Documentation/hwmon/lm90

   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   * Analog Devices ADT7461A
  36     Prefix: 'adt7461a'
  37     Addresses scanned: I2C 0x4c and 0x4d
  38     Datasheet: Publicly available at the ON Semiconductor website
  39                http://www.onsemi.com/PowerSolutions/product.do?id=ADT7461A
  40   * ON Semiconductor NCT1008
  41     Prefix: 'nct1008'
  42     Addresses scanned: I2C 0x4c and 0x4d
  43     Datasheet: Publicly available at the ON Semiconductor website
  44                http://www.onsemi.com/PowerSolutions/product.do?id=NCT1008
  45   * Maxim MAX6646
  46     Prefix: 'max6646'
  47     Addresses scanned: I2C 0x4d
  48     Datasheet: Publicly available at the Maxim website
  49                http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
  50   * Maxim MAX6647
  51     Prefix: 'max6646'
  52     Addresses scanned: I2C 0x4e
  53     Datasheet: Publicly available at the Maxim website
  54                http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
  55   * Maxim MAX6648
  56     Prefix: 'max6646'
  57     Addresses scanned: I2C 0x4c
  58     Datasheet: Publicly available at the Maxim website
  59                http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500
  60   * Maxim MAX6649
  61     Prefix: 'max6646'
  62     Addresses scanned: I2C 0x4c
  63     Datasheet: Publicly available at the Maxim website
  64                http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
  65   * Maxim MAX6657
  66     Prefix: 'max6657'
  67     Addresses scanned: I2C 0x4c
  68     Datasheet: Publicly available at the Maxim website
  69                http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
  70   * Maxim MAX6658
  71     Prefix: 'max6657'
  72     Addresses scanned: I2C 0x4c
  73     Datasheet: Publicly available at the Maxim website
  74                http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
  75   * Maxim MAX6659
  76     Prefix: 'max6659'
  77     Addresses scanned: I2C 0x4c, 0x4d, 0x4e
  78     Datasheet: Publicly available at the Maxim website
  79                http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
  80   * Maxim MAX6680
  81     Prefix: 'max6680'
  82     Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
  83                            0x4c, 0x4d and 0x4e
  84     Datasheet: Publicly available at the Maxim website
  85                http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
  86   * Maxim MAX6681
  87     Prefix: 'max6680'
  88     Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
  89                            0x4c, 0x4d and 0x4e
  90     Datasheet: Publicly available at the Maxim website
  91                http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
  92   * Maxim MAX6692
  93     Prefix: 'max6646'
  94     Addresses scanned: I2C 0x4c
  95     Datasheet: Publicly available at the Maxim website
  96                http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500
  97   * Maxim MAX6695
  98     Prefix: 'max6695'
  99     Addresses scanned: I2C 0x18
 100     Datasheet: Publicly available at the Maxim website
 101                http://www.maxim-ic.com/datasheet/index.mvp/id/4199
 102   * Maxim MAX6696
 103     Prefix: 'max6695'
 104     Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
 105                            0x4c, 0x4d and 0x4e
 106     Datasheet: Publicly available at the Maxim website
 107                http://www.maxim-ic.com/datasheet/index.mvp/id/4199
 108   * Winbond/Nuvoton W83L771W/G
 109     Prefix: 'w83l771'
 110     Addresses scanned: I2C 0x4c
 111     Datasheet: No longer available
 112   * Winbond/Nuvoton W83L771AWG/ASG
 113     Prefix: 'w83l771'
 114     Addresses scanned: I2C 0x4c
 115     Datasheet: Not publicly available, can be requested from Nuvoton
 116
 117
 118 Author: Jean Delvare <khali@linux-fr.org>
 119
 120
 121 Description
 122 -----------
 123
 124 The LM90 is a digital temperature sensor. It senses its own temperature as
 125 well as the temperature of up to one external diode. It is compatible
 126 with many other devices, many of which are supported by this driver.
 127
 128 Note that there is no easy way to differentiate between the MAX6657,
 129 MAX6658 and MAX6659 variants. The extra features of the MAX6659 are only
 130 supported by this driver if the chip is located at address 0x4d or 0x4e,
 131 or if the chip type is explicitly selected as max6659.
 132 The MAX6680 and MAX6681 only differ in their pinout, therefore they obviously
 133 can't (and don't need to) be distinguished.
 134
 135 The specificity of this family of chipsets over the ADM1021/LM84
 136 family is that it features critical limits with hysteresis, and an
 137 increased resolution of the remote temperature measurement.
 138
 139 The different chipsets of the family are not strictly identical, although
 140 very similar. For reference, here comes a non-exhaustive list of specific
 141 features:
 142
 143 LM90:
 144   * Filter and alert configuration register at 0xBF.
