How to configure I2C speed for STM32H7?

[fglau]

I am looking for a way to change the HAL I2C lib clock speed during runtime to either 100k or 400k or 1M.

I tried the following.....

hi2c1.Init.ClockSpeed = 100000;

However when compiling this the compiler do not recognize the parameter.

[fglau]

I forgot to mention - this is for the STM32H7 HAL I2C lib

[Tesla DeLorean]

You'd need to reintialize with the new values in the structure or disable the peripheral, change the clock parameters, and then enable again.​

[fglau]

Yes changing the speed and then calling MX_I2C1_Init(); again make sense - however

I cannot find the register for the STM32H7xx in the HAL I2C lib to set the new SCL clock rate.

I tried hi2c1.Init.ClockSpeed = 100000; but the Atollic compiler did not recognize the HAL parameter

Which parameter should i change to update the speed??

[Amel NASRI · Accepted solution]

Hi @fglau​ ,

The I2C speed configuration is based on I2C_TIMINGR register content.

So, in the HAL structure, you need to program properly the parameter hi2c1.Init.Timing:

hi2c1.Init.Timing      = I2C_TIMING;

I2C_TIMING value depends on:

• I2C clock source
• the speed you need to set
• rise and fall time
• filter's configuration

The appropriate value may be calculated using STM32CubeMX interface: you will see that a suitable value for TIMINGR will be suggested depending on what you provide as inputs.

-Amel

[fglau]

OK thanks Amel that worked just fine.

[RDums.1]

Hello @Amel NASRI​ 

where can I find the formula used by CubeMx to calculate I2C_TIMING?

Thanks.

[Amel NASRI]

Hello @RDums.1​ ,

I2C_TIMING calculation in STM32CubeMX is based on formulas described in the RM. You need to refer to I2C timing register (I2C_TIMINGR).

For any follow-up question, please submit a new discussion as the current one is old.

-Amel