1 ====================== 1 ======================
2 Kernel driver w1_therm 2 Kernel driver w1_therm
3 ====================== 3 ======================
4 4
5 Supported chips: 5 Supported chips:
6 6
7 * Maxim ds18*20 based temperature sensors. 7 * Maxim ds18*20 based temperature sensors.
8 * Maxim ds1825 based temperature sensors. 8 * Maxim ds1825 based temperature sensors.
9 * GXCAS GX20MH01 temperature sensor. 9 * GXCAS GX20MH01 temperature sensor.
10 * Maxim MAX31850 thermoelement interface. 10 * Maxim MAX31850 thermoelement interface.
11 11
12 Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru> 12 Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
13 13
14 14
15 Description 15 Description
16 ----------- 16 -----------
17 17
18 w1_therm provides basic temperature conversion 18 w1_therm provides basic temperature conversion for ds18*20, ds28ea00, GX20MH01
19 and MAX31850 devices. 19 and MAX31850 devices.
20 20
21 Supported family codes: 21 Supported family codes:
22 22
23 ==================== ==== 23 ==================== ====
24 W1_THERM_DS18S20 0x10 24 W1_THERM_DS18S20 0x10
25 W1_THERM_DS1822 0x22 25 W1_THERM_DS1822 0x22
26 W1_THERM_DS18B20 0x28 26 W1_THERM_DS18B20 0x28
27 W1_THERM_DS1825 0x3B 27 W1_THERM_DS1825 0x3B
28 W1_THERM_DS28EA00 0x42 28 W1_THERM_DS28EA00 0x42
29 ==================== ==== 29 ==================== ====
30 30
31 Support is provided through the sysfs entry `` 31 Support is provided through the sysfs entry ``w1_slave``. Each open and
32 read sequence will initiate a temperature conv 32 read sequence will initiate a temperature conversion, then provide two
33 lines of ASCII output. The first line contains 33 lines of ASCII output. The first line contains the nine hex bytes
34 read along with a calculated crc value and YES 34 read along with a calculated crc value and YES or NO if it matched.
35 If the crc matched the returned values are ret 35 If the crc matched the returned values are retained. The second line
36 displays the retained values along with a temp 36 displays the retained values along with a temperature in millidegrees
37 Centigrade after t=. 37 Centigrade after t=.
38 38
39 Alternatively, temperature can be read using ` 39 Alternatively, temperature can be read using ``temperature`` sysfs, it
40 returns only the temperature in millidegrees C 40 returns only the temperature in millidegrees Centigrade.
41 41
42 A bulk read of all devices on the bus could be 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 43 to ``therm_bulk_read`` entry at w1_bus_master level. This will
44 send the convert command to all devices on the 44 send the convert command to all devices on the bus, and if parasite
45 powered devices are detected on the bus (and s 45 powered devices are detected on the bus (and strong pullup is enabled
46 in the module), it will drive the line high du 46 in the module), it will drive the line high during the longer conversion
47 time required by parasited powered device on t 47 time required by parasited powered device on the line. Reading
48 ``therm_bulk_read`` will return 0 if no bulk c 48 ``therm_bulk_read`` will return 0 if no bulk conversion pending,
49 -1 if at least one sensor still in conversion, 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 rea 50 but at least one sensor value has not been read yet. Result temperature is
51 then accessed by reading the ``temperature`` e 51 then accessed by reading the ``temperature`` entry of each device, which
52 may return empty if conversion is still in pro 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 immedi 53 read is sent but one sensor is not read immediately, the next access to
54 ``temperature`` on this device will return the 54 ``temperature`` on this device will return the temperature measured at the
55 time of issue of the bulk read command (not th 55 time of issue of the bulk read command (not the current temperature).
