As already mentioned in this question Reading and writing with smbus package, there are chips that apart for standard SDA and SCL lines use a third communication line. This means that this “modified” I2C communication cannot be made using standard kernel and smbus library, which advantage is that communication is very orderly (perfect SCL pulses).

I already managed to bitbang communication using RPi.GPIO library. The communication works, but it is uneven and each clock pulse has different length, since RPi.GPIO library (and probably Python itself) is just too slow.

Now I want to write my own library for the communication with the chip. In order for library to work properly, I have to solve two problems:

1. Would it be appropriate to use standard I2C Raspberry Pi pins (8, 9) and one arbitrary pin for that? Maybe this is not good idea because it might create a conflict with kernel and smbus library? What do you think?
2. How should I write this communication to be as orderly as possible – should I write special C routines within my Python program and what commands should I use to access the pins?

I would prefer solutions that don’t use other communication libraries (e.g. RPi.GPIO, pigpio)