| Kernel driver adt7470 |
| ===================== |
| |
| Supported chips: |
| * Analog Devices ADT7470 |
| Prefix: 'adt7470' |
| Addresses scanned: I2C 0x2C, 0x2E, 0x2F |
| Datasheet: Publicly available at the Analog Devices website |
| |
| Author: Darrick J. Wong |
| |
| Description |
| ----------- |
| |
| This driver implements support for the Analog Devices ADT7470 chip. There may |
| be other chips that implement this interface. |
| |
| The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0 |
| specification. Using an analog to digital converter it measures up to ten (10) |
| external temperatures. It has four (4) 16-bit counters for measuring fan speed. |
| There are four (4) PWM outputs that can be used to control fan speed. |
| |
| A sophisticated control system for the PWM outputs is designed into the ADT7470 |
| that allows fan speed to be adjusted automatically based on any of the ten |
| temperature sensors. Each PWM output is individually adjustable and |
| programmable. Once configured, the ADT7470 will adjust the PWM outputs in |
| response to the measured temperatures with further host intervention. This |
| feature can also be disabled for manual control of the PWM's. |
| |
| Each of the measured inputs (temperature, fan speed) has corresponding high/low |
| limit values. The ADT7470 will signal an ALARM if any measured value exceeds |
| either limit. |
| |
| The ADT7470 samples all inputs continuously. A kernel thread is started up for |
| the purpose of periodically querying the temperature sensors, thus allowing the |
| automatic fan pwm control to set the fan speed. The driver will not read the |
| registers more often than once every 5 seconds. Further, configuration data is |
| only read once per minute. |
| |
| Special Features |
| ---------------- |
| |
| The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1 |
| degC resolution. |
| |
| The Analog Devices datasheet is very detailed and describes a procedure for |
| determining an optimal configuration for the automatic PWM control. |
| |
| Configuration Notes |
| ------------------- |
| |
| Besides standard interfaces driver adds the following: |
| |
| * PWM Control |
| |
| * pwm#_auto_point1_pwm and pwm#_auto_point1_temp and |
| * pwm#_auto_point2_pwm and pwm#_auto_point2_temp - |
| |
| point1: Set the pwm speed at a lower temperature bound. |
| point2: Set the pwm speed at a higher temperature bound. |
| |
| The ADT7470 will scale the pwm between the lower and higher pwm speed when |
| the temperature is between the two temperature boundaries. PWM values range |
| from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the |
| temperature sensor associated with the PWM control exceeds |
| pwm#_auto_point2_temp. |
| |
| The driver also allows control of the PWM frequency: |
| |
| * pwm1_freq |
| |
| The PWM frequency is rounded to the nearest one of: |
| |
| * 11.0 Hz |
| * 14.7 Hz |
| * 22.1 Hz |
| * 29.4 Hz |
| * 35.3 Hz |
| * 44.1 Hz |
| * 58.8 Hz |
| * 88.2 Hz |
| * 1.4 kHz |
| * 22.5 kHz |
| |
| Notes |
| ----- |
| |
| The temperature inputs no longer need to be read periodically from userspace in |
| order for the automatic pwm algorithm to run. This was the case for earlier |
| versions of the driver. |
