| Darrick J. Wong | 57df46d | 2008-02-18 13:33:23 -0800 | [diff] [blame] | 1 | Kernel driver adt7473 |
| 2 | ====================== |
| 3 | |
| 4 | Supported chips: |
| 5 | * Analog Devices ADT7473 |
| 6 | Prefix: 'adt7473' |
| 7 | Addresses scanned: I2C 0x2C, 0x2D, 0x2E |
| 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 ADT7473 chip family. |
| 16 | |
| 17 | The LM85 uses the 2-wire interface compatible with the SMBUS 2.0 |
| 18 | specification. Using an analog to digital converter it measures three (3) |
| 19 | temperatures and two (2) voltages. It has three (3) 16-bit counters for |
| 20 | measuring fan speed. There are three (3) PWM outputs that can be used |
| 21 | to control fan speed. |
| 22 | |
| 23 | A sophisticated control system for the PWM outputs is designed into the |
| 24 | LM85 that allows fan speed to be adjusted automatically based on any of the |
| 25 | three temperature sensors. Each PWM output is individually adjustable and |
| 26 | programmable. Once configured, the ADT7473 will adjust the PWM outputs in |
| 27 | response to the measured temperatures without further host intervention. |
| 28 | This feature can also be disabled for manual control of the PWM's. |
| 29 | |
| 30 | Each of the measured inputs (voltage, temperature, fan speed) has |
| 31 | corresponding high/low limit values. The ADT7473 will signal an ALARM if |
| 32 | any measured value exceeds either limit. |
| 33 | |
| 34 | The ADT7473 samples all inputs continuously. The driver will not read |
| 35 | the registers more often than once every other second. Further, |
| 36 | configuration data is only read once per minute. |
| 37 | |
| 38 | Special Features |
| 39 | ---------------- |
| 40 | |
| 41 | The ADT7473 have a 10-bit ADC and can therefore measure temperatures |
| 42 | with 0.25 degC resolution. Temperature readings can be configured either |
| 43 | for twos complement format or "Offset 64" format, wherein 63 is subtracted |
| 44 | from the raw value to get the temperature value. |
| 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 | Hardware Configurations |
| 50 | ----------------------- |
| 51 | |
| 52 | The ADT7473 chips have an optional SMBALERT output that can be used to |
| 53 | signal the chipset in case a limit is exceeded or the temperature sensors |
| 54 | fail. Individual sensor interrupts can be masked so they won't trigger |
| 55 | SMBALERT. The SMBALERT output if configured replaces the PWM2 function. |
| 56 | |
| 57 | Configuration Notes |
| 58 | ------------------- |
| 59 | |
| 60 | Besides standard interfaces driver adds the following: |
| 61 | |
| 62 | * PWM Control |
| 63 | |
| 64 | * pwm#_auto_point1_pwm and pwm#_auto_point1_temp and |
| 65 | * pwm#_auto_point2_pwm and pwm#_auto_point2_temp - |
| 66 | |
| 67 | point1: Set the pwm speed at a lower temperature bound. |
| 68 | point2: Set the pwm speed at a higher temperature bound. |
| 69 | |
| 70 | The ADT7473 will scale the pwm between the lower and higher pwm speed when |
| 71 | the temperature is between the two temperature boundaries. PWM values range |
| 72 | from 0 (off) to 255 (full speed). |
| 73 | |
| 74 | Notes |
| 75 | ----- |
| 76 | |
| 77 | The NVIDIA binary driver presents an ADT7473 chip via an on-card i2c bus. |
| 78 | Unfortunately, they fail to set the i2c adapter class, so this driver may |
| 79 | fail to find the chip until the nvidia driver is patched. |