| Kernel driver nsa320_hwmon | |
| ========================== | |
| Supported chips: | |
| * Holtek HT46R065 microcontroller with onboard firmware that configures | |
| it to act as a hardware monitor. | |
| Prefix: 'nsa320' | |
| Addresses scanned: none | |
| Datasheet: Not available, driver was reverse engineered based upon the | |
| Zyxel kernel source | |
| Author: | |
| Adam Baker <linux@baker-net.org.uk> | |
| Description | |
| ----------- | |
| This chip is known to be used in the Zyxel NSA320 and NSA325 NAS Units and | |
| also in some variants of the NSA310 but the driver has only been tested | |
| on the NSA320. In all of these devices it is connected to the same 3 GPIO | |
| lines which are used to provide chip select, clock and data lines. The | |
| interface behaves similarly to SPI but at much lower speeds than are normally | |
| used for SPI. | |
| Following each chip select pulse the chip will generate a single 32 bit word | |
| that contains 0x55 as a marker to indicate that data is being read correctly, | |
| followed by an 8 bit fan speed in 100s of RPM and a 16 bit temperature in | |
| tenths of a degree. | |
| sysfs-Interface | |
| --------------- | |
| temp1_input - temperature input | |
| fan1_input - fan speed | |
| Notes | |
| ----- | |
| The access timings used in the driver are the same as used in the Zyxel | |
| provided kernel. Testing has shown that if the delay between chip select and | |
| the first clock pulse is reduced from 100 ms to just under 10ms then the chip | |
| will not produce any output. If the duration of either phase of the clock | |
| is reduced from 100 us to less than 15 us then data pulses are likely to be | |
| read twice corrupting the output. The above analysis is based upon a sample | |
| of one unit but suggests that the Zyxel provided delay values include a | |
| reasonable tolerance. | |
| The driver incorporates a limit that it will not check for updated values | |
| faster than once a second. This is because the hardware takes a relatively long | |
| time to read the data from the device and when it does it reads both temp and | |
| fan speed. As the most likely case for two accesses in quick succession is | |
| to read both of these values avoiding a second read delay is desirable. |