Work on python master class

[MkLHX]

Hello, i'm working on python class to permit Raspberry as i2c Master with ESP32 slave. look #2

I have to convert the parcker and unpacker class into python code and i'm facing about this operation => https://github.com/gutierrezps/ESP32_I2C_Slave/blob/1224da32dd54f31ce62016438a25871d8d67324c/src/WirePacker.cpp#L63

What is the goal of >buffer_ + 2< ? bytearray + 2 🤓

Why using packer and unpacker data workflow? is it the esp-idf layer who need this data format?

[gutierrezps]

buffer_ holds the following content (shown on README):

	Start	Length	Data[0]	Data[1]	...	Data[n-1]	CRC8	End
byte index	0	1	2	3	...	n+1	n+2	n+3
value	0x02	n+4	data[0]	data[1]	...	data[n-1]	crc of [1..(n+1)]	0x04

CRC is calculated from buffer_[1] to buffer_[n+1]. So buffer_[1] which holds totalLength is added to the CRC on the previous line

https://github.com/gutierrezps/ESP32_I2C_Slave/blob/1224da32dd54f31ce62016438a25871d8d67324c/src/WirePacker.cpp#L62

and

https://github.com/gutierrezps/ESP32_I2C_Slave/blob/1224da32dd54f31ce62016438a25871d8d67324c/src/WirePacker.cpp#L63

updates the CRC with the contents of data i.e. buffer[2...n+1].

[gutierrezps]

Why using packer and unpacker data workflow?

It's explained here: https://github.com/gutierrezps/ESP32_I2C_Slave#how-it-works

[MkLHX]

@gutierrezps yeah i read and understand everything. but my question is really what is the goal in c++ side to make buffer + 2 operation? buffer is an byte array and wat do the + 2 operation on this array? i cannot understand by my self sorry.

[gutierrezps]

buffer is a pointer to the first byte of the array. buffer + 2 is therefore a pointer to the third byte of the array.

https://www.tutorialspoint.com/cplusplus/cpp_pointer_arithmatic.htm

[MkLHX]

ok thx 👍

[MkLHX]

Hello, here my work to allow raspberry pi to communicate with ESP32 as slave on i2c bus https://github.com/MkLHX/Raspberry_Pi_Master_for_ESP32_I2C_SLAVE

[gutierrezps]

Great! I've added the link to your library on README.md.