src/hardware/fluke-dmm/protocol.c

   1 /*
   2  * This file is part of the libsigrok project.
   3  *
   4  * Copyright (C) 2012 Bert Vermeulen <bert@biot.com>
   5  *
   6  * This program is free software: you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation, either version 3 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <config.h>
  21 #include <stdlib.h>
  22 #include <math.h>
  23 #include <string.h>
  24 #include <glib.h>
  25 #include <libsigrok/libsigrok.h>
  26 #include "libsigrok-internal.h"
  27 #include "protocol.h"
  28
  29 static struct sr_datafeed_analog *handle_qm_18x(const struct sr_dev_inst *sdi,
  30                 char **tokens)
  31 {
  32         struct sr_datafeed_analog *analog;
  33         struct sr_analog_encoding encoding;
  34         struct sr_analog_meaning meaning;
  35         struct sr_analog_spec spec;
  36         float fvalue;
  37         char *e, *u;
  38         gboolean is_oor;
  39
  40         if (strcmp(tokens[0], "QM") || !tokens[1])
  41                 return NULL;
  42
  43         if ((e = strstr(tokens[1], "Out of range"))) {
  44                 is_oor = TRUE;
  45                 fvalue = -1;
  46                 while (*e && *e != '.')
  47                         e++;
  48         } else {
  49                 is_oor = FALSE;
  50                 /* Delimit the float, since sr_atof_ascii() wants only
  51                  * a valid float here. */
  52                 e = tokens[1];
  53                 while (*e && *e != ' ')
  54                         e++;
  55                 *e++ = '\0';
  56                 if (sr_atof_ascii(tokens[1], &fvalue) != SR_OK || fvalue == 0.0) {
  57                         /* Happens all the time, when switching modes. */
  58                         sr_dbg("Invalid float.");
  59                         return NULL;
  60                 }
  61         }
  62         while (*e && *e == ' ')
  63                 e++;
  64
  65         analog = g_malloc0(sizeof(struct sr_datafeed_analog));
  66         /* TODO: Use proper 'digits' value for this device (and its modes). */
  67         sr_analog_init(analog, &encoding, &meaning, &spec, 2);
  68         analog->data = g_malloc(sizeof(float));
  69         analog->meaning->channels = sdi->channels;
  70         analog->num_samples = 1;
  71         if (is_oor)
  72                 *((float *)analog->data) = NAN;
  73         else
  74                 *((float *)analog->data) = fvalue;
  75         analog->meaning->mq = 0;
  76
  77         if ((u = strstr(e, "V DC")) || (u = strstr(e, "V AC"))) {
  78                 analog->meaning->mq = SR_MQ_VOLTAGE;
  79                 analog->meaning->unit = SR_UNIT_VOLT;
  80                 if (!is_oor && e[0] == 'm')
  81                         *((float *)analog->data) /= 1000;
  82                 /* This catches "V AC", "V DC" and "V AC+DC". */
  83                 if (strstr(u, "AC"))
  84                         analog->meaning->mqflags |= SR_MQFLAG_AC | SR_MQFLAG_RMS;
  85                 if (strstr(u, "DC"))
  86                         analog->meaning->mqflags |= SR_MQFLAG_DC;
  87         } else if ((u = strstr(e, "dBV")) || (u = strstr(e, "dBm"))) {
  88                 analog->meaning->mq = SR_MQ_VOLTAGE;
  89                 if (u[2] == 'm')
  90                         analog->meaning->unit = SR_UNIT_DECIBEL_MW;
  91                 else
  92                         analog->meaning->unit = SR_UNIT_DECIBEL_VOLT;
  93                 analog->meaning->mqflags |= SR_MQFLAG_AC | SR_MQFLAG_RMS;
  94         } else if ((u = strstr(e, "Ohms"))) {
  95                 analog->meaning->mq = SR_MQ_RESISTANCE;
  96                 analog->meaning->unit = SR_UNIT_OHM;
  97                 if (is_oor)
  98                         *((float *)analog->data) = INFINITY;
  99                 else if (e[0] == 'k')
 100                         *((float *)analog->data) *= 1000;
 101                 else if (e[0] == 'M')
 102                         *((float *)analog->data) *= 1000000;
 103         } else if (!strcmp(e, "nS")) {
 104                 analog->meaning->mq = SR_MQ_CONDUCTANCE;
