I2C write-restart-read issue on nRF Connect SDK v3.2.x

RE: I2C write-restart-read issue on nRF Connect SDK v3.2.x

Kazi Afroza Sultana — Fri, 23 Jan 2026 13:50:14 GMT

Hello,

That's the fix for now as there is bug in the "nordic,nrf-twi" driver in ncs v3.2.1.

RE: I2C write-restart-read issue on nRF Connect SDK v3.2.x

mt37 — Wed, 21 Jan 2026 18:44:22 GMT

l6e1 only works if I either add your fix, or if I run an older version of the SDK.

RE: I2C write-restart-read issue on nRF Connect SDK v3.2.x

David Hoover — Wed, 21 Jan 2026 16:23:02 GMT

Hi Kazi,

Thanks, that works! I am now observing the clock reading from the RTC chip, and the error code is 0.

Why does 'nordic,nrf-twi' work with previous versions of nRF Connect, and with all versions of Zephyr, but not with nRF Connect v3.2.x? Has the TWI driver been changed? Isn't TWI a legacy implementation? Is this a bug that will be fixed?

Why isn't TWIM the default implementation in the nrf52840dk/nrf52840 board?

Best,

David

RE: I2C write-restart-read issue on nRF Connect SDK v3.2.x

Kazi Afroza Sultana — Wed, 21 Jan 2026 14:49:30 GMT

Hello mt37,

Can you show me the error log?

Did you try to add the fix I mentioned in my (compatible = "nordic,nrf-twim";) reply? Also, you need to add bias-pull-up in the device tree file if you use internal pull-up resistor.

RE: I2C write-restart-read issue on nRF Connect SDK v3.2.x

mt37 — Fri, 16 Jan 2026 12:11:31 GMT

I think I have the same issue on SDK 3.2.1. I'm trying to complete the nRF Connect SDK Fundamentals lesson 6 exercise 1, and it's failing. My logic analyzer shows almost identical to yours. Address and single byte written get ACK, and then it returns with an error code, and lets the bus rise into "inactive" (no stop bit, no restart attempt).

I tried adding debugging I2C with CONFIG_I2C_LOG_LEVEL_DBG=y which didn't give me answers. I tried disabling the SPI interfaces, I tried both I2C0 and I2C1 with no change. I ensured there are no device tree IO pin conflicts with the I2C pins. I tried i2c_write_read_dt (from the exercise) as well as i2c_write_dt, and both look good on the logic analyzer (including ACK), but both missing the restart/stop. I tried on both an nRF52832 and nRF52840. I even tried skipping the zephyr I2C drivers and configuring the registers directly with nrfx_twim_init, nrfx_twim_enable, and nrfx_twim_xfer.

After several days of frustration and trying to track it down, I realized it works perfectly well on SDK 3.1.1, so something must have broken at 3.2.0 and/or 3.2.1

Edit: I also looked at the analog levels of the I2C signals to ensure they are crisp and well within voltage expectations, and even tried multiple sets of pullup resistors from ~910 ohms up to 10k ohms. Changing pullup resistors didn't seem to make any difference in the outcome (still failed the same), although I could see the corresponding changes to the rise time of the signals on the oscilloscope. 10k looks a little weak for my setup, but on SDK 3.1.1 it still works perfectly fine.

RE: I2C write-restart-read issue on nRF Connect SDK v3.2.x

Kazi Afroza Sultana — Thu, 15 Jan 2026 10:04:44 GMT

Hello,

Can you try the following overlay to use the ''nordic,nrf-twim'' driver?

&i2c1 {
    status = "okay";
    compatible = "nordic,nrf-twim"; <-- this line is added
    i2cclock: i2cclock@68 {
        compatible = "i2c-device";
        label = "I2CCLOCK";
        reg = <0x68>;
    };
};

RE: I2C write-restart-read issue on nRF Connect SDK v3.2.x

David Hoover — Wed, 14 Jan 2026 17:26:22 GMT

Hi, I am measuring the signals on P0.30 and P0.31.

If you don't have an rv3028 RTC connected to these pins, it's normal that it would fail in both cases. If you have another I2C peripheral handy, you can change the address in the device tree overlay (and perhaps slightly adapt the main.c to read some other registers) and try with your own peripheral.

RE: I2C write-restart-read issue on nRF Connect SDK v3.2.x

Kazi Afroza Sultana — Wed, 14 Jan 2026 12:34:34 GMT

Hello,

I have tried your sample on nRF52840dk (with modified C code and the device tree) for both NCS v2.1.1 and NCS v3.1.1. My system is windows.

Overlay file name: nrf52840dk_nrf52840.overlay

Build command: west build -p -b nrf52840dk/nrf5284

The application built and flashed ok.

I got same output for both version

In your application, you choose i2c1, so the SDA and SCL pin should show the output on the pin P 0.30 and P0.21 according to nRF52840 board file.

Can you please share which pins you are using for seeing SDA and SCL output on logic analyser?