I2C Primitive Sunfction for Python & Pi

Question

Well-versed in C/C++, but new to Python.

I have done a lot of research here and maybe I am missing something, but it seems that Pi/Python does not have primitive functions for I2C, which is sad to be honest. If this is the case, then I don't understand why the foundation would not support bare-bone I2C. There are some work around's for different cases, but they do not solve all, and with some primitive functions, it could.

Here is one case: 16-bit REG_ADDR WRITE, but doesnt solve 16-bit REG_ADDR READ: https://www.raspberrypi.org/forums/viewtopic.php?t=170062

Here is what is not possible:

• A sensor with 16-bit registers, and 16-bit data. I am not talking about the slaver address. I see a ton of threads where people go back and forth on this subject and mix the 2.

• 7-bit/8-bit slave address

• 16-bit register offsets
• 16-bit data in each offset

How can I communicate with such a device? IS it possible?

• As soon as you want to read, all of the read functions, take an 8-bit read address, thus even if you could write the offset address before a read, the read will fail.

read_block_data(SLAVE_ADDR, REG_ADDR, DATA_ARRAY[]) the REG_ADDR is always 8-bits, hence you cannot talk to a 16-bit address part.

Is there a module someone has to just have primitive write and read functions?

• write a byte array: write(SLAVE_ADDR, BYTEARRAY[])
• read a byte array: Array = read(SLAVE_ADDR)

Why is this not available?

Answer 1

You are confusing a number of issues.

The Pi only really supports 7-bit I2C slave addresses. This isn't normally a problem as you hardly ever come across anything other than 7-bit I2C address devices. I never have.

That has nothing to do with whether the device uses 16-bit or 8-bit (or any other number of bits) for internal register addresses or has 8-bit or 16-bit internal storage size. I2C always transfers in units of 8-bit bytes. So to read/write a 16-bit register you transfer two bytes.

The Python SMBus module only supports SMBus commands (with a couple of irrelevant to this answer exceptions). This is okay for most but not all I2C devices.

My pigpio library does offer I2C as well as SMBus support.

The I2C support is for arbitrary length read and write of bytes.

For Python see i2c_read_device and i2c_write_device.

Answer 2

Hi This may be the answer to use PIGPIO, however it is not being found after installations. I followed the directions to download the zip, unzip, make & install. I think I may have an issue with directories.

** using Python v3.5, on a Pi Zero W.

Thanks, -P