linux/Documentation/hwmon/via686a
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   1Kernel driver via686a
   2=====================
   3
   4Supported chips:
   5  * Via VT82C686A, VT82C686B  Southbridge Integrated Hardware Monitor
   6    Prefix: 'via686a'
   7    Addresses scanned: ISA in PCI-space encoded address
   8    Datasheet: On request through web form (http://www.via.com.tw/en/resources/download-center/)
   9
  10Authors:
  11        Kyösti Mälkki <kmalkki@cc.hut.fi>,
  12        Mark D. Studebaker <mdsxyz123@yahoo.com>
  13        Bob Dougherty <bobd@stanford.edu>
  14        (Some conversion-factor data were contributed by
  15        Jonathan Teh Soon Yew <j.teh@iname.com>
  16        and Alex van Kaam <darkside@chello.nl>.)
  17
  18Module Parameters
  19-----------------
  20
  21force_addr=0xaddr       Set the I/O base address. Useful for boards that
  22                        don't set the address in the BIOS. Look for a BIOS
  23                        upgrade before resorting to this. Does not do a
  24                        PCI force; the via686a must still be present in lspci.
  25                        Don't use this unless the driver complains that the
  26                        base address is not set.
  27                        Example: 'modprobe via686a force_addr=0x6000'
  28
  29Description
  30-----------
  31
  32The driver does not distinguish between the chips and reports
  33all as a 686A.
  34
  35The Via 686a southbridge has integrated hardware monitor functionality.
  36It also has an I2C bus, but this driver only supports the hardware monitor.
  37For the I2C bus driver, see <file:Documentation/i2c/busses/i2c-viapro>
  38
  39The Via 686a implements three temperature sensors, two fan rotation speed
  40sensors, five voltage sensors and alarms.
  41
  42Temperatures are measured in degrees Celsius. An alarm is triggered once
  43when the Overtemperature Shutdown limit is crossed; it is triggered again
  44as soon as it drops below the hysteresis value.
  45
  46Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
  47triggered if the rotation speed has dropped below a programmable limit. Fan
  48readings can be divided by a programmable divider (1, 2, 4 or 8) to give
  49the readings more range or accuracy. Not all RPM values can accurately be
  50represented, so some rounding is done. With a divider of 2, the lowest
  51representable value is around 2600 RPM.
  52
  53Voltage sensors (also known as IN sensors) report their values in volts.
  54An alarm is triggered if the voltage has crossed a programmable minimum
  55or maximum limit. Voltages are internally scalled, so each voltage channel
  56has a different resolution and range.
  57
  58If an alarm triggers, it will remain triggered until the hardware register
  59is read at least once. This means that the cause for the alarm may
  60already have disappeared! Note that in the current implementation, all
  61hardware registers are read whenever any data is read (unless it is less
  62than 1.5 seconds since the last update). This means that you can easily
  63miss once-only alarms.
  64
  65The driver only updates its values each 1.5 seconds; reading it more often
  66will do no harm, but will return 'old' values.
  67
  68Known Issues
  69------------
  70
  71This driver handles sensors integrated in some VIA south bridges. It is
  72possible that a motherboard maker used a VT82C686A/B chip as part of a
  73product design but was not interested in its hardware monitoring features,
  74in which case the sensor inputs will not be wired. This is the case of
  75the Asus K7V, A7V and A7V133 motherboards, to name only a few of them.
  76So, if you need the force_addr parameter, and end up with values which
  77don't seem to make any sense, don't look any further: your chip is simply
  78not wired for hardware monitoring.
  79
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