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R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +00001Kernel driver lm90
2==================
3
4Supported chips:
5 * National Semiconductor LM90
6 Prefix: '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
11 Prefix: 'lm99'
12 Addresses scanned: I2C 0x4c and 0x4d
13 Datasheet: Publicly available at the National Semiconductor website
Jean Delvarea874a102008-10-17 17:51:10 +020014 http://www.national.com/mpf/LM/LM89.html
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +000015 * National Semiconductor LM99
16 Prefix: '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
21 Prefix: 'lm86'
22 Addresses scanned: I2C 0x4c
23 Datasheet: Publicly available at the National Semiconductor website
Jean Delvarea874a102008-10-17 17:51:10 +020024 http://www.national.com/mpf/LM/LM86.html
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +000025 * Analog Devices ADM1032
26 Prefix: 'adm1032'
Jean Delvare90209b42005-10-26 22:20:21 +020027 Addresses scanned: I2C 0x4c and 0x4d
Jean Delvarea874a102008-10-17 17:51:10 +020028 Datasheet: Publicly available at the ON Semiconductor website
29 http://www.onsemi.com/PowerSolutions/product.do?id=ADM1032
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +000030 * Analog Devices ADT7461
31 Prefix: 'adt7461'
Jean Delvare90209b42005-10-26 22:20:21 +020032 Addresses scanned: I2C 0x4c and 0x4d
Jean Delvarea874a102008-10-17 17:51:10 +020033 Datasheet: Publicly available at the ON Semiconductor website
34 http://www.onsemi.com/PowerSolutions/product.do?id=ADT7461
Ben Hutchings271dabf2008-10-17 17:51:11 +020035 * Maxim MAX6646
36 Prefix: 'max6646'
37 Addresses scanned: I2C 0x4d
38 Datasheet: Publicly available at the Maxim website
39 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
40 * Maxim MAX6647
41 Prefix: 'max6646'
42 Addresses scanned: I2C 0x4e
43 Datasheet: Publicly available at the Maxim website
44 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
45 * Maxim MAX6649
46 Prefix: 'max6646'
47 Addresses scanned: I2C 0x4c
48 Datasheet: Publicly available at the Maxim website
49 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +000050 * Maxim MAX6657
51 Prefix: 'max6657'
52 Addresses scanned: I2C 0x4c
53 Datasheet: Publicly available at the Maxim website
54 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
55 * Maxim MAX6658
56 Prefix: 'max6657'
57 Addresses scanned: I2C 0x4c
58 Datasheet: Publicly available at the Maxim website
59 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
60 * Maxim MAX6659
61 Prefix: 'max6657'
62 Addresses scanned: I2C 0x4c, 0x4d (unsupported 0x4e)
63 Datasheet: Publicly available at the Maxim website
64 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
Rainer Birkenmaier32c82a92007-06-09 10:11:16 -040065 * Maxim MAX6680
66 Prefix: 'max6680'
67 Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
68 0x4c, 0x4d and 0x4e
69 Datasheet: Publicly available at the Maxim website
70 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
71 * Maxim MAX6681
72 Prefix: 'max6680'
73 Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
74 0x4c, 0x4d and 0x4e
75 Datasheet: Publicly available at the Maxim website
76 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +000077
78
79Author: Jean Delvare <khali@linux-fr.org>
80
81
82Description
83-----------
84
85The LM90 is a digital temperature sensor. It senses its own temperature as
86well as the temperature of up to one external diode. It is compatible
Nate Case23b2d472008-10-17 17:51:10 +020087with many other devices, many of which are supported by this driver.
Rainer Birkenmaier32c82a92007-06-09 10:11:16 -040088
89Note that there is no easy way to differentiate between the MAX6657,
90MAX6658 and MAX6659 variants. The extra address and features of the
91MAX6659 are not supported by this driver. The MAX6680 and MAX6681 only
92differ in their pinout, therefore they obviously can't (and don't need to)
Nate Case23b2d472008-10-17 17:51:10 +020093be distinguished.
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +000094
95The specificity of this family of chipsets over the ADM1021/LM84
96family is that it features critical limits with hysteresis, and an
97increased resolution of the remote temperature measurement.
