_addrs[2] = {
  69         0x40, 0x00
  70 };
  71
  72 /* Buffer to store output string returned when reading from device file. */
  73 #define BUFFER_LEN 64
  74 char buffer[BUFFER_LEN + 1];
  75
  76 /* the bus that this device is on (counting starting at 1) */
  77 static uint32_t bus;
  78
  79 /* slave address of the device */
  80 static i2c_addr_t address;
  81
  82 /* endpoint for the driver for the bus itself. */
  83 static endpoint_t bus_endpoint;
  84
  85 /* Sampling causes self-heating. To limit the self-heating to < 0.1C, the
  86  * data sheet suggests limiting sampling to 2 samples per second. Since
  87  * the driver samples temperature and relative humidity at the same time,
  88  * it's measure function does at most 1 pair of samples per second. It uses
  89  * this timestamp to see if a measurement was taken less than 1 second ago.
  90  */
  91 static time_t last_sample_time = 0;
  92
  93 /*
  94  * Cache temperature and relative humidity readings. These values are returned
  95  * when the last_sample_time == current_time to keep the chip activity below
  96  * 10% to help prevent self-heating.
  97  */
  98 static int32_t cached_t = 0.0;
  99 static int32_t cached_rh = 0.0;
 100
 101 /*
 102  * An 8-bit CRC is used to validate the readings.
 103  */
 104 #define CRC8_POLYNOMIAL 0x131
 105 #define CRC8_INITIAL_CRC 0x00
 106
 107 /* main driver functions */
 108 static int sht21_init(void);
 109 static int sensor_read(enum sht21_sensors sensor, int32_t * measurement);
 110 static int measure(void);
 111
 112 /* CRC functions */
 113 static uint8_t crc8(uint8_t crc, uint8_t byte);
 114 static int checksum(uint8_t * bytes, int nbytes, uint8_t expected_crc);
 115
 116 /* libchardriver callbacks */
 117 static ssize_t sht21_read(devminor_t minor, u64_t position, endpoint_t endpt,
 118     cp_grant_id_t grant, size_t size, int flags, cdev_id_t id);
 119 static void sht21_other(message * m, int ipc_status);
 120
 121 /* Entry points to this driver from libchardriver. */
 122 static struct chardriver sht21_tab = {
 123         .cdr_read       = sht21_read,
 124         .cdr_other      = sht21_other
 125 };
 126
 127 /*
 128  * Performs a soft reset and reads the contents of the user register to ensure
 129  * that the chip is in a good state and working properly.
 130  */
 131 static int
 132 sht21_init(void)
 133 {
 134         int r;
 135         uint8_t usr_reg_val;
 136
 137         /* Perform a soft-reset */
 138         r = i2creg_raw_write8(bus_endpoint, address, CMD_SOFT_RESET);
 139         if (r != OK) {
 140                 return -1;
 141         }
 142
 143         /* soft reset takes up to 15 ms to complete. */
 144         micro_delay(15000);
 145
 146         log_debug(&log, "Soft Reset Complete\n");
 147
 148         r = i2creg_read8(bus_endpoint, address, CMD_RD_USR_REG, &usr_reg_val);
 149         if (r != OK) {
 150                 return -1;
 151         }
 152
 153         /* Check for End of Battery flag. */
 154         if ((usr_reg_val & USR_REG_EOB_MASK) == USR_REG_EOB_MASK) {
 155                 log_warn(&log, "End of Battery Alarm\n");
 156                 return -1;
 157         }
 158
 159         /* Check that the non-reserved bits are in the default state. */
 160         if ((usr_reg_val & ~USR_REG_RESERVED_MASK) != EXPECTED_PWR_UP_TEST_VAL) {
 161                 log_warn(&log, "USR_REG has non-default values after reset\n");
 162                 log_warn(&log, "Expected 0x%x | Actual 0x%x",
 163                     EXPECTED_PWR_UP_TEST_VAL,
 164                     (usr_reg_val & ~USR_REG_RESERVED_MASK));
 165                 return -1;
 166         }
 167
 168         return OK;
 169 }
 170
 171 /*
 172  * Read from the sensor, check the CRC, convert the ADC value into the final
 173  * representation, and store the result in measurement.
