Using a simple Python script, I was controlling the relays quickly. So far, so good.

I plugged a SI7020-A20 (temperature / humidity sensor) into the I2C bus. The LED lights up.

This device has no addressable registers, so has a different programming interface than what the onionI2C Python library provides. There is i2c.readBytes(), but no i2c.read(). I suspect this is the root of my problem, but I tried this Python script:

#!/usr/bin/env python
from OmegaExpansion import onionI2C
import time

i2c = onionI2C.OnionI2C()

i2c.write(0x40, [0xF5]) # 0x40 is the I2C address, 0xF5 is the command to start a conversion
time.sleep(0.5)

data = i2c .readBytes(0x40, 0x00, 2) # This device has no addressable registers, so this readBytes() call is suspect, but there is no i2c .read()

print "%x" %data[0]
print "%x" %data[1]

I get:

0

3f

Specced conversion gives RH of -5.88%. I've never heard of negative humidity!

I'm sure it's something really silly, but I have fiddled around a lot with the write(), writeBytes(), and readBytes() calls and not gotten anywhere.

It could be that I need to abandon Python and try to use more primitive functions that might be available in the C libraries, but I was sorta trying to avoid that. I haven't gotten anywhere with the cloud C compiler at all! All I get is an inert Web page that doesn't do anything.

It looks like the Linux i2c-dev interface should itself be able to do the kinds of raw byte access you want

https://www.kernel.org/doc/Documentation/i2c/dev-interface

That is mostly simple file operations, but you will need to use an ioctl() call to set the target chip's address.

• You get a working cross compiler as a result of a build of the system from source

• There appear to be ways to perform an ioctl() from python, for example there's an "fcntl" module that has this capability, you could see if that or something similar is available.

Update: looks like all the pieces you need are available in python C code in the onion i2c library, you just need to refactor them somewhat.

_i2c_writeBuffer appears to operate without the assumption that the first byte sent is an internal register address, it is then used by higher level functions that do enforce that assumption that is problematic for your case.

I'm not immediately seeing a corresponding raw buffer read, but you should be able to make one from the piece there, perhaps just by making a copy that doesn't do a write to send a register address, but instead goes right to the read.

Needless to say i2c debugging is a lot easier with the aid of a storage scope or a simple USB-based logic analyzer - you can figure it all out from what should be happening but it goes a lot faster when you can see what is happening.

2nd Update: realizing the above is C code, not python that you could use without the cross compiler. But that C code includes the ability to do the necessary ioctl() call, so perhaps you can use the built library to open the i2c device "file", perform the ioctl() call to set the peripheral address, but then do the actual byte writing/reading using file operations on that file descriptor directly from python.

Unfortunately, my code is currently only for the Omega1, it will not work as is for the Omega2. I need to make some changes for the Omega2 - I intend to do this but can't at the moment say when I will have time to do so (paid work getting in the way )

libsoc itself: https://dl.dropboxusercontent.com/u/11811685/omega2-stuff/libsoc_0.8.2-230117-1_mipsel_24kc.ipk
python2-bindings: https://dl.dropboxusercontent.com/u/11811685/omega2-stuff/python-libsoc_0.8.2-230117-1_mipsel_24kc.ipk
python3-bindings: https://dl.dropboxusercontent.com/u/11811685/omega2-stuff/python3-libsoc_0.8.2-230117-1_mipsel_24kc.ipk

EDIT: Thought to add the LEDE-package Makefile for libsoc that I made: https://dl.dropboxusercontent.com/u/11811685/omega2-stuff/lede-libsoc-Makefile -- this is only useful for those who wish to build their own LEDE-packages, so everyone else can just ignore this.

I want to thank everyone for their thoughtful responses.

I'm afraid I have a IoT noob question. How do I go about installing an .ipk file? I'd like to have a go with WereCatf's libsoc. Seems like the path of least resistance.

Thanks!

Art

How do I go about installing an .ipk file?

Download the file, then opkg install package.ipk

Do note that I haven't tested these on the official firmware, so I don't 100% guarantee they work. But they should work just fine.

Installing python-libsoc (0.8.2-230117-1) to root...
Collected errors:

• satisfy_dependencies_for: Cannot satisfy the following dependencies for python-libsoc:

•  pkg-config *    libsoc *
  

• opkg_install_cmd: Cannot install package python-libsoc.

Ouch....

Thanks.
-Casten

Original Arduino Source: https://github.com/SparkysWidgets/MinipHBFW/blob/master/MinipH.ino
Python Version: https://github.com/SparkysWidgets/MinipHBFW/blob/master/RaspberryPi - Python3/pHReader.py

Compiled packages are available on https://www.dropbox.com/sh/p7mki5nbgyu1tcv/AABPC1HzA848MbEA9RpNiNNva?dl=0

One can install them with opkg install libonioni2c_0.4-2_mipsel_24kc.ipk pyOnionI2C_0.4-2_mipsel_24kc.ipk pyOmegaExpansion_0.4-2_mipsel_24kc.ipk liboniondebug_0.4-2_mipsel_24kc.ipk

Example using modified python library: https://gist.github.com/foxel/a163231293d7cf6f24831b363a91dfe5