1 ====================== 2 Kernel driver w1_therm 3 ====================== 4 5 Supported chips: 6 7 * Maxim ds18*20 based temperature sensors. 8 * Maxim ds1825 based temperature sensors. 9 * GXCAS GX20MH01 temperature sensor. 10 * Maxim MAX31850 thermoelement interface. 11 12 Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru> 13 14 15 Description 16 ----------- 17 18 w1_therm provides basic temperature conversion for ds18*20, ds28ea00, GX20MH01 19 and MAX31850 devices. 20 21 Supported family codes: 22 23 ==================== ==== 24 W1_THERM_DS18S20 0x10 25 W1_THERM_DS1822 0x22 26 W1_THERM_DS18B20 0x28 27 W1_THERM_DS1825 0x3B 28 W1_THERM_DS28EA00 0x42 29 ==================== ==== 30 31 Support is provided through the sysfs entry ``w1_slave``. Each open and 32 read sequence will initiate a temperature conversion, then provide two 33 lines of ASCII output. The first line contains the nine hex bytes 34 read along with a calculated crc value and YES or NO if it matched. 35 If the crc matched the returned values are retained. The second line 36 displays the retained values along with a temperature in millidegrees 37 Centigrade after t=. 38 39 Alternatively, temperature can be read using ``temperature`` sysfs, it 40 returns only the temperature in millidegrees Centigrade. 41 42 A bulk read of all devices on the bus could be done writing ``trigger`` 43 to ``therm_bulk_read`` entry at w1_bus_master level. This will 44 send the convert command to all devices on the bus, and if parasite 45 powered devices are detected on the bus (and strong pullup is enabled 46 in the module), it will drive the line high during the longer conversion 47 time required by parasited powered device on the line. Reading 48 ``therm_bulk_read`` will return 0 if no bulk conversion pending, 49 -1 if at least one sensor still in conversion, 1 if conversion is complete 50 but at least one sensor value has not been read yet. Result temperature is 51 then accessed by reading the ``temperature`` entry of each device, which 52 may return empty if conversion is still in progress. Note that if a bulk 53 read is sent but one sensor is not read immediately, the next access to 54 ``temperature`` on this device will return the temperature measured at the 55 time of issue of the bulk read command (not the current temperature). 56 57 A strong pullup will be applied during the conversion if required. 58 59 ``conv_time`` is used to get current conversion time (read), and 60 adjust it (write). A temperature conversion time depends on the device type and 61 its current resolution. Default conversion time is set by the driver according 62 to the device datasheet. A conversion time for many original device clones 63 deviate from datasheet specs. There are three options: 1) manually set the 64 correct conversion time by writing a value in milliseconds to ``conv_time``; 2) 65 auto measure and set a conversion time by writing ``1`` to 66 ``conv_time``; 3) use ``features`` to enable poll for conversion 67 completion. Options 2, 3 can't be used in parasite power mode. To get back to 68 the default conversion time write ``0`` to ``conv_time``. 69 70 Writing a resolution value (in bits) to ``w1_slave`` will change the 71 precision of the sensor for the next readings. Allowed resolutions are defined by 72 the sensor. Resolution is reset when the sensor gets power-cycled. 73 74 To store the current resolution in EEPROM, write ``0`` to ``w1_slave``. 75 Since the EEPROM has a limited amount of writes (>50k), this command should be 76 used wisely. 77 78 Alternatively, resolution can be read or written using the dedicated 79 ``resolution`` entry on each device, if supported by the sensor. 80 81 Some non-genuine DS18B20 chips are fixed in 12-bit mode only, so the actual 82 resolution is read back from the chip and verified. 83 84 Note: Changing the resolution reverts the conversion time to default. 85 86 The write-only sysfs entry ``eeprom_cmd`` is an alternative for EEPROM operations. 87 Write ``save`` to save device RAM to EEPROM. Write ``restore`` to restore EEPROM 88 data in device RAM. 89 90 ``ext_power`` entry allows checking the power state of each device. Reads 91 ``0`` if the device is parasite powered, ``1`` if the device is externally powered. 92 93 Sysfs ``alarms`` allow read or write TH and TL (Temperature High an Low) alarms. 94 Values shall be space separated and in the device range (typical -55 degC 95 to 125 degC). Values are integer as they are store in a 8bit register in 96 the device. Lowest value is automatically put to TL. Once set, alarms could 97 be search at master level. 98 99 The module parameter strong_pullup can be set to 0 to disable the 100 strong pullup, 1 to enable autodetection or 2 to force strong pullup. 101 In case of autodetection, the driver will use the "READ POWER SUPPLY" 102 command to check if there are pariste powered devices on the bus. 103 If so, it will activate the master's strong pullup. 104 In case the detection of parasite devices using this command fails 105 (seems to be the case with some DS18S20) the strong pullup can 106 be force-enabled. 107 108 If the strong pullup is enabled, the master's strong pullup will be 109 driven when the conversion is taking place, provided the master driver 110 does support the strong pullup (or it falls back to a pullup 111 resistor). The DS18b20 temperature sensor specification lists a 112 maximum current draw of 1.5mA and that a 5k pullup resistor is not 113 sufficient. The strong pullup is designed to provide the additional 114 current required. 115 116 The DS28EA00 provides an additional two pins for implementing a sequence 117 detection algorithm. This feature allows you to determine the physical 118 location of the chip in the 1-wire bus without needing pre-existing 119 knowledge of the bus ordering. Support is provided through the sysfs 120 ``w1_seq``. The file will contain a single line with an integer value 121 representing the device index in the bus starting at 0. 122 123 ``features`` sysfs entry controls optional driver settings per device. 124 Insufficient power in parasite mode, line noise and insufficient conversion 125 time may lead to conversion failure. Original DS18B20 and some clones allow for 126 detection of invalid conversion. Write bit mask ``1`` to ``features`` to enable 127 checking the conversion success. If byte 6 of scratchpad memory is 0xC after 128 conversion and temperature reads 85.00 (powerup value) or 127.94 (insufficient 129 power), the driver returns a conversion error. Bit mask ``2`` enables poll for 130 conversion completion (normal power only) by generating read cycles on the bus 131 after conversion starts. In parasite power mode this feature is not available. 132 Feature bit masks may be combined (OR). More details in 133 Documentation/ABI/testing/sysfs-driver-w1_therm 134 135 GX20MH01 device shares family number 0x28 with DS18*20. The device is generally 136 compatible with DS18B20. Added are lowest 2\ :sup:`-5`, 2\ :sup:`-6` temperature 137 bits in Config register; R2 bit in Config register enabling 13 and 14 bit 138 resolutions. The device is powered up in 14-bit resolution mode. The conversion 139 times specified in the datasheet are too low and have to be increased. The 140 device supports driver features ``1`` and ``2``. 141 142 MAX31850 device shares family number 0x3B with DS1825. The device is generally 143 compatible with DS1825. The higher 4 bits of Config register read all 1, 144 indicating 15, but the device is always operating in 14-bit resolution mode.
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