Checksum
guilyx opened this issue · 5 comments
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.
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:
- Not all chips support hardware CRC / or it maybe disabled in particular project.
- Using software implementation will increase byte footprint.
- 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)
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!
This is common pattern to interact through I2C bus:
- to perform write operation on remote
i2cdevice set first bit to0(actually just shift left) - to perform read - set it to
1
Alright. Thanks alot.