linux/Documentation/hwmon/lm90
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   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  * 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
 126Author: Jean Delvare <khali@linux-fr.org>
 127
 128
 129Description
 130-----------
 131
 132The LM90 is a digital temperature sensor. It senses its own temperature as
 133well as the temperature of up to one external diode. It is compatible
 134with many other devices, many of which are supported by this driver.
 135
 136Note that there is no easy way to differentiate between the MAX6657,
 137MAX6658 and MAX6659 variants. The extra features of the MAX6659 are only
 138supported by this driver if the chip is located at address 0x4d or 0x4e,
 139or if the chip type is explicitly selected as max6659.
 140The MAX6680 and MAX6681 only differ in their pinout, therefore they obviously
 141can't (and don't need to) be distinguished.
 142
 143The specificity of this family of chipsets over the ADM1021/LM84
 144family is that it features critical limits with hysteresis, and an
 145increased resolution of the remote temperature measurement.
 146
 147The different chipsets of the family are not strictly identical, although
 148very similar. For reference, here comes a non-exhaustive list of specific
 149features:
 150
 151LM90:
 152  * Filter and alert configuration register at 0xBF.
 153  * ALERT is triggered by temperatures over critical limits.
 154
 155LM86 and LM89:
 156  * Same as LM90
 157  * Better external channel accuracy
 158
 159LM99:
 160  * Same as LM89
 161  * External temperature shifted by 16 degrees down
 162
 163ADM1032:
 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
 170ADT7461, ADT7461A, NCT1008:
 171  * Extended temperature range (breaks compatibility)
 172  * Lower resolution for remote temperature
 173
 174MAX6657 and MAX6658:
 175  * Better local resolution
 176  * Remote sensor type selection
 177
 178MAX6659:
 179  * Better local resolution
 180  * Selectable address
 181  * Second critical temperature limit
 182  * Remote sensor type selection
 183
 184MAX6680 and MAX6681:
 185  * Selectable address
 186  * Remote sensor type selection
 187
 188MAX6695 and MAX6696:
 189  * Better local resolution
 190  * Selectable address (max6696)
 191  * Second critical temperature limit
 192  * Two remote sensors
 193
 194W83L771W/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
 199W83L771AWG/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
 204SA56004X:
 205  * Better local resolution
 206
 207All temperature values are given in degrees Celsius. Resolution
 208is 1.0 degree for the local temperature, 0.125 degree for the remote
 209temperature, except for the MAX6657, MAX6658 and MAX6659 which have a
 210resolution of 0.125 degree for both temperatures.
 211
 212Each sensor has its own high and low limits, plus a critical limit.
 213Additionally, there is a relative hysteresis value common to both critical
 214values. To make life easier to user-space applications, two absolute values
 215are exported, one for each channel, but these values are of course linked.
 216Only the local hysteresis can be set from user-space, and the same delta
 217applies to the remote hysteresis.
 218
 219The lm90 driver will not update its values more frequently than configured with
 220the update_interval attribute; reading them more often will do no harm, but will
 221return 'old' values.
 222
 223SMBus Alert Support
 224-------------------
 225
 226This driver has basic support for SMBus alert. When an alert is received,
 227the status register is read and the faulty temperature channel is logged.
 228
 229The Analog Devices chips (ADM1032, ADT7461 and ADT7461A) and ON
 230Semiconductor chips (NCT1008) do not implement the SMBus alert protocol
 231properly so additional care is needed: the ALERT output is disabled when
 232an alert is received, and is re-enabled only when the alarm is gone.
 233Otherwise the chip would block alerts from other chips in the bus as long
 234as the alarm is active.
 235
 236PEC Support
 237-----------
 238
 239The ADM1032 is the only chip of the family which supports PEC. It does
 240not support PEC on all transactions though, so some care must be taken.
 241
 242When reading a register value, the PEC byte is computed and sent by the
 243ADM1032 chip. However, in the case of a combined transaction (SMBus Read
 244Byte), the ADM1032 computes the CRC value over only the second half of
 245the message rather than its entirety, because it thinks the first half
 246of the message belongs to a different transaction. As a result, the CRC
 247value differs from what the SMBus master expects, and all reads fail.
 248
 249For this reason, the lm90 driver will enable PEC for the ADM1032 only if
 250the bus supports the SMBus Send Byte and Receive Byte transaction types.
 251These transactions will be used to read register values, instead of
 252SMBus Read Byte, and PEC will work properly.
 253
 254Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
 255Instead, it will try to write the PEC value to the register (because the
 256SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
 257without PEC), which is not what we want. Thus, PEC is explicitly disabled
 258on SMBus Send Byte transactions in the lm90 driver.
 259
 260PEC on byte data transactions represents a significant increase in bandwidth
 261usage (+33% for writes, +25% for reads) in normal conditions. With the need
 262to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
 263two transactions will typically mean twice as much delay waiting for
 264transaction completion, effectively doubling the register cache refresh time.
 265I guess reliability comes at a price, but it's quite expensive this time.
 266
 267So, as not everyone might enjoy the slowdown, PEC can be disabled through
 268sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
 269to that file to enable PEC again.
 270
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