projects / GitHub / MotorolaMobilityLLC / kernel-slsi.git / blame
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| 6d691550 MB |
1 | Kernel driver w1_ds2438 |
| 2 | ======================= | |
| 3 | ||
| 4 | Supported chips: | |
| 5 | * Maxim DS2438 Smart Battery Monitor | |
| 6 | ||
| 7 | supported family codes: | |
| 8 | W1_FAMILY_DS2438 0x26 | |
| 9 | ||
| 10 | Author: Mariusz Bialonczyk <manio@skyboo.net> | |
| 11 | ||
| 12 | Description | |
| 13 | ----------- | |
| 14 | ||
| 15 | The DS2438 chip provides several functions that are desirable to carry in | |
| 16 | a battery pack. It also has a 40 bytes of nonvolatile EEPROM. | |
| 17 | Because the ability of temperature, current and voltage measurement, the chip | |
| 18 | is also often used in weather stations and applications such as: rain gauge, | |
| 19 | wind speed/direction measuring, humidity sensing, etc. | |
| 20 | ||
| 21 | Current support is provided through the following sysfs files (all files | |
| 22 | except "iad" are readonly): | |
| 23 | ||
| 24 | "iad" | |
| 25 | ----- | |
| 26 | This file controls the 'Current A/D Control Bit' (IAD) in the | |
| 27 | Status/Configuration Register. | |
| 28 | Writing a zero value will clear the IAD bit and disables the current | |
| 29 | measurements. | |
| 30 | Writing value "1" is setting the IAD bit (enables the measurements). | |
| 31 | The IAD bit is enabled by default in the DS2438. | |
| 32 | ||
| 33 | When writing to sysfs file bits 2-7 are ignored, so it's safe to write ASCII. | |
| 34 | An I/O error is returned when there is a problem setting the new value. | |
| 35 | ||
| 36 | "page0" | |
| 37 | ------- | |
| 38 | This file provides full 8 bytes of the chip Page 0 (00h). | |
| 39 | This page contains the most frequently accessed information of the DS2438. | |
| 40 | Internally when this file is read, the additional CRC byte is also obtained | |
| 41 | from the slave device. If it is correct, the 8 bytes page data are passed | |
| 42 | to userspace, otherwise an I/O error is returned. | |
| 43 | ||
| 44 | "temperature" | |
| 45 | ------------- | |
| 46 | Opening and reading this file initiates the CONVERT_T (temperature conversion) | |
| 47 | command of the chip, afterwards the temperature is read from the device | |
| 48 | registers and provided as an ASCII decimal value. | |
| 49 | ||
| 50 | Important: The returned value has to be divided by 256 to get a real | |
| 51 | temperature in degrees Celsius. | |
| 52 | ||
| 53 | "vad", "vdd" | |
| 54 | ------------ | |
| 55 | Opening and reading this file initiates the CONVERT_V (voltage conversion) | |
| 56 | command of the chip. | |
| 57 | ||
| 58 | Depending on a sysfs filename a different input for the A/D will be selected: | |
| 59 | vad: general purpose A/D input (VAD) | |
| 60 | vdd: battery input (VDD) | |
| 61 | ||
| 62 | After the voltage conversion the value is returned as decimal ASCII. | |
| 63 | Note: The value is in mV, so to get a volts the value has to be divided by 10. |