Root/Documentation/hwmon/lm85

1Kernel driver lm85
2==================
3
4Supported chips:
5  * National Semiconductor LM85 (B and C versions)
6    Prefix: 'lm85'
7    Addresses scanned: I2C 0x2c, 0x2d, 0x2e
8    Datasheet: http://www.national.com/pf/LM/LM85.html
9  * Analog Devices ADM1027
10    Prefix: 'adm1027'
11    Addresses scanned: I2C 0x2c, 0x2d, 0x2e
12    Datasheet: http://www.onsemi.com/PowerSolutions/product.do?id=ADM1027
13  * Analog Devices ADT7463
14    Prefix: 'adt7463'
15    Addresses scanned: I2C 0x2c, 0x2d, 0x2e
16    Datasheet: http://www.onsemi.com/PowerSolutions/product.do?id=ADT7463
17  * Analog Devices ADT7468
18    Prefix: 'adt7468'
19    Addresses scanned: I2C 0x2c, 0x2d, 0x2e
20    Datasheet: http://www.onsemi.com/PowerSolutions/product.do?id=ADT7468
21  * SMSC EMC6D100, SMSC EMC6D101
22    Prefix: 'emc6d100'
23    Addresses scanned: I2C 0x2c, 0x2d, 0x2e
24    Datasheet: http://www.smsc.com/media/Downloads_Public/discontinued/6d100.pdf
25  * SMSC EMC6D102
26    Prefix: 'emc6d102'
27    Addresses scanned: I2C 0x2c, 0x2d, 0x2e
28    Datasheet: http://www.smsc.com/main/catalog/emc6d102.html
29
30Authors:
31        Philip Pokorny <ppokorny@penguincomputing.com>,
32        Frodo Looijaard <frodol@dds.nl>,
33        Richard Barrington <rich_b_nz@clear.net.nz>,
34        Margit Schubert-While <margitsw@t-online.de>,
35        Justin Thiessen <jthiessen@penguincomputing.com>
36
37Description
38-----------
39
40This driver implements support for the National Semiconductor LM85 and
41compatible chips including the Analog Devices ADM1027, ADT7463, ADT7468 and
42SMSC EMC6D10x chips family.
43
44The LM85 uses the 2-wire interface compatible with the SMBUS 2.0
45specification. Using an analog to digital converter it measures three (3)
46temperatures and five (5) voltages. It has four (4) 16-bit counters for
47measuring fan speed. Five (5) digital inputs are provided for sampling the
48VID signals from the processor to the VRM. Lastly, there are three (3) PWM
49outputs that can be used to control fan speed.
50
51The voltage inputs have internal scaling resistors so that the following
52voltage can be measured without external resistors:
53
54  2.5V, 3.3V, 5V, 12V, and CPU core voltage (2.25V)
55
56The temperatures measured are one internal diode, and two remote diodes.
57Remote 1 is generally the CPU temperature. These inputs are designed to
58measure a thermal diode like the one in a Pentium 4 processor in a socket
59423 or socket 478 package. They can also measure temperature using a
60transistor like the 2N3904.
61
62A sophisticated control system for the PWM outputs is designed into the
63LM85 that allows fan speed to be adjusted automatically based on any of the
64three temperature sensors. Each PWM output is individually adjustable and
65programmable. Once configured, the LM85 will adjust the PWM outputs in
66response to the measured temperatures without further host intervention.
67This feature can also be disabled for manual control of the PWM's.
68
69Each of the measured inputs (voltage, temperature, fan speed) has
70corresponding high/low limit values. The LM85 will signal an ALARM if any
71measured value exceeds either limit.
72
73The LM85 samples all inputs continuously. The lm85 driver will not read
74the registers more often than once a second. Further, configuration data is
75only read once each 5 minutes. There is twice as much config data as
76measurements, so this would seem to be a worthwhile optimization.
77
78Special Features
79----------------
80
81The LM85 has four fan speed monitoring modes. The ADM1027 has only two.
82Both have special circuitry to compensate for PWM interactions with the
83TACH signal from the fans. The ADM1027 can be configured to measure the
84speed of a two wire fan, but the input conditioning circuitry is different
85for 3-wire and 2-wire mode. For this reason, the 2-wire fan modes are not
86exposed to user control. The BIOS should initialize them to the correct
87mode. If you've designed your own ADM1027, you'll have to modify the
88init_client function and add an insmod parameter to set this up.
89
90To smooth the response of fans to changes in temperature, the LM85 has an
91optional filter for smoothing temperatures. The ADM1027 has the same
92config option but uses it to rate limit the changes to fan speed instead.
93
94The ADM1027, ADT7463 and ADT7468 have a 10-bit ADC and can therefore
95measure temperatures with 0.25 degC resolution. They also provide an offset
96to the temperature readings that is automatically applied during
97measurement. This offset can be used to zero out any errors due to traces
98and placement. The documentation says that the offset is in 0.25 degC
99steps, but in initial testing of the ADM1027 it was 1.00 degC steps. Analog
100Devices has confirmed this "bug". The ADT7463 is reported to work as
101described in the documentation. The current lm85 driver does not show the
102offset register.
