projects / linux-2.6-block.git / blame
| Commit | Line | Data |
|---|---|---|
| f060c658 WM |
1 | Kernel driver htu21 |
| 2 | =================== | |
| 3 | ||
| 4 | Supported chips: | |
| 5 | * Measurement Specialties HTU21D | |
| 6 | Prefix: 'htu21' | |
| 7 | Addresses scanned: none | |
| 8 | Datasheet: Publicly available at the Measurement Specialties website | |
| 9 | http://www.meas-spec.com/downloads/HTU21D.pdf | |
| 10 | ||
| 11 | ||
| 12 | Author: | |
| 13 | William Markezana <william.markezana@meas-spec.com> | |
| 14 | ||
| 15 | Description | |
| 16 | ----------- | |
| 17 | ||
| 18 | The HTU21D is a humidity and temperature sensor in a DFN package of | |
| 19 | only 3 x 3 mm footprint and 0.9 mm height. | |
| 20 | ||
| 21 | The devices communicate with the I2C protocol. All sensors are set to the | |
| 22 | same I2C address 0x40, so an entry with I2C_BOARD_INFO("htu21", 0x40) can | |
| 23 | be used in the board setup code. | |
| 24 | ||
| 25 | This driver does not auto-detect devices. You will have to instantiate the | |
| 26 | devices explicitly. Please see Documentation/i2c/instantiating-devices | |
| 27 | for details. | |
| 28 | ||
| 29 | sysfs-Interface | |
| 30 | --------------- | |
| 31 | ||
| 32 | temp1_input - temperature input | |
| 33 | humidity1_input - humidity input | |
| 34 | ||
| 35 | Notes | |
| 36 | ----- | |
| 37 | ||
| 38 | The driver uses the default resolution settings of 12 bit for humidity and 14 | |
| 39 | bit for temperature, which results in typical measurement times of 11 ms for | |
| 40 | humidity and 44 ms for temperature. To keep self heating below 0.1 degree | |
| 41 | Celsius, the device should not be active for more than 10% of the time. For | |
| 42 | this reason, the driver performs no more than two measurements per second and | |
| 43 | reports cached information if polled more frequently. | |
| 44 | ||
| 45 | Different resolutions, the on-chip heater, using the CRC checksum and reading | |
| 46 | the serial number are not supported yet. |