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   * Philips/NXP SA56004X
 117     Prefix: 'sa56004'
 118     Addresses scanned: I2C 0x48 through 0x4F
 119     Datasheet: Publicly available at NXP website
 120                http://ics.nxp.com/products/interface/datasheet/sa56004x.pdf
 121   * GMT G781
 122     Prefix: 'g781'
 123     Addresses scanned: I2C 0x4c, 0x4d
 124     Datasheet: Not publicly available from GMT
 125
 126 Author: Jean Delvare <khali@linux-fr.org>
 127
 128
 129 Description
 130 -----------
 131
 132 The LM90 is a digital temperature sensor. It senses its own temperature as
 133 well as the temperature of up to one external diode. It is compatible
 134 with many other devices, many of which are supported by this driver.
 135
 136 Note that there is no easy way to differentiate between the MAX6657,
 137 MAX6658 and MAX6659 variants. The extra features of the MAX6659 are only
 138 supported by this driver if the chip is located at address 0x4d or 0x4e,
 139 or if the chip type is explicitly selected as max6659.
 140 The MAX6680 and MAX6681 only differ in their pinout, therefore they obviously
 141 can't (and don't need to) be distinguished.
 142
 143 The specificity of this family of chipsets over the ADM1021/LM84
 144 family is that it features critical limits with hysteresis, and an
 145 increased resolution of the remote temperature measurement.
 146
 147 The different chipsets of the family are not strictly identical, although
 148 very similar. For reference, here comes a non-exhaustive list of specific
 149 features:
 150
 151 LM90:
 152   * Filter and alert configuration register at 0xBF.
 153   * ALERT is triggered by temperatures over critical limits.
 154
 155 LM86 and LM89:
 156   * Same as LM90
 157   * Better external channel accuracy
 158
 159 LM99:
 160   * Same as LM89
 161   * External temperature shifted by 16 degrees down
 162
 163 ADM1032:
 164   * Consecutive alert register at 0x22.
 165   * Conversion averaging.
 166   * Up to 64 conversions/s.
 167   * ALERT is triggered by open remote sensor.
 168   * SMBus PEC support for Write Byte and Receive Byte transactions.
 169
 170 ADT7461, ADT7461A, NCT1008:
 171   * Extended temperature range (breaks compatibility)
 172   * Lower resolution for remote temperature
 173
 174 MAX6657 and MAX6658:
 175   * Better local resolution
 176   * Remote sensor type selection
 177
 178 MAX6659:
 179   * Better local resolution
 180   * Selectable address
 181   * Second critical temperature limit
 182   * Remote sensor type selection
 183
 184 MAX6680 and MAX6681:
 185   * Selectable address
 186   * Remote sensor type selection
 187
 188 MAX6695 and MAX6696:
 189   * Better local resolution
 190   * Selectable address (max6696)
 191   * Second critical temperature limit
 192   * Two remote sensors
 193
 194 W83L771W/G
 195   * The G variant is lead-free, otherwise similar to the W.
 196   * Filter and alert configuration register at 0xBF
 197   * Moving average (depending on conversion rate)
 198
 199 W83L771AWG/ASG
 200   * Successor of the W83L771W/G, same features.
 201   * The AWG and ASG variants only differ in package format.
 202   * Diode ideality factor configuration (remote sensor) at 0xE3
 203
 204 SA56004X:
 205   * Better local resolution
 206
 207 All temperature values are given in degrees Celsius. Resolution
 208 is 1.0 degree for the local temperature, 0.125 degree for the remote
 209 temperature, except for the MAX6657, MAX6658 and MAX6659 which have a
 210 resolution of 0.125 degree for both temperatures.
 211
 212 Each sensor has its own high and low limits, plus a critical limit.
 213 Additionally, there is a relative hysteresis value common to both critical
 214 values. To make life easier to user-space applications, two absolute values
 215 are exported, one for each channel, but these values are of course linked.
 216 Only the local hysteresis can be set from user-space, and the same delta
 217 applies to the remote hysteresis.
 218
 219 The lm90 driver will not update its values more frequently than configured with
 220 the update_interval attribute; reading them more often will do no harm, but will
 221 return 'old' values.
 222
 223 SMBus Alert Support
 224 -------------------
 225
 226 This driver has basic support for SMBus alert. When an alert is received,
 227 the status register is read and the faulty temperature channel is logged.
 228
 229 The Analog Devices chips (ADM1032, ADT7461 and ADT7461A) and ON
 230 Semiconductor chips (NCT1008) do not implement the SMBus alert protocol
 231 properly so additional care is needed: the ALERT output is disabled when
 232 an alert is received, and is re-enabled only when the alarm is gone.
 233 Otherwise the chip would block alerts from other chips in the bus as long
 234 as the alarm is active.
 235
 236 PEC Support
 237 -----------
 238
 239 The ADM1032 is the only chip of the family which supports PEC. It does
 240 not support PEC on all transactions though, so some care must be taken.
 241
 242 When reading a register value, the PEC byte is computed and sent by the
 243 ADM1032 chip. However, in the case of a combined transaction (SMBus Read
 244 Byte), the ADM1032 computes the CRC value over only the second half of
 245 the message rather than its entirety, because it thinks the first half
 246 of the message belongs to a different transaction. As a result, the CRC
 247 value differs from what the SMBus master expects, and all reads fail.
 248
 249 For this reason, the lm90 driver will enable PEC for the ADM1032 only if
 250 the bus supports the SMBus Send Byte and Receive Byte transaction types.
 251 These transactions will be used to read register values, instead of
 252 SMBus Read Byte, and PEC will work properly.
 253
 254 Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
 255 Instead, it will try to write the PEC value to the register (because the
 256 SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
 257 without PEC), which is not what we want. Thus, PEC is explicitly disabled
 258 on SMBus Send Byte transactions in the lm90 driver.
 259
 260 PEC on byte data transactions represents a significant increase in bandwidth
 261 usage (+33% for writes, +25% for reads) in normal conditions. With the need
 262 to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
 263 two transactions will typically mean twice as much delay waiting for
 264 transaction completion, effectively doubling the register cache refresh time.
 265 I guess reliability comes at a price, but it's quite expensive this time.
 266
 267 So, as not everyone might enjoy the slowdown, PEC can be disabled through
 268 sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
 269 to that file to enable PEC again.