I2C example for nrf52 DK board

[Timothy]

I have a nRF52 DK board and all is working fine. I can load the UART peripheral example and talk to my iPhone. I want to add I2C capability to connect to a temperature/Humidity sensor. I tried to run the i2c_api application and I get an error when it tries to build. It tells me to set the correct I2C device. How do I set the correct I2C device and how to I see the SCL and SDA I2C control pins on the external connector. Should they be on P0.26 and P0.27 pins. I was trying to get the i2c_api example working so I could understand how to use the I2c functions. I am very familiar with the I2C protocol. If you can tell me how to select the I2C device, initialize it, and do reads and writes so that SDA/SCL is active on the external connector pins I would be very appreciative. Thanks for you help. I am sure it is operator and error on my part. I am new to the nRF52 DK board.

#if DT_NODE_HAS_STATUS(DT_ALIAS(i2c_0), okay)

#define I2C_DEV_NODE    DT_ALIAS(i2c_0)

#elif DT_NODE_HAS_STATUS(DT_ALIAS(i2c_1), okay)

#define I2C_DEV_NODE    DT_ALIAS(i2c_1)

#elif DT_NODE_HAS_STATUS(DT_ALIAS(i2c_2), okay)

#define I2C_DEV_NODE    DT_ALIAS(i2c_2)

#else

#error "Please set the correct I2C device"

#endif

[runsiv]

Hi Timothy! 

If you are new to our environment I would recommending having a look at DevAcademy to get an overview over NCS. In the NCS fundamentals course we have a lesson covering I2C which you can find here. 

Regards

Runar

[Timothy]

Runar

I am not new to NCS. I have been using V1.7.0 with the nRF9160 for several years. I have I2C working fine in all of my examples. 

I am new to nrf52 and V2.5.0. I am using the i2c_api example. I have not changes anything. it has CONFIG_I2C=y set so I would expect that I2C would work as is. It says I have not set the correct device. what am I doing wrong? How do I set the correct device?

[khelmutlord]

Hello Timothy,

This is a blog post from one of our partners, Golioth, on using generic SPI devices. The process is similar for I2C devices.

https://blog.golioth.io/how-to-use-generic-spi-devices-with-zephyr/

The important thing is that each device on the I2C (or SPI as in the example above) bus has its own device tree node. You can define a "generic" node that can then be recognized by the build system and accessed by your application. This node will include parameters like its slave address and maximum frequency.

I would encourage you to look at a device tree snippet example of an I2C device, like this sensor:

https://github.com/zephyrproject-rtos/zephyr/blob/a2ad2d71f64b785a10e43f4feb81bf5f45503577/boards/arm/thingy53_nrf5340/thingy53_nrf5340_common.dtsi#L186

After everything has been defined in the devicetree, you can then get the node using "I2C_DT_SPEC_GET(DT_NODELABEL(<your_nodelabel>))" and use i2c_<operation>_dt function calls with that node.

https://docs.zephyrproject.org/latest/doxygen/html/group__i2c__interface.html

I am unable to find the i2c_api example--could you share a link so I could take a look?

Additionally, the "DT_ALIAS" macros are looking for a node in this style within your devicetree:

/ {
    aliases {
        i2c_0 = &i2c0;
    };
};

Let me know if this helps.

Thanks,

Helmut Lord

[Burt]

I think Tim is referring to the Zephyr SDK example zephyr/tests/drivers/i2c/i2c_api. Just my guess. My own question: is nRF Connect for VS Code the recommended way to build and run Zephyr SDK examples?

Burt

[Timothy]

I get the following  error if I set up the alias as you suggested. I created an overlay  that is exactly the lines above you said were needed. The error indicates that '_' is not allowed. what am I missing or doing wrong.

devicetree error: /aliases: alias property name 'i2c_0' should include only characters from [0-9a-z-]

[khelmutlord]

This catches me out sometimes. Try "i2c-0" instead. Devicetree -> macro translation does weird things with underscores and dashes. 

[khelmutlord]

nRF Connect in VS Code is a fine way to build Zephyr examples. You could also use west, Zephyr's build utility, since this is basically what the extension does under the hood. nRF Connect is a superset of Zephyr features so there's no issue building anything in Zephyr w/ nRF Connect. 

