Description¶

This chip is known to be used in the Zyxel NSA320 and NSA325 NAS Units andalso in some variants of the NSA310 but the driver has only been testedon the NSA320. In all of these devices it is connected to the same 3 GPIOlines which are used to provide chip select, clock and data lines. Theinterface behaves similarly to SPI but at much lower speeds than are normallyused for SPI.

Following each chip select pulse the chip will generate a single 32 bit wordthat 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 intenths of a degree.

sysfs-Interface¶

Notes¶

The access timings used in the driver are the same as used in the Zyxelprovided kernel. Testing has shown that if the delay between chip select andthe first clock pulse is reduced from 100 ms to just under 10ms then the chipwill not produce any output. If the duration of either phase of the clockis reduced from 100 us to less than 15 us then data pulses are likely to beread twice corrupting the output. The above analysis is based upon a sampleof one unit but suggests that the Zyxel provided delay values include areasonable tolerance.

The driver incorporates a limit that it will not check for updated valuesfaster than once a second. This is because the hardware takes a relatively longtime to read the data from the device and when it does it reads both temp andfan speed. As the most likely case for two accesses in quick succession isto read both of these values avoiding a second read delay is desirable.