56 56
57 A strong pullup will be applied during the con 57 A strong pullup will be applied during the conversion if required.
58 58
59 ``conv_time`` is used to get current conversio 59 ``conv_time`` is used to get current conversion time (read), and
60 adjust it (write). A temperature conversion ti 60 adjust it (write). A temperature conversion time depends on the device type and
61 its current resolution. Default conversion tim 61 its current resolution. Default conversion time is set by the driver according
62 to the device datasheet. A conversion time for 62 to the device datasheet. A conversion time for many original device clones
63 deviate from datasheet specs. There are three 63 deviate from datasheet specs. There are three options: 1) manually set the
64 correct conversion time by writing a value in 64 correct conversion time by writing a value in milliseconds to ``conv_time``; 2)
65 auto measure and set a conversion time by writ 65 auto measure and set a conversion time by writing ``1`` to
66 ``conv_time``; 3) use ``features`` to enable p 66 ``conv_time``; 3) use ``features`` to enable poll for conversion
67 completion. Options 2, 3 can't be used in para 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 ``c 68 the default conversion time write ``0`` to ``conv_time``.
69 69
70 Writing a resolution value (in bits) to ``w1_s 70 Writing a resolution value (in bits) to ``w1_slave`` will change the
71 precision of the sensor for the next readings. 71 precision of the sensor for the next readings. Allowed resolutions are defined by
72 the sensor. Resolution is reset when the senso 72 the sensor. Resolution is reset when the sensor gets power-cycled.
73 73
74 To store the current resolution in EEPROM, wri 74 To store the current resolution in EEPROM, write ``0`` to ``w1_slave``.
75 Since the EEPROM has a limited amount of write 75 Since the EEPROM has a limited amount of writes (>50k), this command should be
76 used wisely. 76 used wisely.
77 77
78 Alternatively, resolution can be read or writt 78 Alternatively, resolution can be read or written using the dedicated
79 ``resolution`` entry on each device, if suppor 79 ``resolution`` entry on each device, if supported by the sensor.
80 80
81 Some non-genuine DS18B20 chips are fixed in 12 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 veri 82 resolution is read back from the chip and verified.
83 83
84 Note: Changing the resolution reverts the conv 84 Note: Changing the resolution reverts the conversion time to default.
85 85
86 The write-only sysfs entry ``eeprom_cmd`` is a 86 The write-only sysfs entry ``eeprom_cmd`` is an alternative for EEPROM operations.
87 Write ``save`` to save device RAM to EEPROM. W 87 Write ``save`` to save device RAM to EEPROM. Write ``restore`` to restore EEPROM
88 data in device RAM. 88 data in device RAM.
89 89
90 ``ext_power`` entry allows checking the power 90 ``ext_power`` entry allows checking the power state of each device. Reads
91 ``0`` if the device is parasite powered, ``1`` 91 ``0`` if the device is parasite powered, ``1`` if the device is externally powered.
92 92
93 Sysfs ``alarms`` allow read or write TH and TL 93 Sysfs ``alarms`` allow read or write TH and TL (Temperature High an Low) alarms.
94 Values shall be space separated and in the dev 94 Values shall be space separated and in the device range (typical -55 degC
95 to 125 degC). Values are integer as they are s 95 to 125 degC). Values are integer as they are store in a 8bit register in
96 the device. Lowest value is automatically put 96 the device. Lowest value is automatically put to TL. Once set, alarms could
97 be search at master level. 97 be search at master level.
98 98
99 The module parameter strong_pullup can be set 99 The module parameter strong_pullup can be set to 0 to disable the
100 strong pullup, 1 to enable autodetection or 2 100 strong pullup, 1 to enable autodetection or 2 to force strong pullup.
101 In case of autodetection, the driver will use 101 In case of autodetection, the driver will use the "READ POWER SUPPLY"
102 command to check if there are pariste powered 102 command to check if there are pariste powered devices on the bus.
103 If so, it will activate the master's strong pu 103 If so, it will activate the master's strong pullup.
104 In case the detection of parasite devices usin 104 In case the detection of parasite devices using this command fails
105 (seems to be the case with some DS18S20) the s 105 (seems to be the case with some DS18S20) the strong pullup can
106 be force-enabled. 106 be force-enabled.
