5 * National Semiconductor LM90
7 Addresses scanned: I2C 0x4c
8 Datasheet: Publicly available at the National Semiconductor website
9 http://www.national.com/pf/LM/LM90.html
10 * National Semiconductor LM89
12 Addresses scanned: I2C 0x4c and 0x4d
13 Datasheet: Publicly available at the National Semiconductor website
14 http://www.national.com/pf/LM/LM89.html
15 * National Semiconductor LM99
17 Addresses scanned: I2C 0x4c and 0x4d
18 Datasheet: Publicly available at the National Semiconductor website
19 http://www.national.com/pf/LM/LM99.html
20 * National Semiconductor LM86
22 Addresses scanned: I2C 0x4c
23 Datasheet: Publicly available at the National Semiconductor website
24 http://www.national.com/pf/LM/LM86.html
25 * Analog Devices ADM1032
27 Addresses scanned: I2C 0x4c and 0x4d
28 Datasheet: Publicly available at the Analog Devices website
29 http://www.analog.com/en/prod/0,2877,ADM1032,00.html
30 * Analog Devices ADT7461
32 Addresses scanned: I2C 0x4c and 0x4d
33 Datasheet: Publicly available at the Analog Devices website
34 http://www.analog.com/en/prod/0,2877,ADT7461,00.html
35 Note: Only if in ADM1032 compatibility mode
38 Addresses scanned: I2C 0x4c
39 Datasheet: Publicly available at the Maxim website
40 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
43 Addresses scanned: I2C 0x4c
44 Datasheet: Publicly available at the Maxim website
45 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
48 Addresses scanned: I2C 0x4c, 0x4d (unsupported 0x4e)
49 Datasheet: Publicly available at the Maxim website
50 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
53 Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
55 Datasheet: Publicly available at the Maxim website
56 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
59 Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
61 Datasheet: Publicly available at the Maxim website
62 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
65 Author: Jean Delvare <khali@linux-fr.org>
71 The LM90 is a digital temperature sensor. It senses its own temperature as
72 well as the temperature of up to one external diode. It is compatible
73 with many other devices such as the LM86, the LM89, the LM99, the ADM1032,
74 the MAX6657, MAX6658, MAX6659, MAX6680 and the MAX6681 all of which are
75 supported by this driver.
77 Note that there is no easy way to differentiate between the MAX6657,
78 MAX6658 and MAX6659 variants. The extra address and features of the
79 MAX6659 are not supported by this driver. The MAX6680 and MAX6681 only
80 differ in their pinout, therefore they obviously can't (and don't need to)
81 be distinguished. Additionally, the ADT7461 is supported if found in
82 ADM1032 compatibility mode.
84 The specificity of this family of chipsets over the ADM1021/LM84
85 family is that it features critical limits with hysteresis, and an
86 increased resolution of the remote temperature measurement.
88 The different chipsets of the family are not strictly identical, although
89 very similar. This driver doesn't handle any specific feature for now,
90 with the exception of SMBus PEC. For reference, here comes a non-exhaustive
91 list of specific features:
94 * Filter and alert configuration register at 0xBF.
95 * ALERT is triggered by temperatures over critical limits.
99 * Better external channel accuracy
103 * External temperature shifted by 16 degrees down
106 * Consecutive alert register at 0x22.
107 * Conversion averaging.
108 * Up to 64 conversions/s.
109 * ALERT is triggered by open remote sensor.
110 * SMBus PEC support for Write Byte and Receive Byte transactions.
113 * Extended temperature range (breaks compatibility)
114 * Lower resolution for remote temperature
117 * Remote sensor type selection
121 * Second critical temperature limit
122 * Remote sensor type selection
126 * Remote sensor type selection
128 All temperature values are given in degrees Celsius. Resolution
129 is 1.0 degree for the local temperature, 0.125 degree for the remote
132 Each sensor has its own high and low limits, plus a critical limit.
133 Additionally, there is a relative hysteresis value common to both critical
134 values. To make life easier to user-space applications, two absolute values
135 are exported, one for each channel, but these values are of course linked.
136 Only the local hysteresis can be set from user-space, and the same delta
137 applies to the remote hysteresis.
139 The lm90 driver will not update its values more frequently than every
140 other second; reading them more often will do no harm, but will return
146 The ADM1032 is the only chip of the family which supports PEC. It does
147 not support PEC on all transactions though, so some care must be taken.
149 When reading a register value, the PEC byte is computed and sent by the
150 ADM1032 chip. However, in the case of a combined transaction (SMBus Read
151 Byte), the ADM1032 computes the CRC value over only the second half of
152 the message rather than its entirety, because it thinks the first half
153 of the message belongs to a different transaction. As a result, the CRC
154 value differs from what the SMBus master expects, and all reads fail.
156 For this reason, the lm90 driver will enable PEC for the ADM1032 only if
157 the bus supports the SMBus Send Byte and Receive Byte transaction types.
158 These transactions will be used to read register values, instead of
159 SMBus Read Byte, and PEC will work properly.
161 Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
162 Instead, it will try to write the PEC value to the register (because the
163 SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
164 without PEC), which is not what we want. Thus, PEC is explicitly disabled
165 on SMBus Send Byte transactions in the lm90 driver.
167 PEC on byte data transactions represents a significant increase in bandwidth
168 usage (+33% for writes, +25% for reads) in normal conditions. With the need
169 to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
170 two transactions will typically mean twice as much delay waiting for
171 transaction completion, effectively doubling the register cache refresh time.
172 I guess reliability comes at a price, but it's quite expensive this time.
174 So, as not everyone might enjoy the slowdown, PEC can be disabled through
175 sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
176 to that file to enable PEC again.