Many ASUS motherboards do not publish all the available sensors via the Super I/O chip but the missing ones are available through the embedded controller (EC) registers.

This driver (unlike the wmi-based one) reads sensor values directly from the EC using the ec kernel module. However, to ensure no race between this driver and the firmware, it locks the same mutex used by the WMI functions when accessing EC. This mutex has the same name (\AMW0.ASMX) for all ASUS boards author seen DSDT code from (a bit more then 10 models).

The EC registers do not provide critical values for the sensors and as such they are not published to the HWMON.

1. Pro WS X570-ACE
2. ROG CROSSHAIR VIII HERO
3. ROG CROSSHAIR VIII HERO (WI-FI)
4. ROG CROSSHAIR VIII DARK HERO
5. ROG CROSSHAIR VIII FORMULA
6. ROG STRIX B550-E GAMING
7. ROG STRIX B550-I GAMING
8. ROG STRIX X570-E GAMING
9. ROG STRIX X570-F GAMING
10. ROG STRIX X570-I GAMING

First, you need to obtain ACPI DSDT source for your board. You can get it from /sys/firmware/acpi/tables/DSDT in the binary form and decompile using the iasl tool from the acpica package:

$ sudo cat /sys/firmware/acpi/tables/DSDT > dsdt.dat
$ iasl dsdt.dat

This will produce decompiled file dsdt.dsl which you need to read and gather some information from it. Find a function named BREC. Its declaration starts with Method (BREC, 1. This is the WMI function to read EC registers ("Block Read EC" or something). If the function is a dummy one, like this:

Method (BREC, 1, Serialized)
{
       Return (Ones)
}

your motherboard probably does not publish any sensors in the EC. If the function contains meaningful code, read through it a bit. Not far from the beginning it should contain a command to lock a mutex. The command in the AML (the language of the ACPI code) is named Acquire and the instructions should look like If ((Acquire (ASMX, 0xFFFF) == Zero)). You need the name of the mutex, here it is "ASMX". Now find its declaration (Mutex (ASMX, 0x00)). It will be declared inside a scope, with the scope declaration looking as Device (<Device name>), find the closest one to the mutex declaration towards the top of the file. Now compose the full name of the mutex, which starts from the '' and then consists of device name(s) and the mutex name. In the example above the name is \AMW0.ASMX. If you get another name, write it down as you will need it later.

Now find out which EC registers to read (although they are pretty typical). If you have no idea is there any, you can try the hwinfo software under Windows that will show the EC node and known sensors for it. When you have the data (or decided to probe the default set), the following changes to the source code need to be made:

1. Add your board vendor and name to the asus_ec_dmi_table array and a new enum value to the board enum. You can find the board vendor and the board name in /sys/class/dmi/id/board_vendor and /sys/class/dmi/id/board_name or using dmidecode.

2. Add new entry to the known_boards array where list sensors for the board and the path for the ACPI mutex which is used by the firmware to lock access to the EC. You can find this path in the BREC function, look for Acquire() call near the top of the function.

Example: If ((Acquire (ASMX, 0xFFFF) == Zero)). The mutex name is ASMX, and since the BREC method is inside the AMW0 object, the mutex path is \AMW0.ASMX.

3. If you discover new sensors, modify the known_ec_sensor enum and add it to the known_ec_sensors array. For each sensor you need to provide its size in bytes (for example, RPM counters span two single-byte registers), its bank index and register index within the bank. If the sensor spans two or more registers, provide the first one (the smaller number).

Compile and it should work.