1 files changed, 82 insertions, 0 deletions
diff --git a/Documentation/i2c/chips/lm78 b/Documentation/i2c/chips/lm78
new file mode 100644
index 0000000..357086e
--- /dev/null
+++ b/Documentation/i2c/chips/lm78
@@ -0,0 +1,82 @@
+Kernel driver lm78
+==================
+
+Supported chips:
+  * National Semiconductor LM78
+    Prefix: 'lm78'
+    Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)
+    Datasheet: Publicly available at the National Semiconductor website
+               http://www.national.com/
+  * National Semiconductor LM78-J
+    Prefix: 'lm78-j'
+    Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)
+    Datasheet: Publicly available at the National Semiconductor website
+               http://www.national.com/
+  * National Semiconductor LM79
+    Prefix: 'lm79'
+    Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)
+    Datasheet: Publicly available at the National Semiconductor website
+               http://www.national.com/
+
+Author: Frodo Looijaard <frodol@dds.nl>
+
+Description
+-----------
+
+This driver implements support for the National Semiconductor LM78, LM78-J
+and LM79. They are described as 'Microprocessor System Hardware Monitors'.
+
+There is almost no difference between the three supported chips. Functionally,
+the LM78 and LM78-J are exactly identical. The LM79 has one more VID line,
+which is used to report the lower voltages newer Pentium processors use.
+From here on, LM7* means either of these three types.
+
+The LM7* implements one temperature sensor, three fan rotation speed sensors,
+seven voltage sensors, VID lines, alarms, and some miscellaneous stuff.
+
+Temperatures are measured in degrees Celsius. An alarm is triggered once
+when the Overtemperature Shutdown limit is crossed; it is triggered again
+as soon as it drops below the Hysteresis value. A more useful behavior
+can be found by setting the Hysteresis value to +127 degrees Celsius; in
+this case, alarms are issued during all the time when the actual temperature
+is above the Overtemperature Shutdown value. Measurements are guaranteed
+between -55 and +125 degrees, with a resolution of 1 degree.
+
+Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
+triggered if the rotation speed has dropped below a programmable limit. Fan
+readings can be divided by a programmable divider (1, 2, 4 or 8) to give
+the readings more range or accuracy. Not all RPM values can accurately be
+represented, so some rounding is done. With a divider of 2, the lowest
+representable value is around 2600 RPM.
+
+Voltage sensors (also known as IN sensors) report their values in volts.
+An alarm is triggered if the voltage has crossed a programmable minimum
+or maximum limit. Note that minimum in this case always means 'closest to
+zero'; this is important for negative voltage measurements. All voltage
+inputs can measure voltages between 0 and 4.08 volts, with a resolution
+of 0.016 volt.
+
+The VID lines encode the core voltage value: the voltage level your processor
+should work with. This is hardcoded by the mainboard and/or processor itself.
+It is a value in volts. When it is unconnected, you will often find the
+value 3.50 V here.
+
+In addition to the alarms described above, there are a couple of additional
+ones. There is a BTI alarm, which gets triggered when an external chip has
+crossed its limits. Usually, this is connected to all LM75 chips; if at
+least one crosses its limits, this bit gets set. The CHAS alarm triggers
+if your computer case is open. The FIFO alarms should never trigger; it
+indicates an internal error. The SMI_IN alarm indicates some other chip
+has triggered an SMI interrupt. As we do not use SMI interrupts at all,
+this condition usually indicates there is a problem with some other
+device.
+
+If an alarm triggers, it will remain triggered until the hardware register
+is read at least once. This means that the cause for the alarm may
+already have disappeared! Note that in the current implementation, all
+hardware registers are read whenever any data is read (unless it is less
+than 1.5 seconds since the last update). This means that you can easily
+miss once-only alarms.
+
+The LM7* only updates its values each 1.5 seconds; reading it more often
+will do no harm, but will return 'old' values.