I2C application (app/i2c-app.c)

Table of Contents

• Jetson TX2
• Jetson AGX
• Jetson NX

I2C application demonstrates how to access/manipulate Always On (AON) I2C from the SPE/AON processor. I2C 2, 8 and 10 are in AON domain for Jetson TX2, Jetson AGX and Jetson NX.

The ENABLE_I2C_APP flag in the soc/*/target_specific.mk file controls compilation of this demo app.

Note

1) It is required to compile device tree and flash board to have them updated after making kernel device tree changes as described in following sections.

2) Jetson NX has a common pin (Pin 27) which is shared by both GPIO APP and I2C APP, hence GPIO APP and I2C APP cannot be enabled simultaneously.

Jetson TX2

The sample app uses I2C bus 2 and BMI160 sensor module for demo purposes. Make sure I2C bus 2 is disabled in linux kernel as shown below in tegra186-quill-p3310-1000-c03-00-base.dts device tree file.

i2c@c240000 {
        status = "disabled";
};

In addition to above device tree file, make sure bus@1 is being removed from the tegra186-quill-p3310-1000-a00-plugin-manager.dtsi file as well as shown in below code snippet.

bus@1 {
        i2c-bus = <&gen2_i2c>;
        eeprom@0 {
                slave-address = <0x51>;
        };
};

BMI160 module is similar to the sample app available at:

https://hackspark.fr/en/electronics/1341-6dof-bosch-6-axis-acceleration-gyro-gravity-sensor-gy-bmi160.html

The I2C app accesses the 40 pin header J21 and expects I2C external module at the pin map shown below:

• Pin 1 - 3.3V
• Pin 3 - SDA
• Pin 5 - SCL
• Pin 39, 25 - GND

The demo app reads BMI160 sensor ID. If the app successfully retrieves the correct ID, it prints the following message:

I2C test successful, sendor ID: 0xd1

Note

BMI160 is configured to have the I2C address 0x68 by connecting its SDO pin to GND.

Jetson AGX

The sample app uses I2C bus 8 and on board audio codec chip for demo purposes. Make sure access to codec chip and I2C bus 8 from other software stacks like kernel/bootloader etc... is disabled. For kernel, related dts is tegra194-audio-p2822-0000.dtsi and below is the sample snippet to disable:

i2c@c250000 {
        status = "disabled";
        rt5658: rt5659.7-001a@1a {
                compatible = "realtek,rt5658";
                reg = <0x1a>;

                realtek,jd-src = <RT5659_JD_NULL>;
                realtek,dmic1-data-pin = <RT5659_DMIC1_NULL>;
                realtek,dmic2-data-pin = <RT5659_DMIC2_DATA_IN2P>;

                gpios = <&tegra_main_gpio TEGRA194_MAIN_GPIO(S, 5) 0>;

                status = "disabled";
        };
};

The demo app reads device ID. Test is successful if app retrieves correct ID and should print "I2C test successful".

Jetson NX

The sample app uses I2C bus 2 and LSM303 sensor module for demo purposes. Make sure I2C bus 2 is disabled in linux kernel as shown below in tegra194-p3668-common.dtsi device tree file.

i2c { status = "disabled"; };

The flag ENABLE_SPE_FOR_NX has to enabled in the soc/t19x/target_specific.mk to access AON I2C LSM303 module is similar to the sample app available at: https://www.adafruit.com/product/1120

The I2C app accesses the 40 pin header and expects I2C external module at the pin map shown below:

• Pin 1 - 3.3V
• Pin 27 - SDA
• Pin 28 - SCL
• Pin 25 - GND

The demo app reads Control Register of LSM303 sensor. The default value of the register is 0x7. If the app successfully retrieves the correct value of the register, it prints the following message:

I2C test successful