how to get a repeated start using zephyr I2c functions.

[weightwatcherphil]

I am using a nrf5340 and want to use I2c to talk to a LC709 battery charge IC.  I was able to do this 

using nrf_drv_twi_tx(..., ..., ..., ..., true);   to ger a repeated start and now I want to do it 

in zephyr.  I see the zephyr function 

i2c_burst_write_dt

but from the documentation i cannot tell if does a repeated start.

my question is does 

i2c_burst_write_dt

do repeated starts?

does it have a flag to cause repeated starts?

thanks,

Phil

[weightwatcherphil]

does the function 

static inline int i2c_write_read(const struct device *dev, uint16_t addr,

                 const void *write_buf, size_t num_write,

                 void *read_buf, size_t num_read)

do a repeated start ?

[weightwatcherphil]

attached is the actual I2C bus protocol i need.

LC709_I2c_bus_protocol.docx

thanks for your help.

[Raoul]

Hi Philip,

Try setting the I2C_MSG_RESTART flag for the Zephyr I2C driver. The Zephyr docs warn that "Not all I2C drivers have or require explicit support for this feature", but according to this line, the nrfx driver seems to take it into account.

You could try performing an i2c_write_read() with your sensor, with that flag set.

If you're new to using I2C through Zephyr, please check out this answer by my colleague:  How to use I2C on the nRF5340 DK ?

Best regards,

Raoul

[weightwatcherphil]

i have found that the I2 driver is really using the TWIM hardware and so now I am looking into how to use the 

nrfx_twim_xfer

function which as near as I can tell supports the repeated start option.

I will let you know how it turns out.  it will take me a day or two to implement it.

if you think it will not work let me know.

thanks

phil

[Raoul]

Hi,

Yep, I see from your newest ticket that you have started work on implementing the nrfx_twim driver.

I don't have experience with using that, I see that this case  RE: Continuous Background I2C process mentions NRFX_TWIM_FLAG_REPEATED_XFER in the context of repeated starts.

I hope that gets you further.

Best regards,

Raoul

[weightwatcherphil]

I am going to try an use the nrfx_twim_xfer function so you can close this ticket.

thanks

phil