103
104The ADT7468 has a high-frequency PWM mode, where all PWM outputs are
105driven by a 22.5 kHz clock. This is a global mode, not per-PWM output,
106which means that setting any PWM frequency above 11.3 kHz will switch
107all 3 PWM outputs to a 22.5 kHz frequency. Conversely, setting any PWM
108frequency below 11.3 kHz will switch all 3 PWM outputs to a frequency
109between 10 and 100 Hz, which can then be tuned separately.
110
111See the vendor datasheets for more information. There is application note
112from National (AN-1260) with some additional information about the LM85.
113The Analog Devices datasheet is very detailed and describes a procedure for
114determining an optimal configuration for the automatic PWM control.
115
116The SMSC EMC6D100 & EMC6D101 monitor external voltages, temperatures, and
117fan speeds. They use this monitoring capability to alert the system to out
118of limit conditions and can automatically control the speeds of multiple
119fans in a PC or embedded system. The EMC6D101, available in a 24-pin SSOP
120package, and the EMC6D100, available in a 28-pin SSOP package, are designed
121to be register compatible. The EMC6D100 offers all the features of the
122EMC6D101 plus additional voltage monitoring and system control features.
123Unfortunately it is not possible to distinguish between the package
124versions on register level so these additional voltage inputs may read
125zero. The EMC6D102 features addtional ADC bits thus extending precision
126of voltage and temperature channels.
127
128
129Hardware Configurations
130-----------------------
131
132The LM85 can be jumpered for 3 different SMBus addresses. There are
133no other hardware configuration options for the LM85.
134
135The lm85 driver detects both LM85B and LM85C revisions of the chip. See the
136datasheet for a complete description of the differences. Other than
137identifying the chip, the driver behaves no differently with regard to
138these two chips. The LM85B is recommended for new designs.
139
140The ADM1027, ADT7463 and ADT7468 chips have an optional SMBALERT output
141that can be used to signal the chipset in case a limit is exceeded or the
142temperature sensors fail. Individual sensor interrupts can be masked so
143they won't trigger SMBALERT. The SMBALERT output if configured replaces one
144of the other functions (PWM2 or IN0). This functionality is not implemented
145in current driver.
146
147The ADT7463 and ADT7468 also have an optional THERM output/input which can
148be connected to the processor PROC_HOT output. If available, the autofan
149control dynamic Tmin feature can be enabled to keep the system temperature
150within spec (just?!) with the least possible fan noise.
151
152Configuration Notes
153-------------------
154
155Besides standard interfaces driver adds following:
156
157* Temperatures and Zones
158
159Each temperature sensor is associated with a Zone. There are three
160sensors and therefore three zones (# 1, 2 and 3). Each zone has the following
161temperature configuration points:
162
163* temp#_auto_temp_off - temperature below which fans should be off or spinning very low.
164* temp#_auto_temp_min - temperature over which fans start to spin.
165* temp#_auto_temp_max - temperature when fans spin at full speed.
166* temp#_auto_temp_crit - temperature when all fans will run full speed.
167
168* PWM Control
169
170There are three PWM outputs. The LM85 datasheet suggests that the
171pwm3 output control both fan3 and fan4. Each PWM can be individually
172configured and assigned to a zone for its control value. Each PWM can be
173configured individually according to the following options.
174
175* pwm#_auto_pwm_min - this specifies the PWM value for temp#_auto_temp_off
176                      temperature. (PWM value from 0 to 255)
177
178* pwm#_auto_pwm_minctl - this flags selects for temp#_auto_temp_off temperature
179                         the behaviour of fans. Write 1 to let fans spinning at
180             pwm#_auto_pwm_min or write 0 to let them off.
181
182NOTE: It has been reported that there is a bug in the LM85 that causes the flag
183to be associated with the zones not the PWMs. This contradicts all the
184published documentation. Setting pwm#_min_ctl in this case actually affects all
185PWMs controlled by zone '#'.
186
187* PWM Controlling Zone selection
188
189* pwm#_auto_channels - controls zone that is associated with PWM
190
191Configuration choices:
192
193   Value Meaning
194  ------ ------------------------------------------------
195      1 Controlled by Zone 1
196      2 Controlled by Zone 2
197      3 Controlled by Zone 3
198     23 Controlled by higher temp of Zone 2 or 3
199    123 Controlled by highest temp of Zone 1, 2 or 3
200      0 PWM always 0% (off)
201     -1 PWM always 100% (full on)
202     -2 Manual control (write to 'pwm#' to set)
203
204The National LM85's have two vendor specific configuration
205features. Tach. mode and Spinup Control. For more details on these,
206see the LM85 datasheet or Application Note AN-1260. These features
207are not currently supported by the lm85 driver.
208
209The Analog Devices ADM1027 has several vendor specific enhancements.
210The number of pulses-per-rev of the fans can be set, Tach monitoring
211can be optimized for PWM operation, and an offset can be applied to
212the temperatures to compensate for systemic errors in the
213measurements. These features are not currently supported by the lm85
214driver.
215
216In addition to the ADM1027 features, the ADT7463 and ADT7468 also have
217Tmin control and THERM asserted counts. Automatic Tmin control acts to
218adjust the Tmin value to maintain the measured temperature sensor at a
219specified temperature. There isn't much documentation on this feature in
220the ADT7463 data sheet. This is not supported by current driver.
221

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