I2C

The Inter-Integrated Circuit (I2C) interface is a two-wire, bidirectional serial bus that provides a simple and efficient method for data exchange among devices. The phyFLEX-AM62Px provides independent multimaster fast-mode I2C modules. This guide will show you how to test the I2C interface on the phyFLEX-Libra AM62Px.

Note

Only a subset of I2C interfaces are supported on the phyFLEX-Libra AM62Px by default but others can be enabled via pin multiplexing.

I2C Settings

Hardware Interface

sysfs Path

WKUP_I2C0

/dev/i2c-1

I2C0

/dev/i2c-2

I2C1

/dev/i2c-3

I2C2

/dev/i2c-4

Scanning the I2C Buses

  • Power on the phyFLEX-Libra AM62Px and boot into Linux.

  • List the available I2C devices. Each /dev/i2c-* entry corresponds to one of the I2C interfaces in the table above.

List I2C devices
am62pxx-phyflex-libra-rdk-1:~# ls /dev/i2c*

  • Use the i2cdetect command to scan each bus for devices. WKUP_I2C0 carries the SOM’s own devices (PMIC, VDD_CORE regulator, EEPROM, RTC). I2C0, I2C1 and I2C2 carry the carrier-board peripherals.

Scan WKUP_I2C0 bus (SOM devices)
am62pxx-phyflex-libra-rdk-1:~# i2cdetect -y -r 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: UU -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: UU -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: UU -- UU -- -- -- -- -- 58 -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
Scan I2C0 bus (carrier board devices)
am62pxx-phyflex-libra-rdk-1:~# i2cdetect -y -r 2
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- UU -- -- -- -- -- -- -- -- -- 2b -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- UU UU -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
Scan I2C1 bus (carrier board devices)
am62pxx-phyflex-libra-rdk-1:~# i2cdetect -y -r 3
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- UU -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- 47 -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- 62 -- -- -- -- -- -- -- -- -- -- -- -- --
70: 70 -- -- -- -- -- -- --
Scan I2C2 bus (carrier board devices)
am62pxx-phyflex-libra-rdk-1:~# i2cdetect -y -r 4
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- UU
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Note

UU indicates that the device with that particular address is tied to a kernel driver and you will be unable to communicate with the device via i2c commands (i2cset and i2cget).

The devices on each bus correspond to:

WKUP_I2C0 addresses (SOM devices)

Interface

Address (7-bit)

PMIC TPS65219 (U6)

0x30

VDD_CORE Regulator TPS62870 (U7)

0x40

SOM EEPROM M24C32 (U8)

0x50

SOM EEPROM M24C32 (U8), identification page

0x58

RTC RV-3028-C7 (U11)

0x52
I2C0 addresses (carrier board devices)

Interface

Address (7-bit)

GPIO Expander TCAL6416 (U58)

0x21

USB PD Controller STUSB4500 (U1)

0x2B

Factory EEPROM M24C02 (U57)

0x51

User EEPROM M24C02 (U80)

0x52
I2C1 addresses (carrier board devices)

Interface

Address (7-bit)

GPIO Expander TCAL6416 (U72)

0x21

USB-C Mux HD3SS3220 (U66)

0x47

RGB LED Controller PCA9633 (U55)

0x62

RGB LED Controller PCA9633 (U55), All Call address

0x70
I2C2 addresses (carrier board devices)

Interface

Address (7-bit)

Temperature Sensor P3T1750 (U56)

0x4F

Camera, display and SFP+ modules connected to the phyFLEX-Libra AM62Px add further devices to I2C0, I2C1 and MCU_I2C0.

Note

The list of visible I2C devices in your output may differ from what is shown above. This is because our System on Modules (SoMs) come in different variants, and some devices (like the RTC) are optional depending on the specific variant you are using.

Temperature Sensor

The phyFLEX-Libra AM62Px features an NXP P3T1750 digital temperature sensor (U56) on I2C2 (/dev/i2c-4, address 0x4F). It measures the temperature of the carrier board. Linux exposes the sensor through the hardware monitoring (hwmon) subsystem. For the temperature sensors inside the AM62Px processor, see Thermal Zone.

  • Each hwmon device has a name attribute. Find the hwmon device that belongs to the P3T1750:

    am62pxx-phyflex-libra-rdk-1:~# grep -l p3t1755 /sys/class/hwmon/hwmon*/name

  • Read the temperature from the temp1_input attribute of that hwmon device (replace hwmonX with the device found above):

    am62pxx-phyflex-libra-rdk-1:~# cat /sys/class/hwmon/hwmonX/temp1_input

    The value is in millidegrees Celsius. For example, a value of 32125 means 32.125°C.

  • The driver also provides the temp1_max and temp1_max_hyst attributes, which set the sensor’s over-temperature limit and hysteresis (also in millidegrees Celsius).