ASRock Rack X570D4U mainboard: I2C busses

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

I2C bus 0

This bus is connected to the AUX_PANEL1 connector. SMBus alert for this bus is connected to GPIO 52 (G4) named input-aux-smb-alert-n.

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.

Using the NCT6775-I2C driver

The OpenBMC port for the X570D4U already includes the nct6775-i2c driver in it’s kernel, but as the SuperIO device only appears on the bus when the host system is powered on the driver needs to be loaded in and unloaded based on power state changes. This has not been implemented yet.

The driver can be manually loaded in using the following command:

echo "nct6775 0x2d" > /sys/bus/i2c/devices/i2c-1/new_device

If the driver was loaded correctly then you should now be able to find a folder called hwmon in the device folder /sys/bus/i2c/devices/i2c-1/1-002d. This folder will contain a symlink to the hwmon interface for the SuperIO chip. If the folder is missing then your kernel does not include the nct6775-i2c driver.

Directly accessing and reading the temperature registers

Alternatively the temperatures can be read using this shell script, for which no kernel driver is required:

#!/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

This device is available on the versions of the X570D4U which include a 10Gbit network adapter. It monitors the temperature of the 10Gbit NIC.

cat /sys/class/hwmon/hwmon0/temp2_input

I2C bus 2

This bus is used for connecting to exernal power supplies with SMBus monitoring support using the PSU_SMB1 connector. SMBus alert for this bus is connected to GPIO 54 (G6) named input-psu-smb-alert-n.

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 connected to the BMC_SMB_1 connector. The BMC_PRESENT_1_N signal on the BMC_SMB_1 connector is connected to GPIO 132 (Q4) named input-bmc-smb-present-n.

I2C bus 7

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

I2C bus 8

This bus is connected to the IPMB_1 connector.