87 lines
3.0 KiB
ReStructuredText
87 lines
3.0 KiB
ReStructuredText
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Kernel driver w1_ds2438
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=======================
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Supported chips:
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* Maxim DS2438 Smart Battery Monitor
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supported family codes:
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================ ====
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W1_FAMILY_DS2438 0x26
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================ ====
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Author: Mariusz Bialonczyk <manio@skyboo.net>
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Description
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-----------
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The DS2438 chip provides several functions that are desirable to carry in
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a battery pack. It also has a 40 bytes of nonvolatile EEPROM.
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Because the ability of temperature, current and voltage measurement, the chip
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is also often used in weather stations and applications such as: rain gauge,
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wind speed/direction measuring, humidity sensing, etc.
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Current support is provided through the following sysfs files (all files
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except "iad" and "offset" are readonly):
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"iad"
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-----
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This file controls the 'Current A/D Control Bit' (IAD) in the
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Status/Configuration Register.
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Writing a zero value will clear the IAD bit and disables the current
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measurements.
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Writing value "1" is setting the IAD bit (enables the measurements).
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The IAD bit is enabled by default in the DS2438.
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When writing to sysfs file bits 2-7 are ignored, so it's safe to write ASCII.
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An I/O error is returned when there is a problem setting the new value.
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"page0"
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-------
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This file provides full 8 bytes of the chip Page 0 (00h).
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This page contains the most frequently accessed information of the DS2438.
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Internally when this file is read, the additional CRC byte is also obtained
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from the slave device. If it is correct, the 8 bytes page data are passed
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to userspace, otherwise an I/O error is returned.
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"page1"
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-------
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This file provides full 8 bytes of the chip Page 1 (01h).
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This page contains the ICA, elapsed time meter and current offset data of the DS2438.
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Internally when this file is read, the additional CRC byte is also obtained
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from the slave device. If it is correct, the 8 bytes page data are passed
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to userspace, otherwise an I/O error is returned.
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"offset"
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--------
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This file controls the 2-byte Offset Register of the chip.
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Writing a 2-byte value will change the Offset Register, which changes the
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current measurement done by the chip. Changing this register to the two's complement
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of the current register while forcing zero current through the load will calibrate
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the chip, canceling offset errors in the current ADC.
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"temperature"
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-------------
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Opening and reading this file initiates the CONVERT_T (temperature conversion)
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command of the chip, afterwards the temperature is read from the device
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registers and provided as an ASCII decimal value.
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Important: The returned value has to be divided by 256 to get a real
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temperature in degrees Celsius.
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"vad", "vdd"
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------------
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Opening and reading this file initiates the CONVERT_V (voltage conversion)
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command of the chip.
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Depending on a sysfs filename a different input for the A/D will be selected:
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vad:
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general purpose A/D input (VAD)
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vdd:
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battery input (VDD)
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After the voltage conversion the value is returned as decimal ASCII.
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Note: To get a volts the value has to be divided by 100.
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