[Burt]

Thanks, Helmut. Yeah, I like building with west--I often use one of my Windows laptops and building under nRF Connect for VS Code seems to take a bigger performance hit than if I use a Mac or Linux computer.

Burt

[Timothy]

when I replace "i2c_0" with "i2c-0" I can build and flash but things still fail. I am running the V2.5.0/zephyr/test/drivers/i2c_api example. when it looks for 

#if DT_NODE_HAS_STATUS(DT_ALIAS(i2c_0), okay)

#define I2C_DEV_NODE    DT_ALIAS(i2c_0)

#elif DT_NODE_HAS_STATUS(DT_ALIAS(i2c_1), okay)

#define I2C_DEV_NODE    DT_ALIAS(i2c_1)

#elif DT_NODE_HAS_STATUS(DT_ALIAS(i2c_2), okay)

#define I2C_DEV_NODE    DT_ALIAS(i2c_2)

#else

#error "Please set the correct I2C device"

#endif

it finds i2c_0. I do not know why it now finds the underscore. when I go to run it I get the error shown below. I added test messages. so it says it initialized the I2C peripheral, wrote a config setting but failed when it went to read the config back. any idea what is going on now? I am very comfortable with the I2C protocol. I have been writing I2C drivers for all kinds of devices for a very long time. If I can get SCL and SDA to external pins and have them execute the I2C protocol I will be able to connect my devices to the I2C bus. Is there a simpler I2C example like blinky that just sends reads or writes to the I2C bus?

*** Booting nRF Connect SDK v2.5.0 ***
Running TESTSUITE i2c_gy271
===================================================================
START - test_i2c_burst_gy271
I2C device is ready
I2C config passed
I2C get_config failed

[Timothy]

any idea how I can get I2C interface to work? I cannot proceed until the I2C interface is working.

[runsiv]

Hi,

Can you provide your devicetree overlay? Just in general the troubleshooting devicetree section here is a good read. It also covers your question regarding underscore 

"

• In C/C++, devicetree names must be lowercased and special characters must be converted to underscores. Zephyr’s generated devicetree header has DTS names converted in this way into the C tokens used by the preprocessor-based <devicetree.h> API.

• In overlays, use devicetree node and property names the same way they would appear in any DTS file. Zephyr overlays are just DTS fragments.

A former support member made this example a while back, an simple I2C scanner, I would have a look at it just to compare the overlays. 

Regards

Runar

[Timothy]

if I compile i2c_api application with overlay as follows

/ {
aliases {
i2c-0 = &i2c0;
};
};

I can build and run but I get the following errors. I2C does not work. This is the provided standard test in V2.5.0/zephyr/tests/devices. can someone tell me what I have to do to get it running on the nrf52 DK board. the errors are the following:

*** Booting nRF Connect SDK v2.5.0 ***
Running TESTSUITE i2c_gy271
===================================================================
START - test_i2c_burst_gy271
I2C get_config failed

Assertion failed at ../src/test_i2c.c:159: i2c_gy271_test_i2c_burst_gy271: test_burst_gy271() == TC_PASS is false

FAIL - test_i2c_burst_gy271 in 0.013 seconds
===================================================================
START - test_i2c_gy271
I2C get_config failed

Assertion failed at ../src/test_i2c.c:154: i2c_gy271_test_i2c_gy271: test_gy271() == TC_PASS is false

FAIL - test_i2c_gy271 in 0.012 seconds
===================================================================
TESTSUITE i2c_gy271 failed.

------ TESTSUITE SUMMARY START ------

SUITE FAIL - 0.00% [i2c_gy271]: pass = 0, fail = 2, skip = 0, total = 2 duration = 0.025 seconds
- FAIL - [i2c_gy271.test_i2c_burst_gy271] duration = 0.013 seconds
- FAIL - [i2c_gy271.test_i2c_gy271] duration = 0.012 seconds

------ TESTSUITE SUMMARY END ------

===================================================================
PROJECT EXECUTION FAILED