lm90 8.7 KB

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  1. Kernel driver lm90
  2. ==================
  3. Supported chips:
  4. * National Semiconductor LM90
  5. Prefix: 'lm90'
  6. Addresses scanned: I2C 0x4c
  7. Datasheet: Publicly available at the National Semiconductor website
  8. http://www.national.com/pf/LM/LM90.html
  9. * National Semiconductor LM89
  10. Prefix: 'lm89' (no auto-detection)
  11. Addresses scanned: I2C 0x4c and 0x4d
  12. Datasheet: Publicly available at the National Semiconductor website
  13. http://www.national.com/mpf/LM/LM89.html
  14. * National Semiconductor LM99
  15. Prefix: 'lm99'
  16. Addresses scanned: I2C 0x4c and 0x4d
  17. Datasheet: Publicly available at the National Semiconductor website
  18. http://www.national.com/pf/LM/LM99.html
  19. * National Semiconductor LM86
  20. Prefix: 'lm86'
  21. Addresses scanned: I2C 0x4c
  22. Datasheet: Publicly available at the National Semiconductor website
  23. http://www.national.com/mpf/LM/LM86.html
  24. * Analog Devices ADM1032
  25. Prefix: 'adm1032'
  26. Addresses scanned: I2C 0x4c and 0x4d
  27. Datasheet: Publicly available at the ON Semiconductor website
  28. http://www.onsemi.com/PowerSolutions/product.do?id=ADM1032
  29. * Analog Devices ADT7461
  30. Prefix: 'adt7461'
  31. Addresses scanned: I2C 0x4c and 0x4d
  32. Datasheet: Publicly available at the ON Semiconductor website
  33. http://www.onsemi.com/PowerSolutions/product.do?id=ADT7461
  34. * Maxim MAX6646
  35. Prefix: 'max6646'
  36. Addresses scanned: I2C 0x4d
  37. Datasheet: Publicly available at the Maxim website
  38. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
  39. * Maxim MAX6647
  40. Prefix: 'max6646'
  41. Addresses scanned: I2C 0x4e
  42. Datasheet: Publicly available at the Maxim website
  43. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
  44. * Maxim MAX6648
  45. Prefix: 'max6646'
  46. Addresses scanned: I2C 0x4c
  47. Datasheet: Publicly available at the Maxim website
  48. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500
  49. * Maxim MAX6649
  50. Prefix: 'max6646'
  51. Addresses scanned: I2C 0x4c
  52. Datasheet: Publicly available at the Maxim website
  53. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
  54. * Maxim MAX6657
  55. Prefix: 'max6657'
  56. Addresses scanned: I2C 0x4c
  57. Datasheet: Publicly available at the Maxim website
  58. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
  59. * Maxim MAX6658
  60. Prefix: 'max6657'
  61. Addresses scanned: I2C 0x4c
  62. Datasheet: Publicly available at the Maxim website
  63. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
  64. * Maxim MAX6659
  65. Prefix: 'max6657'
  66. Addresses scanned: I2C 0x4c, 0x4d (unsupported 0x4e)
  67. Datasheet: Publicly available at the Maxim website
  68. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
  69. * Maxim MAX6680
  70. Prefix: 'max6680'
  71. Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
  72. 0x4c, 0x4d and 0x4e
  73. Datasheet: Publicly available at the Maxim website
  74. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
  75. * Maxim MAX6681
  76. Prefix: 'max6680'
  77. Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
  78. 0x4c, 0x4d and 0x4e
  79. Datasheet: Publicly available at the Maxim website
  80. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
  81. * Maxim MAX6692
  82. Prefix: 'max6646'
  83. Addresses scanned: I2C 0x4c
  84. Datasheet: Publicly available at the Maxim website
  85. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500
  86. * Winbond/Nuvoton W83L771AWG/ASG
  87. Prefix: 'w83l771'
  88. Addresses scanned: I2C 0x4c
  89. Datasheet: Not publicly available, can be requested from Nuvoton
  90. Author: Jean Delvare <khali@linux-fr.org>
  91. Description
  92. -----------
  93. The LM90 is a digital temperature sensor. It senses its own temperature as
  94. well as the temperature of up to one external diode. It is compatible
  95. with many other devices, many of which are supported by this driver.
  96. Note that there is no easy way to differentiate between the MAX6657,
  97. MAX6658 and MAX6659 variants. The extra address and features of the
  98. MAX6659 are not supported by this driver. The MAX6680 and MAX6681 only
  99. differ in their pinout, therefore they obviously can't (and don't need to)
  100. be distinguished.
