0001 Kernel driver nsa320_hwmon
0002 ==========================
0003
0004 Supported chips:
0005
0006 * Holtek HT46R065 microcontroller with onboard firmware that configures
0007
0008 it to act as a hardware monitor.
0009
0010 Prefix: 'nsa320'
0011
0012 Addresses scanned: none
0013
0014 Datasheet: Not available, driver was reverse engineered based upon the
0015
0016 Zyxel kernel source
0017
0018
0019
0020 Author:
0021
0022 Adam Baker <linux@baker-net.org.uk>
0023
0024 Description
0025 -----------
0026
0027 This chip is known to be used in the Zyxel NSA320 and NSA325 NAS Units and
0028 also in some variants of the NSA310 but the driver has only been tested
0029 on the NSA320. In all of these devices it is connected to the same 3 GPIO
0030 lines which are used to provide chip select, clock and data lines. The
0031 interface behaves similarly to SPI but at much lower speeds than are normally
0032 used for SPI.
0033
0034 Following each chip select pulse the chip will generate a single 32 bit word
0035 that contains 0x55 as a marker to indicate that data is being read correctly,
0036 followed by an 8 bit fan speed in 100s of RPM and a 16 bit temperature in
0037 tenths of a degree.
0038
0039
0040 sysfs-Interface
0041 ---------------
0042
0043 ============= =================
0044 temp1_input temperature input
0045 fan1_input fan speed
0046 ============= =================
0047
0048 Notes
0049 -----
0050
0051 The access timings used in the driver are the same as used in the Zyxel
0052 provided kernel. Testing has shown that if the delay between chip select and
0053 the first clock pulse is reduced from 100 ms to just under 10ms then the chip
0054 will not produce any output. If the duration of either phase of the clock
0055 is reduced from 100 us to less than 15 us then data pulses are likely to be
0056 read twice corrupting the output. The above analysis is based upon a sample
0057 of one unit but suggests that the Zyxel provided delay values include a
0058 reasonable tolerance.
0059
0060 The driver incorporates a limit that it will not check for updated values
0061 faster than once a second. This is because the hardware takes a relatively long
0062 time to read the data from the device and when it does it reads both temp and
0063 fan speed. As the most likely case for two accesses in quick succession is
0064 to read both of these values avoiding a second read delay is desirable.