 105                 analog->meaning->unit = SR_UNIT_SIEMENS;
 106                 *((float *)analog->data) /= 1e+9;
 107         } else if ((u = strstr(e, "Farads"))) {
 108                 analog->meaning->mq = SR_MQ_CAPACITANCE;
 109                 analog->meaning->unit = SR_UNIT_FARAD;
 110                 if (!is_oor) {
 111                         if (e[0] == 'm')
 112                                 *((float *)analog->data) /= 1e+3;
 113                         else if (e[0] == 'u')
 114                                 *((float *)analog->data) /= 1e+6;
 115                         else if (e[0] == 'n')
 116                                 *((float *)analog->data) /= 1e+9;
 117                 }
 118         } else if ((u = strstr(e, "Deg C")) || (u = strstr(e, "Deg F"))) {
 119                 analog->meaning->mq = SR_MQ_TEMPERATURE;
 120                 if (u[4] == 'C')
 121                         analog->meaning->unit = SR_UNIT_CELSIUS;
 122                 else
 123                         analog->meaning->unit = SR_UNIT_FAHRENHEIT;
 124         } else if ((u = strstr(e, "A AC")) || (u = strstr(e, "A DC"))) {
 125                 analog->meaning->mq = SR_MQ_CURRENT;
 126                 analog->meaning->unit = SR_UNIT_AMPERE;
 127                 /* This catches "A AC", "A DC" and "A AC+DC". */
 128                 if (strstr(u, "AC"))
 129                         analog->meaning->mqflags |= SR_MQFLAG_AC | SR_MQFLAG_RMS;
 130                 if (strstr(u, "DC"))
 131                         analog->meaning->mqflags |= SR_MQFLAG_DC;
 132                 if (!is_oor) {
 133                         if (e[0] == 'm')
 134                                 *((float *)analog->data) /= 1e+3;
 135                         else if (e[0] == 'u')
 136                                 *((float *)analog->data) /= 1e+6;
 137                 }
 138         } else if ((u = strstr(e, "Hz"))) {
 139                 analog->meaning->mq = SR_MQ_FREQUENCY;
 140                 analog->meaning->unit = SR_UNIT_HERTZ;
 141                 if (e[0] == 'k')
 142                         *((float *)analog->data) *= 1e+3;
 143         } else if (!strcmp(e, "%")) {
 144                 analog->meaning->mq = SR_MQ_DUTY_CYCLE;
 145                 analog->meaning->unit = SR_UNIT_PERCENTAGE;
 146         } else if ((u = strstr(e, "ms"))) {
 147                 analog->meaning->mq = SR_MQ_PULSE_WIDTH;
 148                 analog->meaning->unit = SR_UNIT_SECOND;
 149                 *((float *)analog->data) /= 1e+3;
 150         }
 151
 152         if (analog->meaning->mq == 0) {
 153                 /* Not a valid measurement. */
 154                 g_free(analog->data);
 155                 g_free(analog);
 156                 analog = NULL;
 157         }
 158
 159         return analog;
 160 }
 161
 162 static struct sr_datafeed_analog *handle_qm_28x(const struct sr_dev_inst *sdi,
 163                 char **tokens)
 164 {
 165         struct sr_datafeed_analog *analog;
 166         struct sr_analog_encoding encoding;
 167         struct sr_analog_meaning meaning;
 168         struct sr_analog_spec spec;
 169         float fvalue;
 170
 171         if (!tokens[1])
 172                 return NULL;
 173
 174         if (sr_atof_ascii(tokens[0], &fvalue) != SR_OK || fvalue == 0.0) {
 175                 sr_err("Invalid float '%s'.", tokens[0]);
 176                 return NULL;
 177         }
 178
 179         analog = g_malloc0(sizeof(struct sr_datafeed_analog));
 180         /* TODO: Use proper 'digits' value for this device (and its modes). */
 181         sr_analog_init(analog, &encoding, &meaning, &spec, 2);
 182         analog->data = g_malloc(sizeof(float));
 183         analog->meaning->channels = sdi->channels;
 184         analog->num_samples = 1;
 185         *((float *)analog->data) = fvalue;
 186         analog->meaning->mq = 0;
 187
 188         if (!strcmp(tokens[1], "VAC") || !strcmp(tokens[1], "VDC")) {
 189                 analog->meaning->mq = SR_MQ_VOLTAGE;
 190                 analog->meaning->unit = SR_UNIT_VOLT;
 191                 if (!strcmp(tokens[2], "NORMAL")) {
