| R.Marek@sh.cvut.cz | 7f15b66 | 2005-05-26 12:42:19 +0000 | [diff] [blame] | 1 | Kernel driver lm87 |
| 2 | ================== |
| 3 | |
| 4 | Supported chips: |
| 5 | * National Semiconductor LM87 |
| 6 | Prefix: 'lm87' |
| 7 | Addresses scanned: I2C 0x2c - 0x2f |
| 8 | Datasheet: http://www.national.com/pf/LM/LM87.html |
| 9 | |
| 10 | Authors: |
| 11 | Frodo Looijaard <frodol@dds.nl>, |
| 12 | Philip Edelbrock <phil@netroedge.com>, |
| 13 | Mark Studebaker <mdsxyz123@yahoo.com>, |
| 14 | Stephen Rousset <stephen.rousset@rocketlogix.com>, |
| 15 | Dan Eaton <dan.eaton@rocketlogix.com>, |
| 16 | Jean Delvare <khali@linux-fr.org>, |
| 17 | Original 2.6 port Jeff Oliver |
| 18 | |
| 19 | Description |
| 20 | ----------- |
| 21 | |
| 22 | This driver implements support for the National Semiconductor LM87. |
| 23 | |
| 24 | The LM87 implements up to three temperature sensors, up to two fan |
| 25 | rotation speed sensors, up to seven voltage sensors, alarms, and some |
| 26 | miscellaneous stuff. |
| 27 | |
| 28 | Temperatures are measured in degrees Celsius. Each input has a high |
| 29 | and low alarm settings. A high limit produces an alarm when the value |
| 30 | goes above it, and an alarm is also produced when the value goes below |
| 31 | the low limit. |
| 32 | |
| 33 | Fan rotation speeds are reported in RPM (rotations per minute). An alarm is |
| 34 | triggered if the rotation speed has dropped below a programmable limit. Fan |
| 35 | readings can be divided by a programmable divider (1, 2, 4 or 8) to give |
| 36 | the readings more range or accuracy. Not all RPM values can accurately be |
| 37 | represented, so some rounding is done. With a divider of 2, the lowest |
| 38 | representable value is around 2600 RPM. |
| 39 | |
| 40 | Voltage sensors (also known as IN sensors) report their values in |
| 41 | volts. An alarm is triggered if the voltage has crossed a programmable |
| 42 | minimum or maximum limit. Note that minimum in this case always means |
| 43 | 'closest to zero'; this is important for negative voltage measurements. |
| 44 | |
| 45 | If an alarm triggers, it will remain triggered until the hardware register |
| 46 | is read at least once. This means that the cause for the alarm may |
| 47 | already have disappeared! Note that in the current implementation, all |
| 48 | hardware registers are read whenever any data is read (unless it is less |
| 49 | than 1.0 seconds since the last update). This means that you can easily |
| 50 | miss once-only alarms. |
| 51 | |
| 52 | The lm87 driver only updates its values each 1.0 seconds; reading it more |
| 53 | often will do no harm, but will return 'old' values. |
| 54 | |
| 55 | |
| 56 | Hardware Configurations |
| 57 | ----------------------- |
| 58 | |
| 59 | The LM87 has four pins which can serve one of two possible functions, |
| 60 | depending on the hardware configuration. |
| 61 | |
| 62 | Some functions share pins, so not all functions are available at the same |
| 63 | time. Which are depends on the hardware setup. This driver assumes that |
| 64 | the BIOS configured the chip correctly. In that respect, it differs from |
| 65 | the original driver (from lm_sensors for Linux 2.4), which would force the |
| 66 | LM87 to an arbitrary, compile-time chosen mode, regardless of the actual |
| 67 | chipset wiring. |
| 68 | |
| 69 | For reference, here is the list of exclusive functions: |
| 70 | - in0+in5 (default) or temp3 |
| 71 | - fan1 (default) or in6 |
| 72 | - fan2 (default) or in7 |
| 73 | - VID lines (default) or IRQ lines (not handled by this driver) |