References

This page collects the authoritative technical documents, Linux kernel sources, and related tools that underpin smbus2. They are useful background reading when you need to understand what happens at the protocol or kernel level.

SMBus and I²C Specifications

Resource	Description
SMBus specification archive at smbus.org	Index of all published SMBus specification revisions.
UM10204 — I²C-bus specification and user manual, Rev. 7.0 (2021)	The authoritative NXP/Philips I²C specification. Defines the physical layer, START/STOP conditions, repeated-start, clock stretching, 7-bit and 10-bit addressing, and multi-master arbitration.

Linux Kernel I2C / SMBus Documentation

Document	Description
Linux I2C subsystem documentation	Top-level index for the Linux kernel’s Documentation/i2c/ tree, covering the I2C subsystem from both a device-driver and user-space perspective.
Implementing I2C device drivers in user-space	Describes /dev/i2c-N, the ioctl interface (I2C_RDWR, I2C_SMBUS, I2C_FUNCS, I2C_SLAVE, I2C_SLAVE_FORCE, I2C_PEC, I2C_TENBIT), and how user-space programs should use them — this is the exact interface smbus2 wraps.
SMBus protocol summary in the kernel docs	Kernel-side summary of every SMBus transaction type and the corresponding ioctl arguments used by the in-kernel SMBus layer.
Fault codes returned by the I2C/SMBus layer	Documents the errno values that the kernel I2C subsystem can return — helpful when interpreting OSError exceptions raised by smbus2.
I2C / SMBus Functionality Flags	Explains the I2C_FUNCS flags (read via bus.funcs / I2cFunc in smbus2) and which flags correspond to which operations.
10-bit I2C addressing	Background on 10-bit address support in the Linux I2C subsystem (I2C_FUNC_10BIT_ADDR).
Instantiating I2C devices	How the kernel binds drivers to I2C devices — relevant when a device is already claimed by a kernel driver and you receive EBUSY.

Linux Kernel Header Files

These C headers define the data structures and constants that smbus2 mirrors via ctypes. They ship with the Linux kernel source tree and are also available in most distributions’ linux-headers-* or kernel-headers packages.

Header	Relevance
include/uapi/linux/i2c.h	Defines struct i2c_msg, I2C_M_* message flags, and struct i2c_rdwr_ioctl_data — the data structure passed to I2C_RDWR.
include/uapi/linux/i2c-dev.h	Defines all ioctl request codes for /dev/i2c-N: I2C_SLAVE, I2C_SLAVE_FORCE, I2C_TENBIT, I2C_FUNCS, I2C_RDWR, I2C_PEC, I2C_SMBUS; also defines struct i2c_smbus_ioctl_data and union i2c_smbus_data.
include/uapi/linux/i2c-smbus.h	Defines I2C_SMBUS_* transaction-type constants (I2C_SMBUS_BYTE, I2C_SMBUS_BYTE_DATA, I2C_SMBUS_WORD_DATA, I2C_SMBUS_BLOCK_DATA, I2C_SMBUS_I2C_BLOCK_DATA, I2C_SMBUS_PROC_CALL, etc.) that correspond to each smbus2 method.

i2c-tools User-Space Utilities

The i2c-tools package provides the command-line utilities commonly used alongside smbus2 for bus discovery and manual device interrogation.

Tool / Resource	Description
i2c-tools project page (kernel.org)	Home page for the i2c-tools package.
i2c-tools source repository	Source for i2cdetect, i2cdump, i2cget, i2cset, and i2ctransfer.
i2cdetect -y 1	Scan bus 1 for responding device addresses — the first diagnostic step when a device is not found.
i2cdump -y 1 0x50	Dump all registers of the device at address 0x50 on bus 1.
i2ctransfer -y 1 w1@0x50 0x00 r2@0x50	Perform a write-then-read transaction (equivalent to smbus2’s i2c_rdwr with two messages).

Python ctypes and struct References

smbus2 uses ctypes internally to construct kernel data structures. The tips in the documentation (e.g. signed-integer conversion, endianness swap) also use standard-library modules.

Reference	Description
Python ctypes documentation	Python’s foreign-function and C-compatible type library — used by smbus2 for ioctl buffer layout and by users for signed-integer conversion.
Python struct documentation	Pack/unpack bytes with format strings — useful for byte-order conversion of multi-byte sensor values.
Python fcntl documentation	The Linux-only standard-library module that smbus2 uses to issue ioctl system calls.

smbus2 Project Resources

Resource	URL
GitHub repository	https://github.com/kplindegaard/smbus2
PyPI package	https://pypi.org/project/smbus2/
Read the Docs (API docs)	https://smbus2.readthedocs.io/en/latest/
Changelog	CHANGELOG.md
Issue tracker	https://github.com/kplindegaard/smbus2/issues