 174  */
 175 static int
 176 sensor_read(enum sht21_sensors sensor, int32_t * measurement)
 177 {
 178         int r;
 179         uint8_t cmd;
 180         uint16_t val;
 181         uint8_t bytes[2];
 182         uint32_t val32;
 183         uint8_t expected_crc;
 184
 185         switch (sensor) {
 186         case SHT21_T:
 187                 cmd = CMD_TRIG_T_HOLD;
 188                 break;
 189         case SHT21_RH:
 190                 cmd = CMD_TRIG_RH_HOLD;
 191                 break;
 192         default:
 193                 log_warn(&log, "sensor_read() called with bad sensor type.\n");
 194                 return -1;
 195         }
 196
 197         if (measurement == NULL) {
 198                 log_warn(&log, "sensor_read() called with NULL pointer\n");
 199                 return -1;
 200         }
 201
 202         r = i2creg_read24(bus_endpoint, address, cmd, &val32);
 203         if (r != OK) {
 204                 log_warn(&log, "sensor_read() failed (r=%d)\n", r);
 205                 return -1;
 206         }
 207
 208         expected_crc = val32 & 0xff;
 209         val = (val32 >> 8) & 0xffff;
 210
 211         bytes[0] = (val >> 8) & 0xff;
 212         bytes[1] = val & 0xff;
 213
 214         r = checksum(bytes, 2, expected_crc);
 215         if (r != OK) {
 216                 return -1;
 217         }
 218
 219         val &= ~STATUS_BITS_MASK;       /* clear status bits */
 220
 221         log_debug(&log, "Read VAL:0x%x CRC:0x%x\n", val, expected_crc);
 222
 223         /* Convert the ADC value to the actual value. */
 224         if (cmd == CMD_TRIG_T_HOLD) {
 225                 *measurement = (int32_t)
 226                     ((-46.85 + ((175.72 / 65536) * ((float) val))) * 1000.0);
 227                 log_debug(&log, "Measured Temperature %d mC\n", *measurement);
 228         } else if (cmd == CMD_TRIG_RH_HOLD) {
 229                 *measurement =
 230                     (int32_t) ((-6.0 +
 231                         ((125.0 / 65536) * ((float) val))) * 1000.0);
 232                 log_debug(&log, "Measured Humidity %d m%%\n", *measurement);
 233         }
 234
 235         return OK;
 236 }
 237
 238 static int
 239 measure(void)
 240 {
 241         int r;
 242         time_t sample_time;
 243         int32_t t, rh;
 244
 245         log_debug(&log, "Taking a measurement...");
 246
 247         sample_time = time(NULL);
 248         if (sample_time == last_sample_time) {
 249                 log_debug(&log, "measure() called too soon, using cache.\n");
 250                 return OK;
 251         }
 252
 253         r = sensor_read(SHT21_T, &t);
 254         if (r != OK) {
 255                 return -1;
 256         }
 257
 258         r = sensor_read(SHT21_RH, &rh);
 259         if (r != OK) {
 260                 return -1;
 261         }
 262
 263         /* save measured values */
 264         cached_t = t;
 265         cached_rh = rh;
 266         last_sample_time = time(NULL);
 267
 268         log_debug(&log, "Measurement completed\n");
 269
 270         return OK;
 271 }
 272
 273 /*
 274  * Return an updated checksum for the given crc and byte.
 275  */
 276 static uint8_t
 277 crc8(uint8_t crc, uint8_t byte)
 278 {
 279         int i;
 280
 281         crc ^= byte;
 282
 283         for (i = 0; i < 8; i++) {
 284
 285                 if ((crc & 0x80) == 0x80) {
 286                         crc = (crc << 1) ^ CRC8_POLYNOMIAL;
 287                 } else {
 288                         crc <<= 1;
 289                 }
 290         }
 291
 292         return crc;
 293 }
 294
 295 /*
 296  * Compute the CRC of an array of bytes and compare it to expected_crc.
 297  * If the computed CRC matches expected_crc, then return OK, otherwise EINVAL.
 298  */
 299 static int
 300 checksum(uint8_t * bytes, int nbytes, uint8_t expected_crc)
 301 {
 302         int i;
 303         uint8_t crc;
 304
 305         crc = CRC8_INITIAL_CRC;
 306
 307         log_debug(&log, "Checking CRC\n");
 308
 309         for (i = 0; i < nbytes; i++) {
 310                 crc = crc8(crc, bytes[i]);
 311         }
 312
 313         if (crc == expected_crc) {
 314                 log_debug(&log, "CRC OK\n");
 315                 return OK;
 316         } else {
 317                 log_warn(&log,
 318                     "Bad CRC -- Computed CRC: 0x%x | Expected CRC: 0x%x\n",
 319                     crc, expected_crc);
 320                 return EINVAL;
 321         }
 322 }
 323
 324 static ssize_t
 325 sht21_read(devminor_t UNUSED(minor), u64_t position, endpoint_t endpt,
 326     cp_grant_id_t grant, size_t size, int UNUSED(flags), cdev_id_t UNUSED(id))
 327 {
 328         u64_t dev_size;
 329         int bytes, r;
 330
 331         r = measure();
 332         if (r != OK) {
 333                 return EIO;
