--- /dev/null
+Kernel driver vt1211
+====================
+
+Supported chips:
+ * VIA VT1211
+ Prefix: 'vt1211'
+ Addresses scanned: none, address read from Super-I/O config space
+ Datasheet: Provided by VIA upon request and under NDA
+
+Authors: Juerg Haefliger <juergh@gmail.com>
+
+This driver is based on the driver for kernel 2.4 by Mark D. Studebaker and
+its port to kernel 2.6 by Lars Ekman.
+
+Thanks to Joseph Chan and Fiona Gatt from VIA for providing documentation and
+technical support.
+
+
+Module Parameters
+-----------------
+
+* uch_config: int Override the BIOS default universal channel (UCH)
+ configuration for channels 1-5.
+ Legal values are in the range of 0-31. Bit 0 maps to
+ UCH1, bit 1 maps to UCH2 and so on. Setting a bit to 1
+ enables the thermal input of that particular UCH and
+ setting a bit to 0 enables the voltage input.
+
+* int_mode: int Override the BIOS default temperature interrupt mode.
+ The only possible value is 0 which forces interrupt
+ mode 0. In this mode, any pending interrupt is cleared
+ when the status register is read but is regenerated as
+ long as the temperature stays above the hysteresis
+ limit.
+
+Be aware that overriding BIOS defaults might cause some unwanted side effects!
+
+
+Description
+-----------
+
+The VIA VT1211 Super-I/O chip includes complete hardware monitoring
+capabilities. It monitors 2 dedicated temperature sensor inputs (temp1 and
+temp2), 1 dedicated voltage (in5) and 2 fans. Additionally, the chip
+implements 5 universal input channels (UCH1-5) that can be individually
+programmed to either monitor a voltage or a temperature.
+
+This chip also provides manual and automatic control of fan speeds (according
+to the datasheet). The driver only supports automatic control since the manual
+mode doesn't seem to work as advertised in the datasheet. In fact I couldn't
+get manual mode to work at all! Be aware that automatic mode hasn't been
+tested very well (due to the fact that my EPIA M10000 doesn't have the fans
+connected to the PWM outputs of the VT1211 :-().
+
+The following table shows the relationship between the vt1211 inputs and the
+sysfs nodes.
+
+Sensor Voltage Mode Temp Mode Default Use (from the datasheet)
+------ ------------ --------- --------------------------------
+Reading 1 temp1 Intel thermal diode
+Reading 3 temp2 Internal thermal diode
+UCH1/Reading2 in0 temp3 NTC type thermistor
+UCH2 in1 temp4 +2.5V
+UCH3 in2 temp5 VccP (processor core)
+UCH4 in3 temp6 +5V
+UCH5 in4 temp7 +12V
++3.3V in5 Internal VCC (+3.3V)
+
+
+Voltage Monitoring
+------------------
+
+Voltages are sampled by an 8-bit ADC with a LSB of ~10mV. The supported input
+range is thus from 0 to 2.60V. Voltage values outside of this range need
+external scaling resistors. This external scaling needs to be compensated for
+via compute lines in sensors.conf, like:
+
+compute inx @*(1+R1/R2), @/(1+R1/R2)
+
+The board level scaling resistors according to VIA's recommendation are as
+follows. And this is of course totally dependent on the actual board
+implementation :-) You will have to find documentation for your own
+motherboard and edit sensors.conf accordingly.
+
+ Expected
+Voltage R1 R2 Divider Raw Value
+-----------------------------------------------
++2.5V 2K 10K 1.2 2083 mV
+VccP --- --- 1.0 1400 mV (1)
++5V 14K 10K 2.4 2083 mV
++12V 47K 10K 5.7 2105 mV
++3.3V (int) 2K 3.4K 1.588 3300 mV (2)
++3.3V (ext) 6.8K 10K 1.68 1964 mV
+
+(1) Depending on the CPU (1.4V is for a VIA C3 Nehemiah).
+(2) R1 and R2 for 3.3V (int) are internal to the VT1211 chip and the driver
+ performs the scaling and returns the properly scaled voltage value.
+
+Each measured voltage has an associated low and high limit which triggers an
+alarm when crossed.
+
+
+Temperature Monitoring
+----------------------
+
+Temperatures are reported in millidegree Celsius. Each measured temperature
+has a high limit which triggers an alarm if crossed. There is an associated
+hysteresis value with each temperature below which the temperature has to drop
+before the alarm is cleared (this is only true for interrupt mode 0). The
+interrupt mode can be forced to 0 in case the BIOS doesn't do it
+automatically. See the 'Module Parameters' section for details.