 192                         if (tokens[1][1] == 'A') {
 193                                 analog->meaning->mqflags |= SR_MQFLAG_AC;
 194                                 analog->meaning->mqflags |= SR_MQFLAG_RMS;
 195                         } else
 196                                 analog->meaning->mqflags |= SR_MQFLAG_DC;
 197                 } else if (!strcmp(tokens[2], "OL") || !strcmp(tokens[2], "OL_MINUS")) {
 198                         *((float *)analog->data) = NAN;
 199                 } else
 200                         analog->meaning->mq = 0;
 201         } else if (!strcmp(tokens[1], "dBV") || !strcmp(tokens[1], "dBm")) {
 202                 analog->meaning->mq = SR_MQ_VOLTAGE;
 203                 if (tokens[1][2] == 'm')
 204                         analog->meaning->unit = SR_UNIT_DECIBEL_MW;
 205                 else
 206                         analog->meaning->unit = SR_UNIT_DECIBEL_VOLT;
 207                 analog->meaning->mqflags |= SR_MQFLAG_AC | SR_MQFLAG_RMS;
 208         } else if (!strcmp(tokens[1], "CEL") || !strcmp(tokens[1], "FAR")) {
 209                 if (!strcmp(tokens[2], "NORMAL")) {
 210                         analog->meaning->mq = SR_MQ_TEMPERATURE;
 211                         if (tokens[1][0] == 'C')
 212                                 analog->meaning->unit = SR_UNIT_CELSIUS;
 213                         else
 214                                 analog->meaning->unit = SR_UNIT_FAHRENHEIT;
 215                 }
 216         } else if (!strcmp(tokens[1], "OHM")) {
 217                 if (!strcmp(tokens[3], "NONE")) {
 218                         analog->meaning->mq = SR_MQ_RESISTANCE;
 219                         analog->meaning->unit = SR_UNIT_OHM;
 220                         if (!strcmp(tokens[2], "OL") || !strcmp(tokens[2], "OL_MINUS")) {
 221                                 *((float *)analog->data) = INFINITY;
 222                         } else if (strcmp(tokens[2], "NORMAL"))
 223                                 analog->meaning->mq = 0;
 224                 } else if (!strcmp(tokens[3], "OPEN_CIRCUIT")) {
 225                         analog->meaning->mq = SR_MQ_CONTINUITY;
 226                         analog->meaning->unit = SR_UNIT_BOOLEAN;
 227                         *((float *)analog->data) = 0.0;
 228                 } else if (!strcmp(tokens[3], "SHORT_CIRCUIT")) {
 229                         analog->meaning->mq = SR_MQ_CONTINUITY;
 230                         analog->meaning->unit = SR_UNIT_BOOLEAN;
 231                         *((float *)analog->data) = 1.0;
 232                 }
 233         } else if (!strcmp(tokens[1], "F")
 234                         && !strcmp(tokens[2], "NORMAL")
 235                         && !strcmp(tokens[3], "NONE")) {
 236                 analog->meaning->mq = SR_MQ_CAPACITANCE;
 237                 analog->meaning->unit = SR_UNIT_FARAD;
 238         } else if (!strcmp(tokens[1], "AAC") || !strcmp(tokens[1], "ADC")) {
 239                 analog->meaning->mq = SR_MQ_CURRENT;
 240                 analog->meaning->unit = SR_UNIT_AMPERE;
 241                 if (!strcmp(tokens[2], "NORMAL")) {
 242                         if (tokens[1][1] == 'A') {
 243                                 analog->meaning->mqflags |= SR_MQFLAG_AC;
 244                                 analog->meaning->mqflags |= SR_MQFLAG_RMS;
 245                         } else
 246                                 analog->meaning->mqflags |= SR_MQFLAG_DC;
 247                 } else if (!strcmp(tokens[2], "OL") || !strcmp(tokens[2], "OL_MINUS")) {
 248                         *((float *)analog->data) = NAN;
 249                 } else
 250                         analog->meaning->mq = 0;
 251         } if (!strcmp(tokens[1], "Hz") && !strcmp(tokens[2], "NORMAL")) {
 252                 analog->meaning->mq = SR_MQ_FREQUENCY;
 253                 analog->meaning->unit = SR_UNIT_HERTZ;
 254         } else if (!strcmp(tokens[1], "PCT") && !strcmp(tokens[2], "NORMAL")) {
 255                 analog->meaning->mq = SR_MQ_DUTY_CYCLE;
 256                 analog->meaning->unit = SR_UNIT_PERCENTAGE;
