| Darrick J. Wong | d664a48 | 2008-10-17 17:51:20 +0200 | [diff] [blame^] | 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 DOES NOT sample all inputs continuously. A single pin on the |
| 35 | ADT7470 is connected to a multitude of thermal diodes, but the chip must be |
| 36 | instructed explicitly to read the multitude of diodes. If you want to use |
| 37 | automatic fan control mode, you must manually read any of the temperature |
| 38 | sensors or the fan control algorithm will not run. The chip WILL NOT DO THIS |
| 39 | AUTOMATICALLY; this must be done from userspace. This may be a bug in the chip |
| 40 | design, given that many other AD chips take care of this. The driver will not |
| 41 | read the registers more often than once every 5 seconds. Further, |
| 42 | configuration data is only read once per minute. |
| 43 | |
| 44 | Special Features |
| 45 | ---------------- |
| 46 | |
| 47 | The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1 |
| 48 | degC resolution. |
| 49 | |
| 50 | The Analog Devices datasheet is very detailed and describes a procedure for |
| 51 | determining an optimal configuration for the automatic PWM control. |
| 52 | |
| 53 | Configuration Notes |
| 54 | ------------------- |
| 55 | |
| 56 | Besides 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 | |
| 66 | The ADT7470 will scale the pwm between the lower and higher pwm speed when |
| 67 | the temperature is between the two temperature boundaries. PWM values range |
| 68 | from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the |
| 69 | temperature sensor associated with the PWM control exceeds |
| 70 | pwm#_auto_point2_temp. |
| 71 | |
| 72 | Notes |
| 73 | ----- |
| 74 | |
| 75 | As stated above, the temperature inputs must be read periodically from |
| 76 | userspace in order for the automatic pwm algorithm to run. |