lm78 3.7 KB

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  1. Kernel driver lm78
  2. ==================
  3. Supported chips:
  4. * National Semiconductor LM78 / LM78-J
  5. Prefix: 'lm78'
  6. Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)
  7. Datasheet: Publicly available at the National Semiconductor website
  8. http://www.national.com/
  9. * National Semiconductor LM79
  10. Prefix: 'lm79'
  11. Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)
  12. Datasheet: Publicly available at the National Semiconductor website
  13. http://www.national.com/
  14. Author: Frodo Looijaard <frodol@dds.nl>
  15. Description
  16. -----------
  17. This driver implements support for the National Semiconductor LM78, LM78-J
  18. and LM79. They are described as 'Microprocessor System Hardware Monitors'.
  19. There is almost no difference between the three supported chips. Functionally,
  20. the LM78 and LM78-J are exactly identical. The LM79 has one more VID line,
  21. which is used to report the lower voltages newer Pentium processors use.
  22. From here on, LM7* means either of these three types.
  23. The LM7* implements one temperature sensor, three fan rotation speed sensors,
  24. seven voltage sensors, VID lines, alarms, and some miscellaneous stuff.
  25. Temperatures are measured in degrees Celsius. An alarm is triggered once
  26. when the Overtemperature Shutdown limit is crossed; it is triggered again
  27. as soon as it drops below the Hysteresis value. A more useful behavior
  28. can be found by setting the Hysteresis value to +127 degrees Celsius; in
  29. this case, alarms are issued during all the time when the actual temperature
  30. is above the Overtemperature Shutdown value. Measurements are guaranteed
  31. between -55 and +125 degrees, with a resolution of 1 degree.
  32. Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
  33. triggered if the rotation speed has dropped below a programmable limit. Fan
  34. readings can be divided by a programmable divider (1, 2, 4 or 8) to give
  35. the readings more range or accuracy. Not all RPM values can accurately be
  36. represented, so some rounding is done. With a divider of 2, the lowest
  37. representable value is around 2600 RPM.
  38. Voltage sensors (also known as IN sensors) report their values in volts.
  39. An alarm is triggered if the voltage has crossed a programmable minimum
  40. or maximum limit. Note that minimum in this case always means 'closest to
  41. zero'; this is important for negative voltage measurements. All voltage
  42. inputs can measure voltages between 0 and 4.08 volts, with a resolution
  43. of 0.016 volt.
  44. The VID lines encode the core voltage value: the voltage level your processor
  45. should work with. This is hardcoded by the mainboard and/or processor itself.
  46. It is a value in volts. When it is unconnected, you will often find the
  47. value 3.50 V here.
  48. In addition to the alarms described above, there are a couple of additional
  49. ones. There is a BTI alarm, which gets triggered when an external chip has
  50. crossed its limits. Usually, this is connected to all LM75 chips; if at
  51. least one crosses its limits, this bit gets set. The CHAS alarm triggers
  52. if your computer case is open. The FIFO alarms should never trigger; it
  53. indicates an internal error. The SMI_IN alarm indicates some other chip
  54. has triggered an SMI interrupt. As we do not use SMI interrupts at all,
  55. this condition usually indicates there is a problem with some other
  56. device.
  57. If an alarm triggers, it will remain triggered until the hardware register
  58. is read at least once. This means that the cause for the alarm may
  59. already have disappeared! Note that in the current implementation, all
  60. hardware registers are read whenever any data is read (unless it is less
  61. than 1.5 seconds since the last update). This means that you can easily
  62. miss once-only alarms.
  63. The LM7* only updates its values each 1.5 seconds; reading it more often
  64. will do no harm, but will return 'old' values.