 257         } else if (!strcmp(tokens[1], "S") && !strcmp(tokens[2], "NORMAL")) {
 258                 analog->meaning->mq = SR_MQ_PULSE_WIDTH;
 259                 analog->meaning->unit = SR_UNIT_SECOND;
 260         } else if (!strcmp(tokens[1], "SIE") && !strcmp(tokens[2], "NORMAL")) {
 261                 analog->meaning->mq = SR_MQ_CONDUCTANCE;
 262                 analog->meaning->unit = SR_UNIT_SIEMENS;
 263         }
 264
 265         if (analog->meaning->mq == 0) {
 266                 /* Not a valid measurement. */
 267                 g_free(analog->data);
 268                 g_free(analog);
 269                 analog = NULL;
 270         }
 271
 272         return analog;
 273 }
 274
 275 static void handle_qm_19x_meta(const struct sr_dev_inst *sdi, char **tokens)
 276 {
 277         struct dev_context *devc;
 278         int meas_type, meas_unit, meas_char, i;
 279
 280         /* Make sure we have 7 valid tokens. */
 281         for (i = 0; tokens[i] && i < 7; i++);
 282         if (i != 7)
 283                 return;
 284
 285         if (strcmp(tokens[1], "1"))
 286                 /* Invalid measurement. */
 287                 return;
 288
 289         if (strcmp(tokens[2], "3"))
 290                 /* Only interested in input from the meter mode source. */
 291                 return;
 292
 293         devc = sdi->priv;
 294
 295         /* Measurement type 11 == absolute, 19 = relative */
 296         meas_type = strtol(tokens[0], NULL, 10);
 297         if (meas_type != 11 && meas_type != 19)
 298                 /* Device is in some mode we don't support. */
 299                 return;
 300
 301         /* We might get metadata for absolute and relative mode (if the device
 302          * is in relative mode). In that case, relative takes precedence. */
 303         if (meas_type == 11 && devc->meas_type == 19)
 304                 return;
 305
 306         meas_unit = strtol(tokens[3], NULL, 10);
 307         if (meas_unit == 0)
 308                 /* Device is turned off. Really. */
 309                 return;
 310         meas_char = strtol(tokens[4], NULL, 10);
 311
 312         devc->mq = 0;
 313         devc->unit = 0;
 314         devc->mqflags = 0;
 315
 316         switch (meas_unit) {
 317         case 1:
 318                 devc->mq = SR_MQ_VOLTAGE;
 319                 devc->unit = SR_UNIT_VOLT;
 320                 if (meas_char == 1)
 321                         devc->mqflags |= SR_MQFLAG_DC;
 322                 else if (meas_char == 2)
 323                         devc->mqflags |= SR_MQFLAG_AC;
 324                 else if (meas_char == 3)
 325                         devc->mqflags |= SR_MQFLAG_DC | SR_MQFLAG_AC;
 326                 else if (meas_char == 15)
 327                         devc->mqflags |= SR_MQFLAG_DIODE;
 328                 break;
 329         case 2:
 330                 devc->mq = SR_MQ_CURRENT;
 331                 devc->unit = SR_UNIT_AMPERE;
 332                 if (meas_char == 1)
 333                         devc->mqflags |= SR_MQFLAG_DC;
 334                 else if (meas_char == 2)
 335                         devc->mqflags |= SR_MQFLAG_AC;
 336                 else if (meas_char == 3)
 337                         devc->mqflags |= SR_MQFLAG_DC | SR_MQFLAG_AC;
 338                 break;
 339         case 3:
 340                 if (meas_char == 1) {
 341                         devc->mq = SR_MQ_RESISTANCE;
 342                         devc->unit = SR_UNIT_OHM;
 343                 } else if (meas_char == 16) {
 344                         devc->mq = SR_MQ_CONTINUITY;
 345                         devc->unit = SR_UNIT_BOOLEAN;
 346                 }
 347                 break;
 348         case 12:
 349                 devc->mq = SR_MQ_TEMPERATURE;
 350                 devc->unit = SR_UNIT_CELSIUS;
 351                 break;
 352         case 13:
 353                 devc->mq = SR_MQ_TEMPERATURE;
 354                 devc->unit = SR_UNIT_FAHRENHEIT;
 355                 break;
 356         default:
 357                 sr_dbg("unknown unit: %d", meas_unit);
 358         }
 359         if (devc->mq == 0 && devc->unit == 0)
 360                 return;
