Checksum

[guilyx]

Hey,

I'm currently using your Si7021 driver implementation on a STM32F4Discovery and I was wondering why, to measure humidity and temperature, you were using

res = HAL_I2C_Master_Receive(hi2c, SI7021_ADDRESS_READ, si7021_buf, 3, 100);

Why are you reading 3 bytes ? Are you reading the checksum too ? The doc says the checksum is optional, so 2 bytes should work as well right ?

Thanks.

[belyalov]

Hey @Guilyx

Yeah, you're right, 2 bytes should be enough.

I was going to implement checksum verification as well, but, ended up with not to do that because:

1. Not all chips support hardware CRC / or it maybe disabled in particular project.
2. Using software implementation will increase byte footprint.
3. Implementing another function like si7021_measure_temperature_crc(), however, looks like nobody will use it.

So feel free to clean it up :) (or I'll clean it up in the future)

[guilyx]

Hey,

I opened up the merge request. I had another question, saw that on multiple drivers : #define SI7021_ADDRESS_READ (0x40 << 1) | 0x01 #define SI7021_ADDRESS_WRITE (0x40 << 1)

Why do you apply a left offset on the base address ? Thought the read/write command was on the last byte of the device's address, not on the last byte of the 8 bits word ? I'm not sure at all, because everyone made their driver this way, I'm just asking.

Documentation from STM32 I2C says :

To enter Transmitter mode, a master sends the slave address with LSB reset. To enter Receiver mode, a master sends the slave address with LSB set.

Any clue/explanations on that please ?

Thanks, I appreciate it!

[belyalov]

This is common pattern to interact through I2C bus:

• to perform write operation on remote i2c device set first bit to 0 (actually just shift left)
• to perform read - set it to 1

[guilyx]

Alright. Thanks alot.

[belyalov]

Fixed by #2