1Kernel driver via686a
2=====================
3
4Supported chips:
5
6  * Via VT82C686A, VT82C686B  Southbridge Integrated Hardware Monitor
7
8    Prefix: 'via686a'
9
10    Addresses scanned: ISA in PCI-space encoded address
11
12    Datasheet: On request through web form (http://www.via.com.tw/en/resources/download-center/)
13
14Authors:
15	- Kyösti Mälkki <kmalkki@cc.hut.fi>,
16	- Mark D. Studebaker <mdsxyz123@yahoo.com>
17	- Bob Dougherty <bobd@stanford.edu>
18	- (Some conversion-factor data were contributed by
19	- Jonathan Teh Soon Yew <j.teh@iname.com>
20	- and Alex van Kaam <darkside@chello.nl>.)
21
22Module Parameters
23-----------------
24
25======================= =======================================================
26force_addr=0xaddr       Set the I/O base address. Useful for boards that
27			don't set the address in the BIOS. Look for a BIOS
28			upgrade before resorting to this. Does not do a
29			PCI force; the via686a must still be present in lspci.
30			Don't use this unless the driver complains that the
31			base address is not set.
32			Example: 'modprobe via686a force_addr=0x6000'
33======================= =======================================================
34
35Description
36-----------
37
38The driver does not distinguish between the chips and reports
39all as a 686A.
40
41The Via 686a southbridge has integrated hardware monitor functionality.
42It also has an I2C bus, but this driver only supports the hardware monitor.
43For the I2C bus driver, see <file:Documentation/i2c/busses/i2c-viapro.rst>
44
45The Via 686a implements three temperature sensors, two fan rotation speed
46sensors, five voltage sensors and alarms.
47
48Temperatures are measured in degrees Celsius. An alarm is triggered once
49when the Overtemperature Shutdown limit is crossed; it is triggered again
50as soon as it drops below the hysteresis value.
51
52Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
53triggered if the rotation speed has dropped below a programmable limit. Fan
54readings can be divided by a programmable divider (1, 2, 4 or 8) to give
55the readings more range or accuracy. Not all RPM values can accurately be
56represented, so some rounding is done. With a divider of 2, the lowest
57representable value is around 2600 RPM.
58
59Voltage sensors (also known as IN sensors) report their values in volts.
60An alarm is triggered if the voltage has crossed a programmable minimum
61or maximum limit. Voltages are internally scalled, so each voltage channel
62has a different resolution and range.
63
64If an alarm triggers, it will remain triggered until the hardware register
65is read at least once. This means that the cause for the alarm may
66already have disappeared! Note that in the current implementation, all
67hardware registers are read whenever any data is read (unless it is less
68than 1.5 seconds since the last update). This means that you can easily
69miss once-only alarms.
70
71The driver only updates its values each 1.5 seconds; reading it more often
72will do no harm, but will return 'old' values.
73
74Known Issues
75------------
76
77This driver handles sensors integrated in some VIA south bridges. It is
78possible that a motherboard maker used a VT82C686A/B chip as part of a
79product design but was not interested in its hardware monitoring features,
80in which case the sensor inputs will not be wired. This is the case of
81the Asus K7V, A7V and A7V133 motherboards, to name only a few of them.
82So, if you need the force_addr parameter, and end up with values which
83don't seem to make any sense, don't look any further: your chip is simply
84not wired for hardware monitoring.
85