1Kernel driver adt7470 2===================== 3 4Supported chips: 5 6 * Analog Devices ADT7470 7 8 Prefix: 'adt7470' 9 10 Addresses scanned: I2C 0x2C, 0x2E, 0x2F 11 12 Datasheet: Publicly available at the Analog Devices website 13 14Author: Darrick J. Wong 15 16Description 17----------- 18 19This driver implements support for the Analog Devices ADT7470 chip. There may 20be other chips that implement this interface. 21 22The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0 23specification. Using an analog to digital converter it measures up to ten (10) 24external temperatures. It has four (4) 16-bit counters for measuring fan speed. 25There are four (4) PWM outputs that can be used to control fan speed. 26 27A sophisticated control system for the PWM outputs is designed into the ADT7470 28that allows fan speed to be adjusted automatically based on any of the ten 29temperature sensors. Each PWM output is individually adjustable and 30programmable. Once configured, the ADT7470 will adjust the PWM outputs in 31response to the measured temperatures with further host intervention. This 32feature can also be disabled for manual control of the PWM's. 33 34Each of the measured inputs (temperature, fan speed) has corresponding high/low 35limit values. The ADT7470 will signal an ALARM if any measured value exceeds 36either limit. 37 38The ADT7470 samples all inputs continuously. A kernel thread is started up for 39the purpose of periodically querying the temperature sensors, thus allowing the 40automatic fan pwm control to set the fan speed. The driver will not read the 41registers more often than once every 5 seconds. Further, configuration data is 42only read once per minute. 43 44Special Features 45---------------- 46 47The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1 48degC resolution. 49 50The Analog Devices datasheet is very detailed and describes a procedure for 51determining an optimal configuration for the automatic PWM control. 52 53Configuration Notes 54------------------- 55 56Besides standard interfaces driver adds the following: 57 58* PWM Control 59 60* pwm#_auto_point1_pwm and pwm#_auto_point1_temp and 61* pwm#_auto_point2_pwm and pwm#_auto_point2_temp - 62 63 - point1: Set the pwm speed at a lower temperature bound. 64 - point2: Set the pwm speed at a higher temperature bound. 65 66The ADT7470 will scale the pwm between the lower and higher pwm speed when 67the temperature is between the two temperature boundaries. PWM values range 68from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the 69temperature sensor associated with the PWM control exceeds 70pwm#_auto_point2_temp. 71 72The driver also allows control of the PWM frequency: 73 74* pwm1_freq 75 76The PWM frequency is rounded to the nearest one of: 77 78* 11.0 Hz 79* 14.7 Hz 80* 22.1 Hz 81* 29.4 Hz 82* 35.3 Hz 83* 44.1 Hz 84* 58.8 Hz 85* 88.2 Hz 86* 1.4 kHz 87* 22.5 kHz 88 89Notes 90----- 91 92The temperature inputs no longer need to be read periodically from userspace in 93order for the automatic pwm algorithm to run. This was the case for earlier 94versions of the driver. 95