The NXP i.MX8M Nano CPU has four I2C buses that operate at up to 400 Kbps. The CPU facilitates the functionality of both I2C master and slave according to the I2C Bus Specification v2.1, but the Linux kernel only contains an I2C bus master driver.
On the ConnectCore 8M Nano:
-
I2C1 connects internally to the power management IC (PMIC), the on-module Micro Controller Assist (MCA), and the Atmel Cryptochip at the following addresses:
Interface Address (7-bit) PMIC
0x4b
Cryptochip
0x60
MCA
0x63
On the ConnectCore 8M Nano Development Kit:
-
I2C2, I2C3 and I2C4 are available on the J48 expansion connector, where you can connect additional devices.
-
I2C2 is connected to the on-board audio chip, routed to the MIPI camera so it can connect to an image sensor and routed to the LVDS connector so it can connect to a touch controller.
Interface Address (7-bit) Maxim MAX98089 sound chip
0x10
Goodix touch controller
0x14
OmniVision CSI camera
0x3C
-
I2C2 is also available on the miniPCIe connector.
-
I2C3 (which operates at 1.8V) is connected to the on-board LT8912 MIPI-to-HDMI and SN65DSI83 MIPI-to-LVDS display bridges.
Interface Address (7-bit) SN65DSI83 MIPI-to-LVDS bridge
0x2C
LT8912 MIPI-to-HDMI bridge
0x48
-
I2C3 is also available on the HDMI connector, so it connects with HDMI monitors.
Kernel configuration
You can manage the I2C driver support through the kernel configuration:
-
IMX I2C interface (CONFIG_I2C_IMX)
This kernel configuration option is enabled as built-in on the default ConnectCore 8M Nano kernel configuration file.
Kernel driver
The driver for the I2C interface is located at:
| File | Description |
|---|---|
i.MX I2C controller driver |
Device tree bindings and customization
The i.MX8M Nano I2C interface device tree binding is documented at Documentation/devicetree/bindings/i2c/i2c-imx.txt.
The I2C interfaces are defined in the CPU, system-on-module, and carrier board device tree files.
Example: I2C3
Define the bus
i2c3: i2c@30a40000 {
#address-cells = <1>;
#size-cells = <0>;
compatible = "fsl,imx8mm-i2c", "fsl,imx21-i2c";
reg = <0x0 0x30a40000 0x0 0x10000>;
interrupts = <GIC_SPI 37 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clk IMX8MN_CLK_I2C3_ROOT>;
status = "disabled";
};Configure IOMUX
pinctrl_i2c3: i2c3grp {
fsl,pins = <
MX8MN_IOMUXC_I2C3_SCL_I2C3_SCL 0x400001c3
MX8MN_IOMUXC_I2C3_SDA_I2C3_SDA 0x400001c3
>;
};
pinctrl_i2c3_gpio: i2c3grp-gpio {
fsl,pins = <
MX8MN_IOMUXC_I2C3_SCL_GPIO5_IO18 0x1c3
MX8MN_IOMUXC_I2C3_SDA_GPIO5_IO19 0x1c3
>;
};Enable the bus and define attached client devices
&i2c3 {
clock-frequency = <100000>;
pinctrl-names = "default", "gpio";
pinctrl-0 = <&pinctrl_i2c3>;
pinctrl-1 = <&pinctrl_i2c3_gpio>;
scl-gpios = <&gpio5 18 GPIO_ACTIVE_HIGH>;
sda-gpios = <&gpio5 19 GPIO_ACTIVE_HIGH>;
status = "okay";
[...]
dsi_lvds_bridge: sn65dsi84@2c {
[...]
};
lt_bridge: lt8912@48 {
[...]
};
[...]
};Using the I2C bus
The I2C bus driver exposes device data through the sysfs at /sys/class/i2c-dev/.
|
The correct way to access an I2C device is through a kernel driver. Accessing the I2C bus from the file system can confuse your I2C bus and cause data loss on devices like EEPROMs. The following tools are recommended for debugging purposes only. |
I2C device interface
You can access I2C devices on an adapter from user space, through the /dev interface.
This support requires that you enable the kernel configuration option I2C device interface (CONFIG_I2C_CHARDEV).
Once you have enabled the option, you can use the /dev/i2c-N device node where N corresponds to the adapter number, starting at zero.
i2c-tools
You can install the i2c-tools package to access the I2C devices from user space. The package contains the following tools:
| Tool | Description |
|---|---|
i2cdetect |
Bus scanning |
i2cdump |
Device register dumping |
i2cget |
Device register reading |
i2cset |
Device register setting |
All I2C tools operate on a specific I2C bus which is identified by number.
To obtain a formatted list of all I2C adapters on your system, run:
~# i2cdetect -l i2c-3 i2c 30a40000.i2c I2C adapter i2c-4 i2c 30a50000.i2c I2C adapter i2c-2 i2c 30a30000.i2c I2C adapter i2c-0 i2c 30a20000.i2c I2C adapter
Query the I2C bus using the I2C bus number to find devices connected to that bus:
~# i2cdetect 0
i2cdetect: WARNING! This program can confuse your I2C bus
Continue? [y/N] y
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- UU -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: 60 -- -- UU -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
The example above shows several devices on the bus at addresses 0x4b, 0x60, and 0x63. The ones showing UU denote this address is currently in use by a driver, while devices without a registered driver show the address (in the example 0x60).
You can dump the registers of any of these devices using the i2cdump command with the I2C bus number as the first argument and the chip address as the second argument:
~# i2cdump 0 0x60
i2cdump: WARNING! This program can confuse your I2C bus
Continue? [y/N] y
0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef
00: XX XX XX 04 11 33 43 04 11 33 43 04 11 33 43 04 XXX??3C??3C??3C?
10: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
20: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
30: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
40: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
50: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
60: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
70: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
80: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
90: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
a0: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
b0: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
c0: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
d0: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
e0: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
f0: 11 33 43 04 11 33 43 04 11 33 43 04 11 33 43 04 ?3C??3C??3C??3C?
Accessing the I2C bus using Digi APIx
An example application called apix-i2c-example is included in the dey-examples-digiapix recipe (part of dey-examples package) of meta-digi layer. This application is an example of how to write data to an external EEPROM (24FC1026) and read it back using Digi APIx library on the ConnectCore 8M Nano platform.
Go to GitHub to see the application instructions and source code.
See I2C API for more information about the I2C APIx.
