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Diffstat (limited to 'Documentation/w1/slaves/w1_therm.rst')
| -rw-r--r-- | Documentation/w1/slaves/w1_therm.rst | 106 |
1 files changed, 72 insertions, 34 deletions
diff --git a/Documentation/w1/slaves/w1_therm.rst b/Documentation/w1/slaves/w1_therm.rst index cc4edae17751..6aec04dd0905 100644 --- a/Documentation/w1/slaves/w1_therm.rst +++ b/Documentation/w1/slaves/w1_therm.rst @@ -6,6 +6,8 @@ Supported chips: * Maxim ds18*20 based temperature sensors. * Maxim ds1825 based temperature sensors. + * GXCAS GX20MH01 temperature sensor. + * Maxim MAX31850 thermoelement interface. Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru> @@ -13,8 +15,8 @@ Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru> Description ----------- -w1_therm provides basic temperature conversion for ds18*20 devices, and the -ds28ea00 device. +w1_therm provides basic temperature conversion for ds18*20, ds28ea00, GX20MH01 +and MAX31850 devices. Supported family codes: @@ -26,59 +28,72 @@ W1_THERM_DS1825 0x3B W1_THERM_DS28EA00 0x42 ==================== ==== -Support is provided through the sysfs w1_slave file. Each open and -read sequence will initiate a temperature conversion then provide two +Support is provided through the sysfs entry ``w1_slave``. Each open and +read sequence will initiate a temperature conversion, then provide two lines of ASCII output. The first line contains the nine hex bytes read along with a calculated crc value and YES or NO if it matched. If the crc matched the returned values are retained. The second line displays the retained values along with a temperature in millidegrees Centigrade after t=. -Alternatively, temperature can be read using temperature sysfs, it -return only temperature in millidegrees Centigrade. +Alternatively, temperature can be read using ``temperature`` sysfs, it +returns only the temperature in millidegrees Centigrade. -A bulk read of all devices on the bus could be done writing 'trigger' -in the therm_bulk_read sysfs entry at w1_bus_master level. This will -sent the convert command on all devices on the bus, and if parasite -powered devices are detected on the bus (and strong pullup is enable +A bulk read of all devices on the bus could be done writing ``trigger`` +to ``therm_bulk_read`` entry at w1_bus_master level. This will +send the convert command to all devices on the bus, and if parasite +powered devices are detected on the bus (and strong pullup is enabled in the module), it will drive the line high during the longer conversion time required by parasited powered device on the line. Reading -therm_bulk_read will return 0 if no bulk conversion pending, +``therm_bulk_read`` will return 0 if no bulk conversion pending, -1 if at least one sensor still in conversion, 1 if conversion is complete but at least one sensor value has not been read yet. Result temperature is -then accessed by reading the temperature sysfs entry of each device, which +then accessed by reading the ``temperature`` entry of each device, which may return empty if conversion is still in progress. Note that if a bulk read is sent but one sensor is not read immediately, the next access to -temperature on this device will return the temperature measured at the +``temperature`` on this device will return the temperature measured at the time of issue of the bulk read command (not the current temperature). -Writing a value between 9 and 12 to the sysfs w1_slave file will change the -precision of the sensor for the next readings. This value is in (volatile) -SRAM, so it is reset when the sensor gets power-cycled. +A strong pullup will be applied during the conversion if required. -To store the current precision configuration into EEPROM, the value 0 -has to be written to the sysfs w1_slave file. Since the EEPROM has a limited -amount of writes (>50k), this command should be used wisely. +``conv_time`` is used to get current conversion time (read), and +adjust it (write). A temperature conversion time depends on the device type and +its current resolution. Default conversion time is set by the driver according +to the device datasheet. A conversion time for many original device clones +deviate from datasheet specs. There are three options: 1) manually set the +correct conversion time by writing a value in milliseconds to ``conv_time``; 2) +auto measure and set a conversion time by writing ``1`` to +``conv_time``; 3) use ``features`` to enable poll for