How can I set a non-standard speed for the I2C bus using the Zephyr?

RE: How can I set a non-standard speed for the I2C bus using the Zephyr?

AlanIoT — Tue, 24 Sep 2024 12:07:41 GMT

For future reference and to anyone who might be interested, I found quite an easy hack to change the i2c bitrate:

this post explains a very easy hack to set the bitrate lower than 100kbps (Thank you Burt !)

Under `toolchainVersion > modules > hal > nordic > nrfx > mdk > nrf9160_bitfields.h` you can find the line

#define TWIM_FREQUENCY_FREQUENCY_K100 (0x01980000UL) /*!< 100 kbps */

Simply changing this value according this instruction was the solution to our problem. So I set the value to 10 kbps

#define TWIM_FREQUENCY_FREQUENCY_K100 (0x0028F000UL) /*!< 100 kbps */

and here you can see that the SCL ticks are 100 µs long (= 10kbps) and the sensor responds now.

We are reading a sensor hanging on an 8 meter long cable, which is impossible without lowering the bitrate to a much lower value.

RE: How can I set a non-standard speed for the I2C bus using the Zephyr?

Stefano1984 — Wed, 26 Jun 2024 13:46:04 GMT

I solved it like this:

((NRF_TWIM_Type *) NRF_TWIM1_BASE)->FREQUENCY = 0x00520000UL;

I wrote directly in the register, now the I2C module has a frequency of 20 KHz.

RE: How can I set a non-standard speed for the I2C bus using the Zephyr?

Kenneth — Thu, 18 Apr 2024 16:45:46 GMT

Hello,

An option may be to use the nrfx api directly (instead of the zephyr api), see twi examples here:
https://github.com/zephyrproject-rtos/hal_nordic/tree/master/nrfx/samples/src

If you need to use the zephyr api I don't see any other way than to modify the frequency register in between device_is_ready() and before you execute any twi transfers.

Kenneth