Need to change I2C bus speed to 50KHz

RE: Need to change I2C bus speed to 50KHz

JFC — Wed, 31 Jul 2024 19:47:29 GMT

Got it - thanks!

RE: Need to change I2C bus speed to 50KHz

Turbo J — Tue, 30 Jul 2024 05:42:09 GMT

Look for i2c_bitbang and i2c_gpio in the driver sources.Needs to be configured via devicetree as "gpio-i2c".

I only see an example for spi bitbang in the samples.

RE: Need to change I2C bus speed to 50KHz

JFC — Mon, 29 Jul 2024 19:02:42 GMT

Thanks for the suggestion, Turbo J. I didn't find the software-only driver. If you can share a pointer to it, I'll look it over. A supported option would be nice to have.

Thanks,

Jim

RE: Need to change I2C bus speed to 50KHz

JFC — Mon, 29 Jul 2024 19:01:44 GMT

Thanks for those helpful tips. I reverted the hack and added the code and the display is stable. Very helpful. I also sent a note to the manufacturer asking why the device was limited to 50KHz.

Thanks again for your quick help.

Jim

RE: Need to change I2C bus speed to 50KHz

Jørgen Holmefjord — Mon, 29 Jul 2024 14:07:12 GMT

After i2c_configure(), try adding this line:

NRF_TWIM1->FREQUENCY = 0x00C80000;

You will have to change the TWIM instance number if you are using a different instance (e.g. NRF_TWIM2 for instance 2).

[quote user="JFC"]On a side note, why not make sub-100K frequencies available via the SDK? Can that be a feature request?[/quote]

The chip HW have not been designed to support other frequencies and they are not tested/verified. Most I2C devices supports 100kHz or above.

RE: Need to change I2C bus speed to 50KHz

Turbo J — Sat, 27 Jul 2024 06:03:25 GMT

Zephyr (nRF connect SDK) ships a software I²C driver that only requires two GPIO ports, try using that when you need to run this slow.

IIRC it does not support clock stretching out-of-the-box.

RE: Need to change I2C bus speed to 50KHz

JFC — Fri, 26 Jul 2024 20:58:11 GMT

Thanks Jørgen.

I confirmed that bus speed is the problem with this peripheral after changing the 100KHz value in nrf9160_bitfields.h from 0x01980000 to 0x00C80000. It's rock-steady with this change.

I'm afraid I don't know how to access the FREQUENCY register - can you point me to an example? I've got minimal interaction with the device in my LCD interface:

static const struct i2c_dt_spec i2c_dev = I2C_DT_SPEC_GET(I2C_INST);

That's all I have that references the I2C driver. Unfortunately, I don't know how to follow this reference all the way to the FREQUENCY register.

On a side note, why not make sub-100K frequencies available via the SDK? Can that be a feature request?

Thanks,

Jim

RE: Need to change I2C bus speed to 50KHz

Jørgen Holmefjord — Fri, 26 Jul 2024 10:57:49 GMT

Hi,

The I2C driver will throw an error if you try to configure anything else than the supported speeds. It will not be possible to configure this through the APIs in nRF Connect SDK or Zephyr. If you need to try out different speeds, you will have to write directly to the FREQUENCY register of the TWI(M) peripheral, after configuration and before transmits. Note that only the defined speeds mentioned in the register documentation (100K/250K/400K) is supported and tested, all other values are used at your own risk. We do not provide register values for other speeds.

Best regards,
Jørgen