 361
 362         /* If we got here, we know how to interpret the measurement. */
 363         devc->meas_type = meas_type;
 364         if (meas_type == 11)
 365                 /* Absolute meter reading. */
 366                 devc->is_relative = FALSE;
 367         else if (!strcmp(tokens[0], "19"))
 368                 /* Relative meter reading. */
 369                 devc->is_relative = TRUE;
 370
 371 }
 372
 373 static void handle_qm_19x_data(const struct sr_dev_inst *sdi, char **tokens)
 374 {
 375         struct dev_context *devc;
 376         struct sr_datafeed_packet packet;
 377         struct sr_datafeed_analog analog;
 378         struct sr_analog_encoding encoding;
 379         struct sr_analog_meaning meaning;
 380         struct sr_analog_spec spec;
 381         float fvalue;
 382
 383         if (!strcmp(tokens[0], "9.9E+37")) {
 384                 /* An invalid measurement shows up on the display as "OL", but
 385                  * comes through like this. Since comparing 38-digit floats
 386                  * is rather problematic, we'll cut through this here. */
 387                 fvalue = NAN;
 388         } else {
 389                 if (sr_atof_ascii(tokens[0], &fvalue) != SR_OK || fvalue == 0.0) {
 390                         sr_err("Invalid float '%s'.", tokens[0]);
 391                         return;
 392                 }
 393         }
 394
 395         devc = sdi->priv;
 396         if (devc->mq == 0 || devc->unit == 0)
 397                 /* Don't have valid metadata yet. */
 398                 return;
 399
 400         if (devc->mq == SR_MQ_RESISTANCE && isnan(fvalue))
 401                 fvalue = INFINITY;
 402         else if (devc->mq == SR_MQ_CONTINUITY) {
 403                 if (isnan(fvalue))
 404                         fvalue = 0.0;
 405                 else
 406                         fvalue = 1.0;
 407         }
 408
 409         /* TODO: Use proper 'digits' value for this device (and its modes). */
 410         sr_analog_init(&analog, &encoding, &meaning, &spec, 2);
 411         analog.meaning->channels = sdi->channels;
 412         analog.num_samples = 1;
 413         analog.data = &fvalue;
 414         analog.meaning->mq = devc->mq;
 415         analog.meaning->unit = devc->unit;
 416         analog.meaning->mqflags = 0;
 417         packet.type = SR_DF_ANALOG;
 418         packet.payload = &analog;
 419         sr_session_send(sdi, &packet);
 420
 421         sr_sw_limits_update_samples_read(&devc->limits, 1);
 422 }
 423
 424 static void handle_line(const struct sr_dev_inst *sdi)
 425 {
 426         struct dev_context *devc;
 427         struct sr_serial_dev_inst *serial;
 428         struct sr_datafeed_packet packet;
 429         struct sr_datafeed_analog *analog;
 430         int num_tokens, n, i;
 431         char cmd[16], **tokens;
 432
 433         devc = sdi->priv;
 434         serial = sdi->conn;
 435         sr_spew("Received line '%s' (%d).", devc->buf, devc->buflen);
 436
 437         if (devc->buflen == 1) {
 438                 if (devc->buf[0] != '0') {
 439                         /* Not just a CMD_ACK from the query command. */
 440                         sr_dbg("Got CMD_ACK '%c'.", devc->buf[0]);
 441                         devc->expect_response = FALSE;
 442                 }
 443                 devc->buflen = 0;
 444                 return;
 445         }
 446
 447         analog = NULL;
 448         tokens = g_strsplit(devc->buf, ",", 0);
 449         if (tokens[0]) {
 450                 if (devc->profile->model == FLUKE_187 || devc->profile->model == FLUKE_189) {
 451                         devc->expect_response = FALSE;
 452                         analog = handle_qm_18x(sdi, tokens);
 453                 } else if (devc->profile->model == FLUKE_287 || devc->profile->model == FLUKE_289) {
 454                         devc->expect_response = FALSE;
 455                         analog = handle_qm_28x(sdi, tokens);
 456                 } else if (devc->profile->model == FLUKE_190) {
 457                         devc->expect_response = FALSE;