 145   * ALERT is triggered by temperatures over critical limits.
 146
 147 LM86 and LM89:
 148   * Same as LM90
 149   * Better external channel accuracy
 150
 151 LM99:
 152   * Same as LM89
 153   * External temperature shifted by 16 degrees down
 154
 155 ADM1032:
 156   * Consecutive alert register at 0x22.
 157   * Conversion averaging.
 158   * Up to 64 conversions/s.
 159   * ALERT is triggered by open remote sensor.
 160   * SMBus PEC support for Write Byte and Receive Byte transactions.
 161
 162 ADT7461, ADT7461A, NCT1008:
 163   * Extended temperature range (breaks compatibility)
 164   * Lower resolution for remote temperature
 165
 166 MAX6657 and MAX6658:
 167   * Better local resolution
 168   * Remote sensor type selection
 169
 170 MAX6659:
 171   * Better local resolution
 172   * Selectable address
 173   * Second critical temperature limit
 174   * Remote sensor type selection
 175
 176 MAX6680 and MAX6681:
 177   * Selectable address
 178   * Remote sensor type selection
 179
 180 MAX6695 and MAX6696:
 181   * Better local resolution
 182   * Selectable address (max6696)
 183   * Second critical temperature limit
 184   * Two remote sensors
 185
 186 W83L771W/G
 187   * The G variant is lead-free, otherwise similar to the W.
 188   * Filter and alert configuration register at 0xBF
 189   * Moving average (depending on conversion rate)
 190
 191 W83L771AWG/ASG
 192   * Successor of the W83L771W/G, same features.
 193   * The AWG and ASG variants only differ in package format.
 194   * Diode ideality factor configuration (remote sensor) at 0xE3
 195
 196 All temperature values are given in degrees Celsius. Resolution
 197 is 1.0 degree for the local temperature, 0.125 degree for the remote
 198 temperature, except for the MAX6657, MAX6658 and MAX6659 which have a
 199 resolution of 0.125 degree for both temperatures.
 200
 201 Each sensor has its own high and low limits, plus a critical limit.
 202 Additionally, there is a relative hysteresis value common to both critical
 203 values. To make life easier to user-space applications, two absolute values
 204 are exported, one for each channel, but these values are of course linked.
 205 Only the local hysteresis can be set from user-space, and the same delta
 206 applies to the remote hysteresis.
 207
 208 The lm90 driver will not update its values more frequently than every
 209 other second; reading them more often will do no harm, but will return
 210 'old' values.
 211
 212 SMBus Alert Support
 213 -------------------
 214
 215 This driver has basic support for SMBus alert. When an alert is received,
 216 the status register is read and the faulty temperature channel is logged.
 217
 218 The Analog Devices chips (ADM1032, ADT7461 and ADT7461A) and ON
 219 Semiconductor chips (NCT1008) do not implement the SMBus alert protocol
 220 properly so additional care is needed: the ALERT output is disabled when
 221 an alert is received, and is re-enabled only when the alarm is gone.
 222 Otherwise the chip would block alerts from other chips in the bus as long
 223 as the alarm is active.
 224
 225 PEC Support
 226 -----------
 227
 228 The ADM1032 is the only chip of the family which supports PEC. It does
 229 not support PEC on all transactions though, so some care must be taken.
 230
 231 When reading a register value, the PEC byte is computed and sent by the
 232 ADM1032 chip. However, in the case of a combined transaction (SMBus Read
 233 Byte), the ADM1032 computes the CRC value over only the second half of
 234 the message rather than its entirety, because it thinks the first half
 235 of the message belongs to a different transaction. As a result, the CRC
 236 value differs from what the SMBus master expects, and all reads fail.
 237
 238 For this reason, the lm90 driver will enable PEC for the ADM1032 only if
 239 the bus supports the SMBus Send Byte and Receive Byte transaction types.
 240 These transactions will be used to read register values, instead of
 241 SMBus Read Byte, and PEC will work properly.
 242
 243 Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
 244 Instead, it will try to write the PEC value to the register (because the
 245 SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
 246 without PEC), which is not what we want. Thus, PEC is explicitly disabled
 247 on SMBus Send Byte transactions in the lm90 driver.
 248
 249 PEC on byte data transactions represents a significant increase in bandwidth
 250 usage (+33% for writes, +25% for reads) in normal conditions. With the need
 251 to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
 252 two transactions will typically mean twice as much delay waiting for
 253 transaction completion, effectively doubling the register cache refresh time.
 254 I guess reliability comes at a price, but it's quite expensive this time.
 255
 256 So, as not everyone might enjoy the slowdown, PEC can be disabled through
 257 sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
 258 to that file to enable PEC again.