How to use I2C receive continue in Zephyr without restarting the transaction (without another start bit)?

RE: How to use I2C receive continue in Zephyr without restarting the transaction (without another start bit)?

Hung Bui — Thu, 13 Mar 2025 15:29:41 GMT

Hi,

My understanding is that if you don't define I2C_MSG_STOP , then between the bytes it will not generate STOP but at the last byte it will generate a STOP. I think it's mandated by the I2C Spec:

https://www.nxp.com/docs/en/user-guide/UM10204.pdf

There is some ongoing discussion here, not 100% sure if it's relevant to what you want to do though:
github.com/.../76660

RE: How to use I2C receive continue in Zephyr without restarting the transaction (without another start bit)?

Abdelrahman — Thu, 13 Mar 2025 12:59:10 GMT

There is my implementation

gsi2c_msg.buf = (char *)pu8_buf;

gsi2c_msg.len = (uint32_t) u16_len;

gsi2c_msg.flags = I2C_MSG_WRITE | (b_stop ? I2C_MSG_STOP : 0);

printf("I2C Sending to 0x%X: ", u16_addr);

for (uint16_t i = 0; i < u16_len; i++)

{

printf("0x%02X ", pu8_buf[i]);

}

printf("\n");

s32_retval = i2c_transfer(gpstr_internal_i2c_dev , &gsi2c_msg , 1 , u16_addr);

b_stop is used for choosing to send stop bit or not.

I sent the first byte with b_stop = 0

then the second byte with b_stop = 1

after the first byte the transaction stop:

I found this on the https://docs.zephyrproject.org/latest/

Is that mean "i2c_transfer" will always stop the transaction?

Is there any API I can use to continue the receiving without starting a new transaction?

RE: How to use I2C receive continue in Zephyr without restarting the transaction (without another start bit)?

morrison2 — Tue, 11 Mar 2025 10:04:52 GMT

Thanks for the clarification! I’d love to see how you implement the I2C_MSG_STOP flag in your code. A simple example would really help us troubleshoot! sprunki phase 3

RE: How to use I2C receive continue in Zephyr without restarting the transaction (without another start bit)?

Hung Bui — Tue, 11 Mar 2025 08:27:13 GMT

Hi Abdelrahman,
In theory if you set the flag I2C_MSG_STOP it should therefore set the flag NRFX_TWIM_FLAG_TX_NO_STOP in nrfx_twim driver. Then instead of connecting the SHORT LAST_TX to STOP task, it will connect the shot LAST_TX to SUSPEND task instead.
Could you show how you do it in the code ? Maybe provide us a simple application so we can try to reproduce the issue here.
Another option is to use nrfx driver directly, the samples can be found in \modules\hal\nordic\nrfx\samples\src\nrfx_twim_twis