What does reg[] mean in the twi_sensor example?

[eggmoneyna]

I am a recent student interested in Nordic. I know that my skills are very, very poor. Sorry for asking this question T_T
I want to use i2c sensor vl53l1x. I tried to refer to the SDK's basic example twi_sensor, but I couldn't understand the tx of the temperature sensor lm75b.

What I understand is that according to the data sheet, lm75b is W/R (that is, 3 bytes) and vl53l1x is [address, index1, index0, value] (that is, 4 bytes). W/R.

However, in the datasheet of vl53l1x, only the registers are modelID(0xEA), moduleType(0xCC), and Mask revision(0x11). (I found out through many searches that vl53l1x_address is 0x29.)

Not only can I not understand why uint8_t reg[] in the lm75b example was declared that way, and I don't know how to declare reg[] to test vl53l1x.

Please help ㅠㅠ

[haakonsh]

I suggest you start by studying ST's vl53l1x driver as you should only need to port the R/W functions to the nRFX TWI driver. 

See for instance https://www.st.com/resource/en/user_manual/dm00562924-a-guide-to-using-the-vl53l1x-ultra-lite-driver-stmicroelectronics.pdf 

and https://www.st.com/en/imaging-and-photonics-solutions/vl53l1x.html#documentation. 

[eggmoneyna]

thank you. However, I do not understand the ST driver, so I try to use the Arduino driver. ㅜㅜ

Arduino code:
/*****************************************/
void VL53L1X::writeReg(uint16_t reg, uint8_t value)
{
bus->beginTransmission(address);
bus->write((reg >> 8) & 0xFF); // reg high byte
bus->write(reg & 0xFF); // reg low byte
bus->write(value);
last_status = bus->endTransmission();
}

uint8_t VL53L1X::readReg(regAddr reg)
{
uint8_t value;

bus->beginTransmission(address);
bus->write((reg >> 8) & 0xFF); // reg high byte
bus->write(reg & 0xFF); // reg low byte
last_status = bus->endTransmission();

bus->requestFrom(address, (uint8_t)1);
value = bus->read();

return value;
}
/******************************************/

nRF52 Code:

//void vl53l1x_set_mode()
void writeReg(uint16_t reg, uint8_t value)
{
ret_code_t err_code;

uint16_t tx_data[2];
tx_data[0] = (((reg >> 8)& 0xFF) | reg & 0xFF);
tx_data[1] = value;

err_code = nrf_drv_twi_tx(&m_twi, VL53L1X_ADDR, tx_data, sizeof(tx_data), false);
return err_code;
}

//void read_vl53l1x_data()
uint8_t readReg(uint16_t reg)
{
ret_code_t err_code;
uint16_t read_data[2];
uint16_t read_addr = (((reg >> 8)& 0xFF) | reg & 0xFF);
#if 1
err_code = nrf_drv_twi_tx(&m_twi, VL53L1X_ADDR, &read_addr, 1, false);
if(err_code != NRF_SUCCESS)
{
return err_code;
}
#endif
err_code = nrf_drv_twi_rx(&m_twi, VL53L1X_ADDR, read_data, 1);

return read_data[0];
}
/************************************/

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Is it correct to change arduino wire.h like this? I tried but saw only output 0..

[haakonsh]

You need to read the definition of the readReg function a few times more and try figure out exactly what this function does and why it will never return the content of a TWI transfer's buffer.