  101. The specificity of this family of chipsets over the ADM1021/LM84
  102. family is that it features critical limits with hysteresis, and an
  103. increased resolution of the remote temperature measurement.
  104. The different chipsets of the family are not strictly identical, although
  105. very similar. For reference, here comes a non-exhaustive list of specific
  106. features:
  107. LM90:
  108. * Filter and alert configuration register at 0xBF.
  109. * ALERT is triggered by temperatures over critical limits.
  110. LM86 and LM89:
  111. * Same as LM90
  112. * Better external channel accuracy
  113. LM99:
  114. * Same as LM89
  115. * External temperature shifted by 16 degrees down
  116. ADM1032:
  117. * Consecutive alert register at 0x22.
  118. * Conversion averaging.
  119. * Up to 64 conversions/s.
  120. * ALERT is triggered by open remote sensor.
  121. * SMBus PEC support for Write Byte and Receive Byte transactions.
  122. ADT7461:
  123. * Extended temperature range (breaks compatibility)
  124. * Lower resolution for remote temperature
  125. MAX6657 and MAX6658:
  126. * Better local resolution
  127. * Remote sensor type selection
  128. MAX6659:
  129. * Better local resolution
  130. * Selectable address
  131. * Second critical temperature limit
  132. * Remote sensor type selection
  133. MAX6680 and MAX6681:
  134. * Selectable address
  135. * Remote sensor type selection
  136. W83L771AWG/ASG
  137. * The AWG and ASG variants only differ in package format.
  138. * Filter and alert configuration register at 0xBF
  139. * Diode ideality factor configuration (remote sensor) at 0xE3
  140. * Moving average (depending on conversion rate)
  141. All temperature values are given in degrees Celsius. Resolution
  142. is 1.0 degree for the local temperature, 0.125 degree for the remote
  143. temperature, except for the MAX6657, MAX6658 and MAX6659 which have a
  144. resolution of 0.125 degree for both temperatures.
  145. Each sensor has its own high and low limits, plus a critical limit.
  146. Additionally, there is a relative hysteresis value common to both critical
  147. values. To make life easier to user-space applications, two absolute values
  148. are exported, one for each channel, but these values are of course linked.
  149. Only the local hysteresis can be set from user-space, and the same delta
  150. applies to the remote hysteresis.
  151. The lm90 driver will not update its values more frequently than every
  152. other second; reading them more often will do no harm, but will return
  153. 'old' values.
  154. SMBus Alert Support
  155. -------------------
  156. This driver has basic support for SMBus alert. When an alert is received,
  157. the status register is read and the faulty temperature channel is logged.
  158. The Analog Devices chips (ADM1032 and ADT7461) do not implement the SMBus
  159. alert protocol properly so additional care is needed: the ALERT output is
  160. disabled when an alert is received, and is re-enabled only when the alarm
  161. is gone. Otherwise the chip would block alerts from other chips in the bus
  162. as long as the alarm is active.
  163. PEC Support
  164. -----------
  165. The ADM1032 is the only chip of the family which supports PEC. It does
  166. not support PEC on all transactions though, so some care must be taken.
  167. When reading a register value, the PEC byte is computed and sent by the
  168. ADM1032 chip. However, in the case of a combined transaction (SMBus Read
  169. Byte), the ADM1032 computes the CRC value over only the second half of
  170. the message rather than its entirety, because it thinks the first half
  171. of the message belongs to a different transaction. As a result, the CRC
  172. value differs from what the SMBus master expects, and all reads fail.
  173. For this reason, the lm90 driver will enable PEC for the ADM1032 only if
  174. the bus supports the SMBus Send Byte and Receive Byte transaction types.
  175. These transactions will be used to read register values, instead of
  176. SMBus Read Byte, and PEC will work properly.
  177. Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
  178. Instead, it will try to write the PEC value to the register (because the
  179. SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
  180. without PEC), which is not what we want. Thus, PEC is explicitly disabled
  181. on SMBus Send Byte transactions in the lm90 driver.
  182. PEC on byte data transactions represents a significant increase in bandwidth
  183. usage (+33% for writes, +25% for reads) in normal conditions. With the need
  184. to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
  185. two transactions will typically mean twice as much delay waiting for
  186. transaction completion, effectively doubling the register cache refresh time.
  187. I guess reliability comes at a price, but it's quite expensive this time.
  188. So, as not everyone might enjoy the slowdown, PEC can be disabled through
  189. sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
  190. to that file to enable PEC again.