1 Kernel driver adm1026
2 =====================
3
4 Supported chips:
5 * Analog Devices ADM1026
6 Prefix: 'adm1026'
7 Addresses scanned: I2C 0x2c, 0x2d, 0x2e
8 Datasheet: Publicly available at the Analog Devices website
9 http://www.analog.com/en/prod/0,,766_825_ADM1026,00.html
10
11 Authors:
12 Philip Pokorny <ppokorny@penguincomputing.com> for Penguin Computing
13 Justin Thiessen <jthiessen@penguincomputing.com>
14
15 Module Parameters
16 -----------------
17
18 * gpio_input: int array (min = 1, max = 17)
19 List of GPIO pins (0-16) to program as inputs
20 * gpio_output: int array (min = 1, max = 17)
21 List of GPIO pins (0-16) to program as outputs
22 * gpio_inverted: int array (min = 1, max = 17)
23 List of GPIO pins (0-16) to program as inverted
24 * gpio_normal: int array (min = 1, max = 17)
25 List of GPIO pins (0-16) to program as normal/non-inverted
26 * gpio_fan: int array (min = 1, max = 8)
27 List of GPIO pins (0-7) to program as fan tachs
28
29
30 Description
31 -----------
32
33 This driver implements support for the Analog Devices ADM1026. Analog
34 Devices calls it a "complete thermal system management controller."
35
36 The ADM1026 implements three (3) temperature sensors, 17 voltage sensors,
37 16 general purpose digital I/O lines, eight (8) fan speed sensors (8-bit),
38 an analog output and a PWM output along with limit, alarm and mask bits for
39 all of the above. There is even 8k bytes of EEPROM memory on chip.
40
41 Temperatures are measured in degrees Celsius. There are two external
42 sensor inputs and one internal sensor. Each sensor has a high and low
43 limit. If the limit is exceeded, an interrupt (#SMBALERT) can be
44 generated. The interrupts can be masked. In addition, there are over-temp
45 limits for each sensor. If this limit is exceeded, the #THERM output will
46 be asserted. The current temperature and limits have a resolution of 1
47 degree.
48
49 Fan rotation speeds are reported in RPM (rotations per minute) but measured
50 in counts of a 22.5kHz internal clock. Each fan has a high limit which
51 corresponds to a minimum fan speed. If the limit is exceeded, an interrupt
52 can be generated. Each fan can be programmed to divide the reference clock
53 by 1, 2, 4 or 8. Not all RPM values can accurately be represented, so some
54 rounding is done. With a divider of 8, the slowest measurable speed of a
55 two pulse per revolution fan is 661 RPM.
56
57 There are 17 voltage sensors. An alarm is triggered if the voltage has
58 crossed a programmable minimum or maximum limit. Note that minimum in this
59 case always means 'closest to zero'; this is important for negative voltage
60 measurements. Several inputs have integrated attenuators so they can measure
61 higher voltages directly. 3.3V, 5V, 12V, -12V and battery voltage all have
62 dedicated inputs. There are several inputs scaled to 0-3V full-scale range
63 for SCSI terminator power. The remaining inputs are not scaled and have
64 a 0-2.5V full-scale range. A 2.5V or 1.82V reference voltage is provided
65 for negative voltage measurements.
66
67 If an alarm triggers, it will remain triggered until the hardware register
68 is read at least once. This means that the cause for the alarm may already
69 have disappeared! Note that in the current implementation, all hardware
70 registers are read whenever any data is read (unless it is less than 2.0
71 seconds since the last update). This means that you can easily miss
72 once-only alarms.
73
74 The ADM1026 measures continuously. Analog inputs are measured about 4
75 times a second. Fan speed measurement time depends on fan speed and
76 divisor. It can take as long as 1.5 seconds to measure all fan speeds.
77
78 The ADM1026 has the ability to automatically control fan speed based on the
79 temperature sensor inputs. Both the PWM output and the DAC output can be
80 used to control fan speed. Usually only one of these two outputs will be
81 used. Write the minimum PWM or DAC value to the appropriate control
82 register. Then set the low temperature limit in the tmin values for each
83 temperature sensor. The range of control is fixed at 20 °C, and the
84 largest difference between current and tmin of the temperature sensors sets
85 the control output. See the datasheet for several example circuits for
86 controlling fan speed with the PWM and DAC outputs. The fan speed sensors
87 do not have PWM compensation, so it is probably best to control the fan
88 voltage from the power lead rather than on the ground lead.
89
90 The datasheet shows an example application with VID signals attached to
91 GPIO lines. Unfortunately, the chip may not be connected to the VID lines
92 in this way. The driver assumes that the chips *is* connected this way to
93 get a VID voltage.
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