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Commit | Line | Data |
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630300d5 AB |
1 | Kernel driver nsa320_hwmon |
2 | ========================== | |
3 | ||
4 | Supported chips: | |
5 | * Holtek HT46R065 microcontroller with onboard firmware that configures | |
6 | it to act as a hardware monitor. | |
7 | Prefix: 'nsa320' | |
8 | Addresses scanned: none | |
9 | Datasheet: Not available, driver was reverse engineered based upon the | |
10 | Zyxel kernel source | |
11 | ||
12 | Author: | |
13 | Adam Baker <linux@baker-net.org.uk> | |
14 | ||
15 | Description | |
16 | ----------- | |
17 | ||
18 | This chip is known to be used in the Zyxel NSA320 and NSA325 NAS Units and | |
19 | also in some variants of the NSA310 but the driver has only been tested | |
20 | on the NSA320. In all of these devices it is connected to the same 3 GPIO | |
21 | lines which are used to provide chip select, clock and data lines. The | |
22 | interface behaves similarly to SPI but at much lower speeds than are normally | |
23 | used for SPI. | |
24 | ||
25 | Following each chip select pulse the chip will generate a single 32 bit word | |
26 | that contains 0x55 as a marker to indicate that data is being read correctly, | |
27 | followed by an 8 bit fan speed in 100s of RPM and a 16 bit temperature in | |
28 | tenths of a degree. | |
29 | ||
30 | ||
31 | sysfs-Interface | |
32 | --------------- | |
33 | ||
34 | temp1_input - temperature input | |
35 | fan1_input - fan speed | |
36 | ||
37 | Notes | |
38 | ----- | |
39 | ||
40 | The access timings used in the driver are the same as used in the Zyxel | |
41 | provided kernel. Testing has shown that if the delay between chip select and | |
42 | the first clock pulse is reduced from 100 ms to just under 10ms then the chip | |
43 | will not produce any output. If the duration of either phase of the clock | |
44 | is reduced from 100 us to less than 15 us then data pulses are likely to be | |
45 | read twice corrupting the output. The above analysis is based upon a sample | |
46 | of one unit but suggests that the Zyxel provided delay values include a | |
47 | reasonable tolerance. | |
48 | ||
49 | The driver incorporates a limit that it will not check for updated values | |
50 | faster than once a second. This is because the hardware takes a relatively long | |
51 | time to read the data from the device and when it does it reads both temp and | |
52 | fan speed. As the most likely case for two accesses in quick succession is | |
53 | to read both of these values avoiding a second read delay is desirable. |