Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 Kernel driver adt7470 2 ===================== 3 4 Supported chips: 5 * Analog Devices ADT7470 6 Prefix: 'adt7470' 7 Addresses scanned: I2C 0x2C, 0x2E, 0x2F 8 Datasheet: Publicly available at the Analog Devices website 9 10 Author: Darrick J. Wong 11 12 Description 13 ----------- 14 15 This driver implements support for the Analog Devices ADT7470 chip. There may 16 be other chips that implement this interface. 17 18 The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0 19 specification. Using an analog to digital converter it measures up to ten (10) 20 external temperatures. It has four (4) 16-bit counters for measuring fan speed. 21 There are four (4) PWM outputs that can be used to control fan speed. 22 23 A sophisticated control system for the PWM outputs is designed into the ADT7470 24 that allows fan speed to be adjusted automatically based on any of the ten 25 temperature sensors. Each PWM output is individually adjustable and 26 programmable. Once configured, the ADT7470 will adjust the PWM outputs in 27 response to the measured temperatures with further host intervention. This 28 feature can also be disabled for manual control of the PWM's. 29 30 Each of the measured inputs (temperature, fan speed) has corresponding high/low 31 limit values. The ADT7470 will signal an ALARM if any measured value exceeds 32 either limit. 33 34 The ADT7470 samples all inputs continuously. A kernel thread is started up for 35 the purpose of periodically querying the temperature sensors, thus allowing the 36 automatic fan pwm control to set the fan speed. The driver will not read the 37 registers more often than once every 5 seconds. Further, configuration data is 38 only read once per minute. 39 40 Special Features 41 ---------------- 42 43 The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1 44 degC resolution. 45 46 The Analog Devices datasheet is very detailed and describes a procedure for 47 determining an optimal configuration for the automatic PWM control. 48 49 Configuration Notes 50 ------------------- 51 52 Besides standard interfaces driver adds the following: 53 54 * PWM Control 55 56 * pwm#_auto_point1_pwm and pwm#_auto_point1_temp and 57 * pwm#_auto_point2_pwm and pwm#_auto_point2_temp - 58 59 point1: Set the pwm speed at a lower temperature bound. 60 point2: Set the pwm speed at a higher temperature bound. 61 62 The ADT7470 will scale the pwm between the lower and higher pwm speed when 63 the temperature is between the two temperature boundaries. PWM values range 64 from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the 65 temperature sensor associated with the PWM control exceeds 66 pwm#_auto_point2_temp. 67 68 The driver also allows control of the PWM frequency: 69 70 * pwm1_freq 71 72 The PWM frequency is rounded to the nearest one of: 73 74 * 11.0 Hz 75 * 14.7 Hz 76 * 22.1 Hz 77 * 29.4 Hz 78 * 35.3 Hz 79 * 44.1 Hz 80 * 58.8 Hz 81 * 88.2 Hz 82 * 1.4 kHz 83 * 22.5 kHz 84 85 Notes 86 ----- 87 88 The temperature inputs no longer need to be read periodically from userspace in 89 order for the automatic pwm algorithm to run. This was the case for earlier 90 versions of the driver.