 334         }
 335
 336         memset(buffer, '\0', BUFFER_LEN + 1);
 337         snprintf(buffer, BUFFER_LEN, "%-16s: %d.%03d\n%-16s: %d.%03d\n",
 338             "TEMPERATURE", cached_t / 1000, cached_t % 1000, "HUMIDITY",
 339             cached_rh / 1000, cached_rh % 1000);
 340
 341         log_trace(&log, "%s", buffer);
 342
 343         dev_size = (u64_t)strlen(buffer);
 344         if (position >= dev_size) return 0;
 345         if (position + size > dev_size)
 346                 size = (size_t)(dev_size - position);
 347
 348         r = sys_safecopyto(endpt, grant, 0,
 349             (vir_bytes)(buffer + (size_t)position), size);
 350
 351         return (r != OK) ? r : size;
 352 }
 353
 354 static void
 355 sht21_other(message * m, int ipc_status)
 356 {
 357         int r;
 358
 359         if (is_ipc_notify(ipc_status)) {
 360                 if (m->m_source == DS_PROC_NR) {
 361                         log_debug(&log,
 362                             "bus driver changed state, update endpoint\n");
 363                         i2cdriver_handle_bus_update(&bus_endpoint, bus,
 364                             address);
 365                 }
 366                 return;
 367         }
 368
 369         log_warn(&log, "Invalid message type (0x%x)\n", m->m_type);
 370 }
 371
 372 static int
 373 sef_cb_lu_state_save(int UNUSED(result), int UNUSED(flags))
 374 {
 375         ds_publish_u32("bus", bus, DSF_OVERWRITE);
 376         ds_publish_u32("address", address, DSF_OVERWRITE);
 377         return OK;
 378 }
 379
 380 static int
 381 lu_state_restore(void)
 382 {
 383         /* Restore the state. */
 384         u32_t value;
 385
 386         ds_retrieve_u32("bus", &value);
 387         ds_delete_u32("bus");
 388         bus = (int) value;
 389
 390         ds_retrieve_u32("address", &value);
 391         ds_delete_u32("address");
 392         address = (int) value;
 393
 394         return OK;
 395 }
 396
 397 static int
 398 sef_cb_init(int type, sef_init_info_t * UNUSED(info))
 399 {
 400         int r;
 401
 402         if (type == SEF_INIT_LU) {
 403                 /* Restore the state. */
 404                 lu_state_restore();
 405         }
 406
 407         /* look-up the endpoint for the bus driver */
 408         bus_endpoint = i2cdriver_bus_endpoint(bus);
 409         if (bus_endpoint == 0) {
 410                 log_warn(&log, "Couldn't find bus driver.\n");
 411                 return EXIT_FAILURE;
 412         }
 413
 414         /* claim the device */
 415         r = i2cdriver_reserve_device(bus_endpoint, address);
 416         if (r != OK) {
 417                 log_warn(&log, "Couldn't reserve device 0x%x (r=%d)\n",
 418                     address, r);
 419                 return EXIT_FAILURE;
 420         }
 421
 422         r = sht21_init();
 423         if (r != OK) {
 424                 log_warn(&log, "Device Init Failed\n");
 425                 return EXIT_FAILURE;
 426         }
 427
 428         if (type != SEF_INIT_LU) {
 429
 430                 /* sign up for updates about the i2c bus going down/up */
 431                 r = i2cdriver_subscribe_bus_updates(bus);
 432                 if (r != OK) {
 433                         log_warn(&log, "Couldn't subscribe to bus updates\n");
 434                         return EXIT_FAILURE;
 435                 }
 436
 437                 i2cdriver_announce(bus);
 438                 log_debug(&log, "announced\n");
 439         }
 440
 441         return OK;
 442 }
 443
 444 static void
 445 sef_local_startup(void)
 446 {
 447         /*
 448          * Register init callbacks. Use the same function for all event types
 449          */
 450         sef_setcb_init_fresh(sef_cb_init);
 451         sef_setcb_init_lu(sef_cb_init);
 452         sef_setcb_init_restart(sef_cb_init);
 453
 454         /*
 455          * Register live update callbacks.
 456          */
 457         sef_setcb_lu_state_save(sef_cb_lu_state_save);
 458
 459         /* Let SEF perform startup. */
 460         sef_startup();
 461 }
 462
 463 int
 464 main(int argc, char *argv[])
 465 {
 466         int r;
 467
 468         env_setargs(argc, argv);
 469
 470         r = i2cdriver_env_parse(&bus, &address, valid_addrs);
 471         if (r < 0) {
 472                 log_warn(&log, "Expecting -args 'bus=X address=0xYY'\n");
 473                 log_warn(&log, "Example -args 'bus=1 address=0x40'\n");
 474                 return EXIT_FAILURE;
 475         } else if (r > 0) {
 476                 log_warn(&log,
 477                     "Invalid slave address for device, expecting 0x40\n");
 478                 return EXIT_FAILURE;
 479         }
 480
 481         sef_local_startup();
 482
 483         chardriver_task(&sht21_tab);
 484
 485         return 0;
 486 }