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1 | Kernel driver lm90 |
2 | ================== | |
3 | ||
4 | Supported 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 | |
a874a10c | 14 | http://www.national.com/mpf/LM/LM89.html |
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15 | * 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 | |
a874a10c | 24 | http://www.national.com/mpf/LM/LM86.html |
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25 | * Analog Devices ADM1032 |
26 | Prefix: 'adm1032' | |
90209b42 | 27 | Addresses scanned: I2C 0x4c and 0x4d |
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28 | Datasheet: Publicly available at the ON Semiconductor website |
29 | http://www.onsemi.com/PowerSolutions/product.do?id=ADM1032 | |
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30 | * Analog Devices ADT7461 |
31 | Prefix: 'adt7461' | |
90209b42 | 32 | Addresses scanned: I2C 0x4c and 0x4d |
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33 | Datasheet: Publicly available at the ON Semiconductor website |
34 | http://www.onsemi.com/PowerSolutions/product.do?id=ADT7461 | |
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35 | Note: Only if in ADM1032 compatibility mode |
36 | * Maxim MAX6657 | |
37 | Prefix: 'max6657' | |
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 | |
41 | * Maxim MAX6658 | |
42 | Prefix: 'max6657' | |
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 | |
46 | * Maxim MAX6659 | |
47 | Prefix: 'max6657' | |
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 | |
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51 | * Maxim MAX6680 |
52 | Prefix: 'max6680' | |
53 | Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b, | |
54 | 0x4c, 0x4d and 0x4e | |
55 | Datasheet: Publicly available at the Maxim website | |
56 | http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370 | |
57 | * Maxim MAX6681 | |
58 | Prefix: 'max6680' | |
59 | Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b, | |
60 | 0x4c, 0x4d and 0x4e | |
61 | Datasheet: Publicly available at the Maxim website | |
62 | http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370 | |
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63 | |
64 | ||
65 | Author: Jean Delvare <khali@linux-fr.org> | |
66 | ||
67 | ||
68 | Description | |
69 | ----------- | |
70 | ||
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, | |
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74 | the MAX6657, MAX6658, MAX6659, MAX6680 and the MAX6681 all of which are |
75 | supported by this driver. | |
76 | ||
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. | |
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83 | |
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. | |
87 | ||
88 | The different chipsets of the family are not strictly identical, although | |
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89 | very similar. For reference, here comes a non-exhaustive list of specific |
90 | features: | |
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91 | |
92 | LM90: | |
93 | * Filter and alert configuration register at 0xBF. | |
94 | * ALERT is triggered by temperatures over critical limits. | |
95 | ||
96 | LM86 and LM89: | |
97 | * Same as LM90 | |
98 | * Better external channel accuracy | |
99 | ||
100 | LM99: | |
101 | * Same as LM89 | |
102 | * External temperature shifted by 16 degrees down | |
103 | ||
104 | ADM1032: | |
105 | * Consecutive alert register at 0x22. | |
106 | * Conversion averaging. | |
107 | * Up to 64 conversions/s. | |
108 | * ALERT is triggered by open remote sensor. | |
c3df5806 | 109 | * SMBus PEC support for Write Byte and Receive Byte transactions. |
7f15b664 | 110 | |
32c82a93 | 111 | ADT7461: |
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112 | * Extended temperature range (breaks compatibility) |
113 | * Lower resolution for remote temperature | |
114 | ||
115 | MAX6657 and MAX6658: | |
f65e1708 | 116 | * Better local resolution |
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117 | * Remote sensor type selection |
118 | ||
32c82a93 | 119 | MAX6659: |
f65e1708 | 120 | * Better local resolution |
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121 | * Selectable address |
122 | * Second critical temperature limit | |
123 | * Remote sensor type selection | |
124 | ||
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125 | MAX6680 and MAX6681: |
126 | * Selectable address | |
127 | * Remote sensor type selection | |
128 | ||
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129 | All temperature values are given in degrees Celsius. Resolution |
130 | is 1.0 degree for the local temperature, 0.125 degree for the remote | |
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131 | temperature, except for the MAX6657, MAX6658 and MAX6659 which have a |
132 | resolution of 0.125 degree for both temperatures. | |
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133 | |
134 | Each sensor has its own high and low limits, plus a critical limit. | |
135 | Additionally, there is a relative hysteresis value common to both critical | |
136 | values. To make life easier to user-space applications, two absolute values | |
137 | are exported, one for each channel, but these values are of course linked. | |
138 | Only the local hysteresis can be set from user-space, and the same delta | |
139 | applies to the remote hysteresis. | |
140 | ||
141 | The lm90 driver will not update its values more frequently than every | |
142 | other second; reading them more often will do no harm, but will return | |
143 | 'old' values. | |
144 | ||
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145 | PEC Support |
146 | ----------- | |
147 | ||
148 | The ADM1032 is the only chip of the family which supports PEC. It does | |
149 | not support PEC on all transactions though, so some care must be taken. | |
150 | ||
151 | When reading a register value, the PEC byte is computed and sent by the | |
152 | ADM1032 chip. However, in the case of a combined transaction (SMBus Read | |
153 | Byte), the ADM1032 computes the CRC value over only the second half of | |
154 | the message rather than its entirety, because it thinks the first half | |
155 | of the message belongs to a different transaction. As a result, the CRC | |
156 | value differs from what the SMBus master expects, and all reads fail. | |
157 | ||
158 | For this reason, the lm90 driver will enable PEC for the ADM1032 only if | |
159 | the bus supports the SMBus Send Byte and Receive Byte transaction types. | |
160 | These transactions will be used to read register values, instead of | |
161 | SMBus Read Byte, and PEC will work properly. | |
162 | ||
163 | Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC. | |
164 | Instead, it will try to write the PEC value to the register (because the | |
165 | SMBus Send Byte transaction with PEC is similar to a Write Byte transaction | |
0966415d | 166 | without PEC), which is not what we want. Thus, PEC is explicitly disabled |
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167 | on SMBus Send Byte transactions in the lm90 driver. |
168 | ||
169 | PEC on byte data transactions represents a significant increase in bandwidth | |
170 | usage (+33% for writes, +25% for reads) in normal conditions. With the need | |
171 | to use two SMBus transaction for reads, this overhead jumps to +50%. Worse, | |
172 | two transactions will typically mean twice as much delay waiting for | |
173 | transaction completion, effectively doubling the register cache refresh time. | |
174 | I guess reliability comes at a price, but it's quite expensive this time. | |
175 | ||
176 | So, as not everyone might enjoy the slowdown, PEC can be disabled through | |
177 | sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1 | |
178 | to that file to enable PEC again. |