 458                         for (num_tokens = 0; tokens[num_tokens]; num_tokens++);
 459                         if (num_tokens >= 7) {
 460                                 /* Response to QM: this is a comma-separated list of
 461                                  * fields with metadata about the measurement. This
 462                                  * format can return multiple sets of metadata,
 463                                  * split into sets of 7 tokens each. */
 464                                 devc->meas_type = 0;
 465                                 for (i = 0; i < num_tokens; i += 7)
 466                                         handle_qm_19x_meta(sdi, tokens + i);
 467                                 if (devc->meas_type) {
 468                                         /* Slip the request in now, before the main
 469                                          * timer loop asks for metadata again. */
 470                                         n = sprintf(cmd, "QM %d\r", devc->meas_type);
 471                                         if (serial_write_blocking(serial, cmd, n, SERIAL_WRITE_TIMEOUT_MS) < 0)
 472                                                 sr_err("Unable to send QM (measurement).");
 473                                 }
 474                         } else {
 475                                 /* Response to QM <n> measurement request. */
 476                                 handle_qm_19x_data(sdi, tokens);
 477                         }
 478                 }
 479         }
 480         g_strfreev(tokens);
 481         devc->buflen = 0;
 482
 483         if (analog) {
 484                 /* Got a measurement. */
 485                 packet.type = SR_DF_ANALOG;
 486                 packet.payload = analog;
 487                 sr_session_send(sdi, &packet);
 488                 sr_sw_limits_update_samples_read(&devc->limits, 1);
 489                 g_free(analog->data);
 490                 g_free(analog);
 491         }
 492
 493 }
 494
 495 SR_PRIV int fluke_receive_data(int fd, int revents, void *cb_data)
 496 {
 497         struct sr_dev_inst *sdi;
 498         struct dev_context *devc;
 499         struct sr_serial_dev_inst *serial;
 500         int len;
 501         int64_t now, elapsed;
 502
 503         (void)fd;
 504
 505         if (!(sdi = cb_data))
 506                 return TRUE;
 507
 508         if (!(devc = sdi->priv))
 509                 return TRUE;
 510
 511         serial = sdi->conn;
 512         if (revents == G_IO_IN) {
 513                 /* Serial data arrived. */
 514                 while (FLUKEDMM_BUFSIZE - devc->buflen - 1 > 0) {
 515                         len = serial_read_nonblocking(serial, devc->buf + devc->buflen, 1);
 516                         if (len < 1)
 517                                 break;
 518                         devc->buflen++;
 519                         *(devc->buf + devc->buflen) = '\0';
 520                         if (*(devc->buf + devc->buflen - 1) == '\r') {
 521                                 *(devc->buf + --devc->buflen) = '\0';
 522                                 handle_line(sdi);
 523                                 break;
 524                         }
 525                 }
 526         }
 527
 528         if (sr_sw_limits_check(&devc->limits)) {
 529                 sr_dev_acquisition_stop(sdi);
 530                 return TRUE;
 531         }
 532
 533         now = g_get_monotonic_time() / 1000;
 534         elapsed = now - devc->cmd_sent_at;
 535         /* Send query command at poll_period interval, or after 1 second
 536          * has elapsed. This will make it easier to recover from any
 537          * out-of-sync or temporary disconnect issues. */
 538         if ((devc->expect_response == FALSE && elapsed > devc->profile->poll_period)
 539                         || elapsed > devc->profile->timeout) {
 540                 if (serial_write_blocking(serial, "QM\r", 3, SERIAL_WRITE_TIMEOUT_MS) < 0)
 541                         sr_err("Unable to send QM.");
 542                 devc->cmd_sent_at = now;
 543                 devc->expect_response = TRUE;
 544         }
 545
 546         return TRUE;
 547 }