dallas_temp.cpp

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#include "dallas_temp.h"
#include "esphome/core/helpers.h"
#include "esphome/core/log.h"
 
namespace esphome::dallas_temp {
 
ESPHOME_LOG_TAG(TAG, "dallas.temp.sensor");
 
static constexpr uint32_t CONVERSION_TIMEOUT_ID = 0;
 
static const uint8_t DALLAS_MODEL_DS18S20 = 0x10;
static const uint8_t DALLAS_MODEL_DS18B20 = 0x28;
static const uint8_t DALLAS_COMMAND_START_CONVERSION = 0x44;
static const uint8_t DALLAS_COMMAND_READ_SCRATCH_PAD = 0xBE;
static const uint8_t DALLAS_COMMAND_WRITE_SCRATCH_PAD = 0x4E;
static const uint8_t DALLAS_COMMAND_COPY_SCRATCH_PAD = 0x48;
 
uint16_t DallasTemperatureSensor::millis_to_wait_for_conversion_() const {
  switch (this->resolution_) {
    case 9:
      return 94;
    case 10:
      return 188;
    case 11:
      return 375;
    default:
      return 750;
  }
}
 
void DallasTemperatureSensor::dump_config() {
  ESP_LOGCONFIG(TAG, "Dallas Temperature Sensor:");
  if (this->address_ == 0) {
    ESP_LOGW(TAG, "  Unable to select an address");
    return;
  }
  LOG_ONE_WIRE_DEVICE(this);
  ESP_LOGCONFIG(TAG, "  Resolution: %u bits", this->resolution_);
  LOG_UPDATE_INTERVAL(this);
}
 
void DallasTemperatureSensor::update() {
  if (this->address_ == 0)
    return;
 
  this->status_clear_warning();
 
  this->send_command_(DALLAS_COMMAND_START_CONVERSION);
 
  this->set_timeout(CONVERSION_TIMEOUT_ID, this->millis_to_wait_for_conversion_(), [this] {
    if (!this->read_scratch_pad_() || !this->check_scratch_pad_()) {
      this->publish_state(NAN);
      return;
    }
 
    float tempc = this->get_temp_c_();
    ESP_LOGD(TAG, "'%s': Got Temperature=%f°C", LOG_STR_ARG(this->get_log_name()), tempc);
    this->publish_state(tempc);
  });
}
 
bool DallasTemperatureSensor::read_scratch_pad_() {
  bool success = this->send_command_(DALLAS_COMMAND_READ_SCRATCH_PAD);
  if (success) {
    for (uint8_t &i : this->scratch_pad_) {
      i = this->bus_->read8();
    }
  } else {
    ESP_LOGW(TAG, "'%s' - reading scratch pad failed bus reset", LOG_STR_ARG(this->get_log_name()));
    this->status_set_warning(LOG_STR("bus reset failed"));
  }
  return success;
}
 
void DallasTemperatureSensor::setup() {
  if (!this->check_address_or_index_())
    return;
  if (!this->read_scratch_pad_())
    return;
  if (!this->check_scratch_pad_())
    return;
 
  if ((this->address_ & 0xff) == DALLAS_MODEL_DS18S20) {
    // DS18S20 doesn't support resolution.
    ESP_LOGW(TAG, "DS18S20 doesn't support setting resolution");
    return;
  }
 
  uint8_t res;
  switch (this->resolution_) {
    case 12:
      res = 0x7F;
      break;
    case 11:
      res = 0x5F;
      break;
    case 10:
      res = 0x3F;
      break;
    case 9:
    default:
      res = 0x1F;
      break;
  }
 
  if (this->scratch_pad_[4] == res)
    return;
  this->scratch_pad_[4] = res;
 
  if (this->send_command_(DALLAS_COMMAND_WRITE_SCRATCH_PAD)) {
    this->bus_->write8(this->scratch_pad_[2]);  // high alarm temp
    this->bus_->write8(this->scratch_pad_[3]);  // low alarm temp
    this->bus_->write8(this->scratch_pad_[4]);  // resolution
  }
 
  // write value to EEPROM
  this->send_command_(DALLAS_COMMAND_COPY_SCRATCH_PAD);
}
 
bool DallasTemperatureSensor::check_scratch_pad_() {
  bool chksum_validity = (crc8(this->scratch_pad_, 8) == this->scratch_pad_[8]);
 
#ifdef ESPHOME_LOG_LEVEL_VERY_VERBOSE
  ESP_LOGVV(TAG, "Scratch pad: %02X.%02X.%02X.%02X.%02X.%02X.%02X.%02X.%02X (%02X)", this->scratch_pad_[0],
            this->scratch_pad_[1], this->scratch_pad_[2], this->scratch_pad_[3], this->scratch_pad_[4],
            this->scratch_pad_[5], this->scratch_pad_[6], this->scratch_pad_[7], this->scratch_pad_[8],
            crc8(this->scratch_pad_, 8));
#endif
  if (!chksum_validity) {
    this->status_set_warning(LOG_STR("scratch pad checksum invalid"));
    ESP_LOGD(TAG, "Scratch pad: %02X.%02X.%02X.%02X.%02X.%02X.%02X.%02X.%02X (%02X)", this->scratch_pad_[0],
             this->scratch_pad_[1], this->scratch_pad_[2], this->scratch_pad_[3], this->scratch_pad_[4],
             this->scratch_pad_[5], this->scratch_pad_[6], this->scratch_pad_[7], this->scratch_pad_[8],
             crc8(this->scratch_pad_, 8));
  }
  return chksum_validity;
}
 
float DallasTemperatureSensor::get_temp_c_() {
  int16_t temp = encode_value_le<int16_t>(this->scratch_pad_);
  if ((this->address_ & 0xff) == DALLAS_MODEL_DS18S20) {
    if (this->scratch_pad_[7] == 0) {
      return NAN;
    }
    return (temp >> 1) + (this->scratch_pad_[7] - this->scratch_pad_[6]) / float(this->scratch_pad_[7]) - 0.25f;
  }
  switch (this->resolution_) {
    case 9:
      temp &= 0xfff8;
      break;
    case 10:
      temp &= 0xfffc;
      break;
    case 11:
      temp &= 0xfffe;
      break;
    case 12:
    default:
      break;
  }
  // undocumented test for powerup measurement of 85
  // https://github.com/cpetrich/counterfeit_DS18B20#solution-to-the-85-c-problem
  if ((this->address_ & 0xff) == DALLAS_MODEL_DS18B20) {
    if ((temp == 85 * 16) && (this->scratch_pad_[6] == 0xc)) {
      ESP_LOGD(TAG, "dropping reading caused by sensor reset");
      return NAN;
    }
  }
  return temp / 16.0f;
}
 
}  // namespace esphome::dallas_temp