| Kernel driver lm63 |
| ================== |
| |
| Supported chips: |
| * National Semiconductor LM63 |
| Prefix: 'lm63' |
| Addresses scanned: I2C 0x4c |
| Datasheet: Publicly available at the National Semiconductor website |
| http://www.national.com/pf/LM/LM63.html |
| |
| Author: Jean Delvare <khali@linux-fr.org> |
| |
| Thanks go to Tyan and especially Alex Buckingham for setting up a remote |
| access to their S4882 test platform for this driver. |
| http://www.tyan.com/ |
| |
| Description |
| ----------- |
| |
| The LM63 is a digital temperature sensor with integrated fan monitoring |
| and control. |
| |
| The LM63 is basically an LM86 with fan speed monitoring and control |
| capabilities added. It misses some of the LM86 features though: |
| - No low limit for local temperature. |
| - No critical limit for local temperature. |
| - Critical limit for remote temperature can be changed only once. We |
| will consider that the critical limit is read-only. |
| |
| The datasheet isn't very clear about what the tachometer reading is. |
| |
| An explanation from National Semiconductor: The two lower bits of the read |
| value have to be masked out. The value is still 16 bit in width. |
| |
| All temperature values are given in degrees Celsius. Resolution is 1.0 |
| degree for the local temperature, 0.125 degree for the remote temperature. |
| |
| The fan speed is measured using a tachometer. Contrary to most chips which |
| store the value in an 8-bit register and have a selectable clock divider |
| to make sure that the result will fit in the register, the LM63 uses 16-bit |
| value for measuring the speed of the fan. It can measure fan speeds down to |
| 83 RPM, at least in theory. |
| |
| Note that the pin used for fan monitoring is shared with an alert out |
| function. Depending on how the board designer wanted to use the chip, fan |
| speed monitoring will or will not be possible. The proper chip configuration |
| is left to the BIOS, and the driver will blindly trust it. |
| |
| A PWM output can be used to control the speed of the fan. The LM63 has two |
| PWM modes: manual and automatic. Automatic mode is not fully implemented yet |
| (you cannot define your custom PWM/temperature curve), and mode change isn't |
| supported either. |
| |
| The lm63 driver will not update its values more frequently than every |
| second; reading them more often will do no harm, but will return 'old' |
| values. |
| |