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   * Texas Instruments TMP451
 126     Prefix: 'tmp451'
 127     Addresses scanned: I2C 0x4c
 128     Datasheet: Publicly available at TI website
 129                http://www.ti.com/litv/pdf/sbos686
 130
 131
 132 Author: Jean Delvare <jdelvare@suse.de>
 133
 134
 135 Description
 136 -----------
 137
 138 The LM90 is a digital temperature sensor. It senses its own temperature as
 139 well as the temperature of up to one external diode. It is compatible
 140 with many other devices, many of which are supported by this driver.
 141
 142 Note that there is no easy way to differentiate between the MAX6657,
 143 MAX6658 and MAX6659 variants. The extra features of the MAX6659 are only
 144 supported by this driver if the chip is located at address 0x4d or 0x4e,
 145 or if the chip type is explicitly selected as max6659.
 146 The MAX6680 and MAX6681 only differ in their pinout, therefore they obviously
 147 can't (and don't need to) be distinguished.
 148
 149 The specificity of this family of chipsets over the ADM1021/LM84
 150 family is that it features critical limits with hysteresis, and an
 151 increased resolution of the remote temperature measurement.
 152
 153 The different chipsets of the family are not strictly identical, although
 154 very similar. For reference, here comes a non-exhaustive list of specific
 155 features:
 156
 157 LM90:
 158   * Filter and alert configuration register at 0xBF.
 159   * ALERT is triggered by temperatures over critical limits.
 160
 161 LM86 and LM89:
 162   * Same as LM90
 163   * Better external channel accuracy
 164
 165 LM99:
 166   * Same as LM89
 167   * External temperature shifted by 16 degrees down
 168
 169 ADM1032:
 170   * Consecutive alert register at 0x22.
 171   * Conversion averaging.
 172   * Up to 64 conversions/s.
 173   * ALERT is triggered by open remote sensor.
 174   * SMBus PEC support for Write Byte and Receive Byte transactions.
 175
 176 ADT7461, ADT7461A, NCT1008:
 177   * Extended temperature range (breaks compatibility)
 178   * Lower resolution for remote temperature
 179
 180 MAX6657 and MAX6658:
 181   * Better local resolution
 182   * Remote sensor type selection
 183
 184 MAX6659:
 185   * Better local resolution
 186   * Selectable address
 187   * Second critical temperature limit
 188   * Remote sensor type selection
 189
 190 MAX6680 and MAX6681:
 191   * Selectable address
 192   * Remote sensor type selection
 193
 194 MAX6695 and MAX6696:
 195   * Better local resolution
 196   * Selectable address (max6696)
 197   * Second critical temperature limit
 198   * Two remote sensors
 199
 200 W83L771W/G
 201   * The G variant is lead-free, otherwise similar to the W.
 202   * Filter and alert configuration register at 0xBF
 203   * Moving average (depending on conversion rate)
 204
 205 W83L771AWG/ASG
 206   * Successor of the W83L771W/G, same features.
 207   * The AWG and ASG variants only differ in package format.
 208   * Diode ideality factor configuration (remote sensor) at 0xE3
 209
 210 SA56004X:
 211   * Better local resolution
 212
 213 All temperature values are given in degrees Celsius. Resolution
 214 is 1.0 degree for the local temperature, 0.125 degree for the remote
 215 temperature, except for the MAX6657, MAX6658 and MAX6659 which have a
 216 resolution of 0.125 degree for both temperatures.
 217
 218 Each sensor has its own high and low limits, plus a critical limit.
 219 Additionally, there is a relative hysteresis value common to both critical
 220 values. To make life easier to user-space applications, two absolute values
 221 are exported, one for each channel, but these values are of course linked.
 222 Only the local hysteresis can be set from user-space, and the same delta
 223 applies to the remote hysteresis.
 224
 225 The lm90 driver will not update its values more frequently than configured with
 226 the update_interval attribute; reading them more often will do no harm, but will
 227 return 'old' values.
 228
 229 SMBus Alert Support
 230 -------------------
 231
 232 This driver has basic support for SMBus alert. When an alert is received,
 233 the status register is read and the faulty temperature channel is logged.
 234
 235 The Analog Devices chips (ADM1032, ADT7461 and ADT7461A) and ON
 236 Semiconductor chips (NCT1008) do not implement the SMBus alert protocol
 237 properly so additional care is needed: the ALERT output is disabled when
 238 an alert is received, and is re-enabled only when the alarm is gone.
 239 Otherwise the chip would block alerts from other chips in the bus as long
 240 as the alarm is active.
 241
 242 PEC Support
 243 -----------
 244
 245 The ADM1032 is the only chip of the family which supports PEC. It does
 246 not support PEC on all transactions though, so some care must be taken.
 247
 248 When reading a register value, the PEC byte is computed and sent by the
 249 ADM1032 chip. However, in the case of a combined transaction (SMBus Read
 250 Byte), the ADM1032 computes the CRC value over only the second half of
 251 the message rather than its entirety, because it thinks the first half
 252 of the message belongs to a different transaction. As a result, the CRC
 253 value differs from what the SMBus master expects, and all reads fail.
 254
 255 For this reason, the lm90 driver will enable PEC for the ADM1032 only if
 256 the bus supports the SMBus Send Byte and Receive Byte transaction types.
 257 These transactions will be used to read register values, instead of
 258 SMBus Read Byte, and PEC will work properly.
 259
 260 Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
 261 Instead, it will try to write the PEC value to the register (because the
 262 SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
 263 without PEC), which is not what we want. Thus, PEC is explicitly disabled
 264 on SMBus Send Byte transactions in the lm90 driver.
 265
 266 PEC on byte data transactions represents a significant increase in bandwidth
 267 usage (+33% for writes, +25% for reads) in normal conditions. With the need
 268 to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
 269 two transactions will typically mean twice as much delay waiting for
 270 transaction completion, effectively doubling the register cache refresh time.
 271 I guess reliability comes at a price, but it's quite expensive this time.
 272
 273 So, as not everyone might enjoy the slowdown, PEC can be disabled through
 274 sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
 275 to that file to enable PEC again.