1Kernel 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: '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 * Winbond/Nuvoton W83L771AWG/ASG 88 Prefix: 'w83l771' 89 Addresses scanned: I2C 0x4c 90 Datasheet: Not publicly available, can be requested from Nuvoton 91 92 93Author: Jean Delvare <khali@linux-fr.org> 94 95 96Description 97----------- 98 99The LM90 is a digital temperature sensor. It senses its own temperature as 100well as the temperature of up to one external diode. It is compatible 101with many other devices, many of which are supported by this driver. 102 103Note that there is no easy way to differentiate between the MAX6657, 104MAX6658 and MAX6659 variants. The extra address and features of the 105MAX6659 are not supported by this driver. The MAX6680 and MAX6681 only 106differ in their pinout, therefore they obviously can't (and don't need to) 107be distinguished. 108 109The specificity of this family of chipsets over the ADM1021/LM84 110family is that it features critical limits with hysteresis, and an 111increased resolution of the remote temperature measurement. 112 113The different chipsets of the family are not strictly identical, although 114very similar. For reference, here comes a non-exhaustive list of specific 115features: 116 117LM90: 118 * Filter and alert configuration register at 0xBF. 119 * ALERT is triggered by temperatures over critical limits. 120 121LM86 and LM89: 122 * Same as LM90 123 * Better external channel accuracy 124 125LM99: 126 * Same as LM89 127 * External temperature shifted by 16 degrees down 128 129ADM1032: 130 * Consecutive alert register at 0x22. 131 * Conversion averaging. 132 * Up to 64 conversions/s. 133 * ALERT is triggered by open remote sensor. 134 * SMBus PEC support for Write Byte and Receive Byte transactions. 135 136ADT7461: 137 * Extended temperature range (breaks compatibility) 138 * Lower resolution for remote temperature 139 140MAX6657 and MAX6658: 141 * Better local resolution 142 * Remote sensor type selection 143 144MAX6659: 145 * Better local resolution 146 * Selectable address 147 * Second critical temperature limit 148 * Remote sensor type selection 149 150MAX6680 and MAX6681: 151 * Selectable address 152 * Remote sensor type selection 153 154W83L771AWG/ASG 155 * The AWG and ASG variants only differ in package format. 156 * Filter and alert configuration register at 0xBF 157 * Diode ideality factor configuration (remote sensor) at 0xE3 158 * Moving average (depending on conversion rate) 159 160All temperature values are given in degrees Celsius. Resolution 161is 1.0 degree for the local temperature, 0.125 degree for the remote 162temperature, except for the MAX6657, MAX6658 and MAX6659 which have a 163resolution of 0.125 degree for both temperatures. 164 165Each sensor has its own high and low limits, plus a critical limit. 166Additionally, there is a relative hysteresis value common to both critical 167values. To make life easier to user-space applications, two absolute values 168are exported, one for each channel, but these values are of course linked. 169Only the local hysteresis can be set from user-space, and the same delta 170applies to the remote hysteresis. 171 172The lm90 driver will not update its values more frequently than every 173other second; reading them more often will do no harm, but will return 174'old' values. 175 176SMBus Alert Support 177------------------- 178 179This driver has basic support for SMBus alert. When an alert is received, 180the status register is read and the faulty temperature channel is logged. 181 182The Analog Devices chips (ADM1032 and ADT7461) do not implement the SMBus 183alert protocol properly so additional care is needed: the ALERT output is 184disabled when an alert is received, and is re-enabled only when the alarm 185is gone. Otherwise the chip would block alerts from other chips in the bus 186as long as the alarm is active. 187 188PEC Support 189----------- 190 191The ADM1032 is the only chip of the family which supports PEC. It does 192not support PEC on all transactions though, so some care must be taken. 193 194When reading a register value, the PEC byte is computed and sent by the 195ADM1032 chip. However, in the case of a combined transaction (SMBus Read 196Byte), the ADM1032 computes the CRC value over only the second half of 197the message rather than its entirety, because it thinks the first half 198of the message belongs to a different transaction. As a result, the CRC 199value differs from what the SMBus master expects, and all reads fail. 200 201For this reason, the lm90 driver will enable PEC for the ADM1032 only if 202the bus supports the SMBus Send Byte and Receive Byte transaction types. 203These transactions will be used to read register values, instead of 204SMBus Read Byte, and PEC will work properly. 205 206Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC. 207Instead, it will try to write the PEC value to the register (because the 208SMBus Send Byte transaction with PEC is similar to a Write Byte transaction 209without PEC), which is not what we want. Thus, PEC is explicitly disabled 210on SMBus Send Byte transactions in the lm90 driver. 211 212PEC on byte data transactions represents a significant increase in bandwidth 213usage (+33% for writes, +25% for reads) in normal conditions. With the need 214to use two SMBus transaction for reads, this overhead jumps to +50%. Worse, 215two transactions will typically mean twice as much delay waiting for 216transaction completion, effectively doubling the register cache refresh time. 217I guess reliability comes at a price, but it's quite expensive this time. 218 219So, as not everyone might enjoy the slowdown, PEC can be disabled through 220sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1 221to that file to enable PEC again. 222