cp2112_BME680

What is CP2112?

• USB<->I2C conversion chip (Silicon Laboratories Single-Chip HID USB to SMBus Master Bridg) for Linux and Windows USB You can use 8 GPIOs and I2C from, here we are using the module board of Sunhayato’s MM-CP2122A.

• MM-CP2122A Selling phraseI2C connection sensor and GPIO (8 pin) can be controlled directly from a PC application without programming the microcomputer. is a difficult task, and programming requires an understanding of the HIDAPI and CP2112 interface specifications below.

  • Hidapi Reference
  • CP2112 Reference AN495: CP2112 Interface Specification
  • I2C connection device verified this time BME680 hardware data

• When I connect to the USB of my lubuntu lts 18.04 Linux machine, the driver is loaded as shown below and the HID device is recognized.

  # lsmod |grep cp2112
  hid_cp2112             24576  0
  hid                   102400  3 hid_cp2112,hid_generic,usbhid
  # ll /dev/hidraw-cp2112
  lrwxrwxrwx 1 root root 7  4月  6 16:54 /dev/hidraw-cp2112 -> hidraw0

• From here, we verified the operation of GPIO and I2C connection temperature/humidity sensor AM2320 and environmental gas sensor BME680 based on the above materials and collected information pepocp2112ctl.cThe explanation is based on the program.

  

• Install the package for development libhidapi

  # apt install libhidapi-dev
  libhidapi-dev libhidapi-hidraw0 libhidapi-libusb0

• Get and compile the following filesFork from BoschSensortec/BME680_driver

  bme680.c  bme680.h  bme680_defs.h  pepocp2112ctl.c
  # gcc -Wall -o pepocp2112ctl pepocp2112ctl.c bme680.c -lhidapi-hidraw
  # ll
  total 144
  drwxr-xr-x 2 root     root       140  4月  6 17:39 ./
  drwxr-xr-x 3 www-data www-data   840  4月  6 17:39 ../
  -rwxr-xr-x 1 root     root     44364  4月 13  2019 bme680.c*
  -rwxr-xr-x 1 root     root      8353  4月 13  2019 bme680.h*
  -rwxr-xr-x 1 root     root     17134  4月 13  2019 bme680_defs.h*
  -rwxr-xr-x 1 root     root     34644  4月  6 17:39 pepocp2112ctl*
  -rw-r--r-- 1 root     root     30626  3月 28 16:26 pepocp2112ctl.c

• Programming example, SMBus Devices operation only Extract from source and explain only important parts, check the source for others. (Experience shows that GPIO needs to be operated in multiple processes, so there is a considerable amount using semaphore.)

  • CP2112’s I2C connection device BME680 sets the I2C address, required commands, data, and byte counter in the buffer, sends it with hid_send_feature_report, and waits for a response to the command if necessary.
  • The BME680 write sets the command(CP2112_DATA_WRITE), register address, data, and number of bytes and writes it to the device.

    int8_t user_i2c_write(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
    {
      .
      reg[0] = CP2112_DATA_WRITE;
      reg[1] = BME680_I2C_ADDR_PRIMARY<<1;
      reg[2] = len+1;
      reg[3] = reg_addr;
      for (int8_t i=4; i<len+4; i++)
        reg[i] = reg_data[i-4];
      rslt = hid_send_feature_report(hd, reg, len+4);

    • Dump of buffer etc. during debugging

      user_i2c_write() dev_id: ec reg_addr: e0 len: 1
      user_i2c_write()1 rslt: 5 len: 1
      reg dump start
      0:14 1:ec 2:02 3:e0 4:b6
      reg dump end

  • The BME680 read first sends the register address with a write command.
    Next, send the I2C address read request command(CP2112_DATA_READ_REQ),Wait for Polling, status confirmation(CP2112_DATA_READ_RESPONS),until the data is ready(CP2112_DATA_READ_FORCE_SEND),and then read the data from the device.

    int8_t user_i2c_read(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
    {
      .
      reg[0] = CP2112_DATA_WRITE;
      reg[1] = BME680_I2C_ADDR_PRIMARY<<1;
      reg[2] = 1;
      reg[3] = reg_addr;
      rslt = hid_send_feature_report(hd, reg, 4);
      .
      user_delay_ms(HID_WAIT);
      reg[0] = CP2112_DATA_READ_REQ;
      reg[1] = BME680_I2C_ADDR_PRIMARY<<1;
      reg[2] = 0x00; // reads length_high
      reg[3] = len; // reads length_low
      rslt = hid_send_feature_report(hd, reg, 4);
      .
      user_delay_ms(HID_WAIT);
      while (retry_cnt < 3)
      {
    /*  SMBus Polling */
        reg[0] = CP2112_DATA_READ_FORCE_SEND;
        reg[1] = 0x00; // reads length_high
        reg[2] = len; // reads length_low
        rslt = hid_send_feature_report(hd, reg, 3);
        .
        user_delay_ms(HID_WAIT);
        rslt = hid_read_timeout(hd, buf_in, len+3, timeout);
        .
    /*
        buf_in[0]:hid_report ID->0x13:CP2112_DATA_READ_RESPONS
        buf_in[1]:hid_status 0x00->Idle ,x01->Busy ,x02->Complete
        ,buf_in[2]:hid_read_length
        buf_in[3]-:Following_BME680_Read_Data
    */
        if (buf_in[0] == CP2112_DATA_READ_RESPONS)
        {
          if (buf_in[1] == 0x00 || buf_in[1] == 0x02 || buf_in[1] == 0x03)
            .
            break;
          retry_cnt++; // Busy or Idle or Other
          user_delay_ms(HID_WAIT);
          continue;
        }
        if (buf_in[0] == CP2112_TRANSFER_STATUS_RESP)
        {
          .
          user_delay_ms(HID_WAIT);
          retry_cnt++;
          continue;
        }
      }
      .
      if(buf_in[2] > 0 && rslt > 3 && buf_in[2] < rslt)
      {
        int8_t j = buf_in[2];
        for (int8_t i=0; i < j; i++)
        {
          reg_data[i] = buf_in[i+3];
        }
        return 0;
      }

    • Dump of buffer etc. during debugging

      user_i2c_read dev_id: ec reg_addr: d0 reg_data: 04 len: 1
      user_i2c_read()hid_read_timeout rslt:4 retry_cnt:0
      buf_in dump start
      0:13 1:02 2:01 3:61
      buf_in dump end
      
      user_i2c_read dev_id: ec reg_addr: 89 reg_data: 04 len: 25
      user_i2c_read()hid_read_timeout rslt:28 retry_cnt:0
      buf_in dump start
      0:13 1:02 2:19 3:40 4:a3 5:66 6:03 7:2f 8:80 9:8e 10:c9 11:d6 12:58 13:ff 14:de 15:19 16:cf 17:ff 18:2f 19:1e 20:00 21:00 22:1a 23:f3 24:e7 25:f6 26:1e 27:02
      buf_in dump end

• Please check the source code below
  https://github.com/kujiranodanna/BME680_driver