ASRock Rack X570D4U mainboard: I2C busses

This page describes the I2C busses and connected on-board devices on the ASRock X570D4U mainboard.

I2C bus 1

This bus is used for controlling on-board devices that are used when the host is on.

PCA9557 IO expander

Nuvoton NCT6796D-R SuperIO

This chip can read the CPU and chipset temperatures. It should be possible to use the newly added nct6775-i2c driver to use this device.

Alternatively the temperatures can be read using this shell script:

#!/bin/bash
i2cset -y 1 0x2d 0x4e 0x04
while :
do
    TSI0INT=$((16#$(i2cget -y 1 0x2d 0x09 | cut -f2 -dx)))
    TSI0FRC=$(($((16#$(i2cget -y 1 0x2d 0x0a | cut -f2 -dx)))>>5))
    TSI1INT=$((16#$(i2cget -y 1 0x2d 0x0b | cut -f2 -dx)))
    TSI1FRC=$(($((16#$(i2cget -y 1 0x2d 0x0c | cut -f2 -dx)))>>5))
    echo "TSI0_TEMP: $TSI0INT.$TSI0FRC °C / TSI1_TEMP: $TSI1INT.$TSI1FRC °C"
    sleep 0.5
done

Nuvoton W83773G

Temperature input 2 appears to be the mainboard temperature sensor.

cat /sys/class/hwmon/hwmon0/temp2_input

I2C bus 2

This bus is used for connecting to exernal power supplies with SMBus monitoring support.

I2C bus 3

This bus has an unknown purpose.

I2C bus 4

This bus is used to connect to expansion cards inserted into the PCI-Express slots of the mainboard.

NXP PCA9545A I2C bus switch

I2C bus 5

This bus is used for connecting to exernal power supplies with SMBus monitoring support.

I2C bus 7

This bus is used for connecting to the FRU EEPROM and the RAM DIMMs.

Unknown

Not tested yet.