conversion +completion. Options 2, 3 can't be used in parasite power mode. To get back to +the default conversion time write ``0`` to ``conv_time``. -Alternatively, resolution can be set or read (value from 9 to 12) using the -dedicated resolution sysfs entry on each device. This sysfs entry is not -present for devices not supporting this feature. Driver will adjust the -correct conversion time for each device regarding to its resolution setting. -In particular, strong pullup will be applied if required during the conversion -duration. +Writing a resolution value (in bits) to ``w1_slave`` will change the +precision of the sensor for the next readings. Allowed resolutions are defined by +the sensor. Resolution is reset when the sensor gets power-cycled. -The write-only sysfs entry eeprom is an alternative for EEPROM operations: - * 'save': will save device RAM to EEPROM - * 'restore': will restore EEPROM data in device RAM. +To store the current resolution in EEPROM, write ``0`` to ``w1_slave``. +Since the EEPROM has a limited amount of writes (>50k), this command should be +used wisely. -ext_power syfs entry allow tho check the power status of each device. - * '0': device parasite powered - * '1': device externally powered +Alternatively, resolution can be read or written using the dedicated +``resolution`` entry on each device, if supported by the sensor. -sysfs alarms allow read or write TH and TL (Temperature High an Low) alarms. +Some non-genuine DS18B20 chips are fixed in 12-bit mode only, so the actual +resolution is read back from the chip and verified. + +Note: Changing the resolution reverts the conversion time to default. + +The write-only sysfs entry ``eeprom_cmd`` is an alternative for EEPROM operations. +Write ``save`` to save device RAM to EEPROM. Write ``restore`` to restore EEPROM +data in device RAM. + +``ext_power`` entry allows checking the power state of each device. Reads +``0`` if the device is parasite powered, ``1`` if the device is externally powered. + +Sysfs ``alarms`` allow read or write TH and TL (Temperature High an Low) alarms. Values shall be space separated and in the device range (typical -55 degC to 125 degC). Values are integer as they are store in a 8bit register in -the device. Lowest value is automatically put to TL.Once set, alarms could +the device. Lowest value is automatically put to TL. Once set, alarms could be search at master level. The module parameter strong_pullup can be set to 0 to disable the @@ -102,5 +117,28 @@ The DS28EA00 provides an additional two pins for implementing a sequence detection algorithm. This feature allows you to determine the physical location of the chip in the 1-wire bus without needing pre-existing knowledge of the bus ordering. Support is provided through the sysfs -w1_seq file. The file will contain a single line with an integer value +``w1_seq``. The file will contain a single line with an integer value representing the device index in the bus starting at 0. + +``features`` sysfs entry controls optional driver settings per device. +Insufficient power in parasite mode, line noise and insufficient conversion +time may lead to conversion failure. Original DS18B20 and some clones allow for +detection of invalid conversion. Write bit mask ``1`` to ``features`` to enable +checking the conversion success. If byte 6 of scratchpad memory is 0xC after +conversion and temperature reads 85.00 (powerup value) or 127.94 (insufficient +power), the driver returns a conversion error. Bit mask ``2`` enables poll for +conversion completion (normal power only) by generating read cycles on the bus +after conversion starts. In parasite power mode this feature is not available. +Feature bit masks may be combined (OR). More details in +Documentation/ABI/testing/sysfs-driver-w1_therm + +GX20MH01 device shares family number 0x28 with DS18*20. The device is generally +compatible with DS18B20. Added are lowest 2\ :sup:`-5`, 2\ :sup:`-6` temperature +bits in Config register; R2 bit in Config register enabling 13 and 14 bit +resolutions. The device is powered up in 14-bit resolution mode. The conversion +times specified in the datasheet are too low and have to be increased. The +device supports driver features ``1`` and ``2``. + +MAX31850 device shares family number 0x3B with DS1825. The device is generally +compatible with DS1825. The higher 4 bits of Config register read all 1, +indicating 15, but the device is always operating in 14-bit resolution mode. |