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- 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.
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