107 107
108 If the strong pullup is enabled, the master's 108 If the strong pullup is enabled, the master's strong pullup will be
109 driven when the conversion is taking place, pr 109 driven when the conversion is taking place, provided the master driver
110 does support the strong pullup (or it falls ba 110 does support the strong pullup (or it falls back to a pullup
111 resistor). The DS18b20 temperature sensor spe 111 resistor). The DS18b20 temperature sensor specification lists a
112 maximum current draw of 1.5mA and that a 5k pu 112 maximum current draw of 1.5mA and that a 5k pullup resistor is not
113 sufficient. The strong pullup is designed to 113 sufficient. The strong pullup is designed to provide the additional
114 current required. 114 current required.
115 115
116 The DS28EA00 provides an additional two pins f 116 The DS28EA00 provides an additional two pins for implementing a sequence
117 detection algorithm. This feature allows you 117 detection algorithm. This feature allows you to determine the physical
118 location of the chip in the 1-wire bus without 118 location of the chip in the 1-wire bus without needing pre-existing
119 knowledge of the bus ordering. Support is pro 119 knowledge of the bus ordering. Support is provided through the sysfs
120 ``w1_seq``. The file will contain a single lin 120 ``w1_seq``. The file will contain a single line with an integer value
121 representing the device index in the bus start 121 representing the device index in the bus starting at 0.
122 122
123 ``features`` sysfs entry controls optional dri 123 ``features`` sysfs entry controls optional driver settings per device.
124 Insufficient power in parasite mode, line nois 124 Insufficient power in parasite mode, line noise and insufficient conversion
125 time may lead to conversion failure. Original 125 time may lead to conversion failure. Original DS18B20 and some clones allow for
126 detection of invalid conversion. Write bit mas 126 detection of invalid conversion. Write bit mask ``1`` to ``features`` to enable
127 checking the conversion success. If byte 6 of 127 checking the conversion success. If byte 6 of scratchpad memory is 0xC after
128 conversion and temperature reads 85.00 (poweru 128 conversion and temperature reads 85.00 (powerup value) or 127.94 (insufficient
129 power), the driver returns a conversion error. 129 power), the driver returns a conversion error. Bit mask ``2`` enables poll for
130 conversion completion (normal power only) by g 130 conversion completion (normal power only) by generating read cycles on the bus
131 after conversion starts. In parasite power mod 131 after conversion starts. In parasite power mode this feature is not available.
132 Feature bit masks may be combined (OR). More d 132 Feature bit masks may be combined (OR). More details in
133 Documentation/ABI/testing/sysfs-driver-w1_ther 133 Documentation/ABI/testing/sysfs-driver-w1_therm
134 134
135 GX20MH01 device shares family number 0x28 with 135 GX20MH01 device shares family number 0x28 with DS18*20. The device is generally
136 compatible with DS18B20. Added are lowest 2\ : 136 compatible with DS18B20. Added are lowest 2\ :sup:`-5`, 2\ :sup:`-6` temperature
137 bits in Config register; R2 bit in Config regi 137 bits in Config register; R2 bit in Config register enabling 13 and 14 bit
138 resolutions. The device is powered up in 14-bi 138 resolutions. The device is powered up in 14-bit resolution mode. The conversion
139 times specified in the datasheet are too low a 139 times specified in the datasheet are too low and have to be increased. The
140 device supports driver features ``1`` and ``2` 140 device supports driver features ``1`` and ``2``.
141 141
142 MAX31850 device shares family number 0x3B with 142 MAX31850 device shares family number 0x3B with DS1825. The device is generally
143 compatible with DS1825. The higher 4 bits of C 143 compatible with DS1825. The higher 4 bits of Config register read all 1,
144 indicating 15, but the device is always operat 144 indicating 15, but the device is always operating in 14-bit resolution mode.
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