+
+All temperature channels except temp2 are external. Temp2 is the VT1211
+internal thermal diode and the driver does all the scaling for temp2 and
+returns the temperature in millidegree Celsius. For the external channels
+temp1 and temp3-temp7, scaling depends on the board implementation and needs
+to be performed in userspace via sensors.conf.
+
+Temp1 is an Intel-type thermal diode which requires the following formula to
+convert between sysfs readings and real temperatures:
+
+compute temp1 (@-Offset)/Gain, (@*Gain)+Offset
+
+According to the VIA VT1211 BIOS porting guide, the following gain and offset
+values should be used:
+
+Diode Type Offset Gain
+---------- ------ ----
+Intel CPU 88.638 0.9528
+ 65.000 0.9686 *)
+VIA C3 Ezra 83.869 0.9528
+VIA C3 Ezra-T 73.869 0.9528
+
+*) This is the formula from the lm_sensors 2.10.0 sensors.conf file. I don't
+know where it comes from or how it was derived, it's just listed here for
+completeness.
+
+Temp3-temp7 support NTC thermistors. For these channels, the driver returns
+the voltages as seen at the individual pins of UCH1-UCH5. The voltage at the
+pin (Vpin) is formed by a voltage divider made of the thermistor (Rth) and a
+scaling resistor (Rs):
+
+Vpin = 2200 * Rth / (Rs + Rth) (2200 is the ADC max limit of 2200 mV)
+
+The equation for the thermistor is as follows (google it if you want to know
+more about it):
+
+Rth = Ro * exp(B * (1 / T - 1 / To)) (To is 298.15K (25C) and Ro is the
+ nominal resistance at 25C)
+
+Mingling the above two equations and assuming Rs = Ro and B = 3435 yields the
+following formula for sensors.conf:
+
+compute tempx 1 / (1 / 298.15 - (` (2200 / @ - 1)) / 3435) - 273.15,
+ 2200 / (1 + (^ (3435 / 298.15 - 3435 / (273.15 + @))))
+
+
+Fan Speed Control
+-----------------
+
+The VT1211 provides 2 programmable PWM outputs to control the speeds of 2
+fans. Writing a 2 to any of the two pwm[1-2]_enable sysfs nodes will put the
+PWM controller in automatic mode. There is only a single controller that
+controls both PWM outputs but each PWM output can be individually enabled and
+disabled.
+
+Each PWM has 4 associated distinct output duty-cycles: full, high, low and
+off. Full and off are internally hard-wired to 255 (100%) and 0 (0%),
+respectively. High and low can be programmed via
+pwm[1-2]_auto_point[2-3]_pwm. Each PWM output can be associated with a
+different thermal input but - and here's the weird part - only one set of
+thermal thresholds exist that controls both PWMs output duty-cycles. The
+thermal thresholds are accessible via pwm[1-2]_auto_point[1-4]_temp. Note
+that even though there are 2 sets of 4 auto points each, they map to the same
+registers in the VT1211 and programming one set is sufficient (actually only
+the first set pwm1_auto_point[1-4]_temp is writable, the second set is
+read-only).
+
+PWM Auto Point PWM Output Duty-Cycle
+------------------------------------------------
+pwm[1-2]_auto_point4_pwm full speed duty-cycle (hard-wired to 255)
+pwm[1-2]_auto_point3_pwm high speed duty-cycle
+pwm[1-2]_auto_point2_pwm low speed duty-cycle
+pwm[1-2]_auto_point1_pwm off duty-cycle (hard-wired to 0)
+
+Temp Auto Point Thermal Threshold
+---------------------------------------------
+pwm[1-2]_auto_point4_temp full speed temp
+pwm[1-2]_auto_point3_temp high speed temp
+pwm[1-2]_auto_point2_temp low speed temp
+pwm[1-2]_auto_point1_temp off temp
+
+Long story short, the controller implements the following algorithm to set the
+PWM output duty-cycle based on the input temperature:
+
+Thermal Threshold Output Duty-Cycle
+ (Rising Temp) (Falling Temp)
+----------------------------------------------------------
+ full speed duty-cycle full speed duty-cycle
+full speed temp
+ high speed duty-cycle full speed duty-cycle
+high speed temp
+ low speed duty-cycle high speed duty-cycle
+low speed temp
+ off duty-cycle low speed duty-cycle
+off temp
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