Based on kernel version 2.6.33. Page generated on 2010-02-24 15:36 EST.
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: 'lm89' (no auto-detection) 12 Addresses scanned: I2C 0x4c and 0x4d 13 Datasheet: Publicly available at the National Semiconductor website 14 http://www.national.com/mpf/LM/LM89.html 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 24 http://www.national.com/mpf/LM/LM86.html 25 * Analog Devices ADM1032 26 Prefix: 'adm1032' 27 Addresses scanned: I2C 0x4c and 0x4d 28 Datasheet: Publicly available at the ON Semiconductor website 29 http://www.onsemi.com/PowerSolutions/product.do?id=ADM1032 30 * Analog Devices ADT7461 31 Prefix: 'adt7461' 32 Addresses scanned: I2C 0x4c and 0x4d 33 Datasheet: Publicly available at the ON Semiconductor website 34 http://www.onsemi.com/PowerSolutions/product.do?id=ADT7461 35 * 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 MAX6648 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/3500 50 * Maxim MAX6649 51 Prefix: 'max6646' 52 Addresses scanned: I2C 0x4c 53 Datasheet: Publicly available at the Maxim website 54 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497 55 * Maxim MAX6657 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 MAX6658 61 Prefix: 'max6657' 62 Addresses scanned: I2C 0x4c 63 Datasheet: Publicly available at the Maxim website 64 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578 65 * Maxim MAX6659 66 Prefix: 'max6657' 67 Addresses scanned: I2C 0x4c, 0x4d (unsupported 0x4e) 68 Datasheet: Publicly available at the Maxim website 69 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578 70 * Maxim MAX6680 71 Prefix: 'max6680' 72 Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b, 73 0x4c, 0x4d and 0x4e 74 Datasheet: Publicly available at the Maxim website 75 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370 76 * Maxim MAX6681 77 Prefix: 'max6680' 78 Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b, 79 0x4c, 0x4d and 0x4e 80 Datasheet: Publicly available at the Maxim website 81 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370 82 * Maxim MAX6692 83 Prefix: 'max6646' 84 Addresses scanned: I2C 0x4c 85 Datasheet: Publicly available at the Maxim website 86 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500 87 88 89 Author: Jean Delvare <khali[AT]linux-fr[DOT]org> 90 91 92 Description 93 ----------- 94 95 The LM90 is a digital temperature sensor. It senses its own temperature as 96 well as the temperature of up to one external diode. It is compatible 97 with many other devices, many of which are supported by this driver. 98 99 Note that there is no easy way to differentiate between the MAX6657, 100 MAX6658 and MAX6659 variants. The extra address and features of the 101 MAX6659 are not supported by this driver. The MAX6680 and MAX6681 only 102 differ in their pinout, therefore they obviously can't (and don't need to) 103 be distinguished. 104 105 The specificity of this family of chipsets over the ADM1021/LM84 106 family is that it features critical limits with hysteresis, and an 107 increased resolution of the remote temperature measurement. 108 109 The different chipsets of the family are not strictly identical, although 110 very similar. For reference, here comes a non-exhaustive list of specific 111 features: 112 113 LM90: 114 * Filter and alert configuration register at 0xBF. 115 * ALERT is triggered by temperatures over critical limits. 116 117 LM86 and LM89: 118 * Same as LM90 119 * Better external channel accuracy 120 121 LM99: 122 * Same as LM89 123 * External temperature shifted by 16 degrees down 124 125 ADM1032: 126 * Consecutive alert register at 0x22. 127 * Conversion averaging. 128 * Up to 64 conversions/s. 129 * ALERT is triggered by open remote sensor. 130 * SMBus PEC support for Write Byte and Receive Byte transactions. 131 132 ADT7461: 133 * Extended temperature range (breaks compatibility) 134 * Lower resolution for remote temperature 135 136 MAX6657 and MAX6658: 137 * Better local resolution 138 * Remote sensor type selection 139 140 MAX6659: 141 * Better local resolution 142 * Selectable address 143 * Second critical temperature limit 144 * Remote sensor type selection 145 146 MAX6680 and MAX6681: 147 * Selectable address 148 * Remote sensor type selection 149 150 All temperature values are given in degrees Celsius. Resolution 151 is 1.0 degree for the local temperature, 0.125 degree for the remote 152 temperature, except for the MAX6657, MAX6658 and MAX6659 which have a 153 resolution of 0.125 degree for both temperatures. 154 155 Each sensor has its own high and low limits, plus a critical limit. 156 Additionally, there is a relative hysteresis value common to both critical 157 values. To make life easier to user-space applications, two absolute values 158 are exported, one for each channel, but these values are of course linked. 159 Only the local hysteresis can be set from user-space, and the same delta 160 applies to the remote hysteresis. 161 162 The lm90 driver will not update its values more frequently than every 163 other second; reading them more often will do no harm, but will return 164 'old' values. 165 166 PEC Support 167 ----------- 168 169 The ADM1032 is the only chip of the family which supports PEC. It does 170 not support PEC on all transactions though, so some care must be taken. 171 172 When reading a register value, the PEC byte is computed and sent by the 173 ADM1032 chip. However, in the case of a combined transaction (SMBus Read 174 Byte), the ADM1032 computes the CRC value over only the second half of 175 the message rather than its entirety, because it thinks the first half 176 of the message belongs to a different transaction. As a result, the CRC 177 value differs from what the SMBus master expects, and all reads fail. 178 179 For this reason, the lm90 driver will enable PEC for the ADM1032 only if 180 the bus supports the SMBus Send Byte and Receive Byte transaction types. 181 These transactions will be used to read register values, instead of 182 SMBus Read Byte, and PEC will work properly. 183 184 Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC. 185 Instead, it will try to write the PEC value to the register (because the 186 SMBus Send Byte transaction with PEC is similar to a Write Byte transaction 187 without PEC), which is not what we want. Thus, PEC is explicitly disabled 188 on SMBus Send Byte transactions in the lm90 driver. 189 190 PEC on byte data transactions represents a significant increase in bandwidth 191 usage (+33% for writes, +25% for reads) in normal conditions. With the need 192 to use two SMBus transaction for reads, this overhead jumps to +50%. Worse, 193 two transactions will typically mean twice as much delay waiting for 194 transaction completion, effectively doubling the register cache refresh time. 195 I guess reliability comes at a price, but it's quite expensive this time. 196 197 So, as not everyone might enjoy the slowdown, PEC can be disabled through 198 sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1 199 to that file to enable PEC again.