How to remove start bit from an I2C transfer in zephyr

[jspiller]

Hello,

I am developing a driver for the vl53l5cx TOF sensor from ST, however their sequential write format looks as such:

This is problematic for me since I can get the address, and register index sent correctly with the stop bit at the end, however zephyr always sends a start bit for the data being written and I have not found a way to disable this. How can I do this using sdk 1.9.1?

Thanks,

Jacob

[gweis]

Hey,
Can you please share your driver for vl53l5cx on zephyr?
I'm interested in it too.
Thanks!

[jspiller]

Turns out there was an error in their datasheet and it should comply with the usual I2C spec. I filled the WrMulti and RdMulti the following way:

uint8_t RdMulti(
	VL53L5CX_Platform *p_platform,
	uint16_t RegisterAddress,
	uint8_t *p_values,
	uint32_t num_read)
{
	uint8_t status = 0;
	int offset = 0;

	while (num_read > 0)
	{
		writeBuf[0] = (RegisterAddress >> 8) & 0xFF;
		writeBuf[1] = RegisterAddress & 0xFF;

		if (num_read >= MAX_RX_BUFFER)
		{
			status |= i2c_write(p_platform->i2c_dev, writeBuf, 2U, p_platform->address);
			status |= i2c_read(p_platform->i2c_dev, p_values + offset, MAX_RX_BUFFER, p_platform->address);

			num_read -= MAX_RX_BUFFER;
			RegisterAddress += MAX_RX_BUFFER;
			offset += MAX_RX_BUFFER;
		}
		else
		{
			status |= i2c_write(p_platform->i2c_dev, writeBuf, 2U, p_platform->address);
			status |= i2c_read(p_platform->i2c_dev, p_values + offset, num_read, p_platform->address);
			break;
		}
	}

	return (status);
}

uint8_t WrMulti(
	VL53L5CX_Platform *p_platform,
	uint16_t RegisterAddress,
	uint8_t *p_values,
	uint32_t num_write)
{
	uint8_t status = 0;
	uint32_t offset = 0;

	while (num_write > 0)
	{
		writeBuf[0] = (RegisterAddress >> 8) & 0xFF;
		writeBuf[1] = RegisterAddress & 0xFF;
		memcpy(&(writeBuf[2]), &(p_values[offset]), (MAX_TX_BUFFER - 2));

		if (num_write >= (MAX_TX_BUFFER - 2))
		{
			status |= i2c_write(p_platform->i2c_dev, writeBuf, MAX_TX_BUFFER, p_platform->address);

			num_write -= (MAX_TX_BUFFER - 2);
			RegisterAddress += (MAX_TX_BUFFER - 2);
			offset += (MAX_TX_BUFFER - 2);
		}
		else
		{
			status |= i2c_write(p_platform->i2c_dev, writeBuf, num_write + 2, p_platform->address);
			break;
		}
	}

	return (status);
}

and WrByte/RdByte work in the same way just without the while loop since the size is only 1.

[Richard Osterloh]

I'm struggling with this part in Zephyr too and am trying to test your solution. Have you defined writeBuf, MAX_TX_BUFFER and MAX_RX_BUFFER globally somewhere? I was using a similar implementation to your earlier one but something is definitely wrong

uint8_t RdMulti(VL53L5CX_Platform *p_platform, uint16_t RegisterAdress, uint8_t *p_values,
		uint32_t size)
{
	uint8_t data_write[2];

	sys_put_be16(RegisterAdress, data_write);

	return i2c_write_read_dt(p_platform->i2c, data_write, sizeof(data_write),
				 p_values, size);
}

uint8_t WrMulti(VL53L5CX_Platform *p_platform, uint16_t RegisterAdress, uint8_t *p_values,
		uint32_t size)
{
	struct i2c_msg msg[2];
	uint8_t data_write[2];

	sys_put_be16(RegisterAdress, data_write);

	msg[0].buf = data_write;
	msg[0].len = sizeof(data_write);
	msg[0].flags = I2C_MSG_WRITE;

	msg[1].buf = (uint8_t *)p_values;
	msg[1].len = size;
	msg[1].flags = I2C_MSG_WRITE | I2C_MSG_STOP;
	
	return i2c_transfer_dt(p_platform->i2c, msg, 2);
}