98
99The different chipsets of the family are not strictly identical, although
Jean Delvaref65e1702008-10-17 17:51:09 +0200100very similar. For reference, here comes a non-exhaustive list of specific
101features:
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +0000102
103LM90:
104 * Filter and alert configuration register at 0xBF.
105 * ALERT is triggered by temperatures over critical limits.
106
107LM86 and LM89:
108 * Same as LM90
109 * Better external channel accuracy
110
111LM99:
112 * Same as LM89
113 * External temperature shifted by 16 degrees down
114
115ADM1032:
116 * Consecutive alert register at 0x22.
117 * Conversion averaging.
118 * Up to 64 conversions/s.
119 * ALERT is triggered by open remote sensor.
Jean Delvarec3df5802005-10-26 21:39:40 +0200120 * SMBus PEC support for Write Byte and Receive Byte transactions.
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +0000121
Rainer Birkenmaier32c82a92007-06-09 10:11:16 -0400122ADT7461:
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +0000123 * Extended temperature range (breaks compatibility)
124 * Lower resolution for remote temperature
125
126MAX6657 and MAX6658:
Jean Delvaref65e1702008-10-17 17:51:09 +0200127 * Better local resolution
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +0000128 * Remote sensor type selection
129
Rainer Birkenmaier32c82a92007-06-09 10:11:16 -0400130MAX6659:
Jean Delvaref65e1702008-10-17 17:51:09 +0200131 * Better local resolution
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +0000132 * Selectable address
133 * Second critical temperature limit
134 * Remote sensor type selection
135
Rainer Birkenmaier32c82a92007-06-09 10:11:16 -0400136MAX6680 and MAX6681:
137 * Selectable address
138 * Remote sensor type selection
139
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +0000140All temperature values are given in degrees Celsius. Resolution
141is 1.0 degree for the local temperature, 0.125 degree for the remote
Jean Delvaref65e1702008-10-17 17:51:09 +0200142temperature, except for the MAX6657, MAX6658 and MAX6659 which have a
143resolution of 0.125 degree for both temperatures.
R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +0000144
145Each sensor has its own high and low limits, plus a critical limit.
146Additionally, there is a relative hysteresis value common to both critical
147values. To make life easier to user-space applications, two absolute values
148are exported, one for each channel, but these values are of course linked.
149Only the local hysteresis can be set from user-space, and the same delta
150applies to the remote hysteresis.
151
152The lm90 driver will not update its values more frequently than every
153other second; reading them more often will do no harm, but will return
154'old' values.
155
Jean Delvarec3df5802005-10-26 21:39:40 +0200156PEC Support
157-----------
158
159The ADM1032 is the only chip of the family which supports PEC. It does
160not support PEC on all transactions though, so some care must be taken.
161
162When reading a register value, the PEC byte is computed and sent by the
163ADM1032 chip. However, in the case of a combined transaction (SMBus Read
164Byte), the ADM1032 computes the CRC value over only the second half of
165the message rather than its entirety, because it thinks the first half
166of the message belongs to a different transaction. As a result, the CRC
167value differs from what the SMBus master expects, and all reads fail.
168
169For this reason, the lm90 driver will enable PEC for the ADM1032 only if
170the bus supports the SMBus Send Byte and Receive Byte transaction types.
171These transactions will be used to read register values, instead of
172SMBus Read Byte, and PEC will work properly.
173
174Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
175Instead, it will try to write the PEC value to the register (because the
176SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
Jean Delvare09664152007-06-09 10:11:15 -0400177without PEC), which is not what we want. Thus, PEC is explicitly disabled
Jean Delvarec3df5802005-10-26 21:39:40 +0200178on SMBus Send Byte transactions in the lm90 driver.
179
180PEC on byte data transactions represents a significant increase in bandwidth
181usage (+33% for writes, +25% for reads) in normal conditions. With the need
182to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
183two transactions will typically mean twice as much delay waiting for
184transaction completion, effectively doubling the register cache refresh time.
185I guess reliability comes at a price, but it's quite expensive this time.
186
187So, as not everyone might enjoy the slowdown, PEC can be disabled through
188sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
189to that file to enable PEC again.