Si70XX.h

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#ifndef Si70XX_H
#define Si70XX_H

#include "TWI.h"
#include <math.h>

#ifndef CHARBITS
#define CHARBITS 8
#endif

class Si70XX : protected TWI::Device {
public:
  Si70XX(TWI& twi) :
    TWI::Device(twi, 0x40)
  {}

  bool read_user_register(uint8_t &reg)
  {
    return (read(READ_RHT_USER_REG_1, reg));
  }

  bool read_electronic_serial_number(uint8_t snr[8])
  {
    uint8_t sna[8];
    uint8_t snb[6];
    uint16_t cmd;
    uint8_t crc;
    int count;
    size_t j;

    // Read SNA and check crc
    if (!acquire()) return (false);
    cmd = READ_ID_1;
    count = write(&cmd, sizeof(cmd));
    if (count != sizeof(cmd)) goto err;
    count = read(sna, sizeof(sna));
    if (count != sizeof(sna)) goto err;
    crc = 0;
    j = 0;
    for (size_t i = 0; i < sizeof(sna);) {
      crc = crc_update(crc, sna[i]);
      snr[j++] = sna[i++];
      if (sna[i++] != crc) goto err;
    }

    // Read SNB and check crc
    cmd = READ_ID_2;
    count = write(&cmd, sizeof(cmd));
    if (count != sizeof(cmd)) goto err;
    count = read(&snb, sizeof(snb));
    if (count != sizeof(snb)) goto err;
    crc = 0;
    for (size_t i = 0; i < sizeof(snb); ) {
      crc = crc_update(crc, snb[i]);
      snr[j++] = snb[i++];
      crc = crc_update(crc, snb[i]);
      snr[j++] = snb[i++];
      if (snb[i++] != crc) goto err;
    }
    return (release());

  err:
    release();
    return (false);
  }

  bool read_firmware_revision(uint8_t &rev)
  {
    uint16_t cmd = READ_REV;
    int count = 0;
    if (!acquire()) return (false);
    count = write(&cmd, sizeof(cmd));
    count = read(&rev, sizeof(rev));
    if (!release()) return (false);
    return (count == sizeof(rev));
  }

  bool measure_humidity()
  {
    return (issue(MEASURE_RH_NO_HOLD));
  }

  float read_humidity()
  {
    uint16_t value;
    if (!read(value)) (NAN);
    return (((125.00 * value) / 65536) - 6.00);
  }

  float read_humidity_temperature()
  {
    uint16_t value;
    if (!issue(READ_RH_TEMP)) return (NAN);
    if (!read(value, false)) return (NAN);
    return (((175.72 * value) / 65536) - 46.85);
  }

  bool measure_temperature()
  {
    return (issue(MEASURE_TEMP_NO_HOLD));
  }

  float read_temperature()
  {
    uint16_t value;
    if (!read(value)) return (NAN);
    return (((175.72 * value) / 65536) - 46.85);
  }

protected:
  enum Command {
    MEASURE_RH_HOLD = 0xE5,      
    MEASURE_RH_NO_HOLD = 0xF5,   
    MEASURE_TEMP_HOLD = 0xE3,    
    MEASURE_TEMP_NO_HOLD = 0xF3, 
    READ_RH_TEMP = 0xE0,         
    RESET = 0xFE,                
    WRITE_RHT_USER_REG_1 = 0xE6, 
    READ_RHT_USER_REG_1 = 0xE7,  
    READ_ID_1 = 0x0FFA,          
    READ_ID_2 = 0xC8FC,          
    READ_REV = 0xB884            
  } __attribute__((packed));

  bool issue(uint8_t cmd)
  {
    if (!acquire()) return (false);
    int count = write(&cmd, sizeof(cmd));
    if (!release()) return (false);
    return (count == sizeof(cmd));
  }

  bool read(uint16_t& value, bool check = true)
  {
    uint8_t buf[3];
    int size;
    int count = 0;

    size = check ? sizeof(buf) : sizeof(buf) - 1;
    for (int retry = 0; retry < 20; retry++) {
      if (acquire()) {
        count = read(buf, size);
        if (release() && count != -1) break;
      }
      delay(1);
    }
    if (count != size) return (false);
    value = ((buf[0] << 8) | buf[1]);
    if (!check) return (true);

    uint8_t crc;
    crc = crc_update(0, buf[0]);
    crc = crc_update(crc, buf[1]);
    return (crc == buf[2]);
  }

  bool read(uint8_t cmd, uint8_t& value)
  {
    uint8_t reg;
    int count = 0;
    if (!acquire()) return (false);
    write(&cmd, sizeof(cmd));
    count = read(&reg, sizeof(reg));
    if (!release() || count != sizeof(reg)) return (false);
    value = reg;
    return (true);
  }

  static uint8_t crc_update(uint8_t crc, uint8_t data)
  {
    crc ^= data;
    for (uint8_t i = CHARBITS; i != 0; i--) {
      uint8_t msb = (crc & 0x80);
      crc <<= 1;
      if (msb) crc ^= 0x31;
    }
    return (crc);
  }

  using Device::read;
};

#endif