pw_i2c/docs.rst

.. _module-pw_i2c:

------
pw_i2c
------

.. warning::
  This module is under construction, not ready for use, and the documentation
  is incomplete.

pw_i2c contains interfaces and utility functions for using I2C.

Features
========

pw::i2c::Initiator
------------------
.. inclusive-language: disable

The common interface for initiating transactions with devices on an I2C bus.
Other documentation sources may call this style of interface an I2C "master",
"central" or "controller".

.. inclusive-language: enable

pw::i2c::Device
---------------
The common interface for interfacing with generic I2C devices. This object
contains ``pw::i2c::Address`` and wraps the ``pw::i2c::Initiator`` API.
Common use case includes streaming arbitrary data (Read/Write). Only works
with devices with a single device address.

pw::i2c::RegisterDevice
-----------------------
The common interface for interfacing with register devices. Contains methods
to help read and write registers from and to the device. Users should have a
understanding of the capabilities of their device such as register address
sizes, register data sizes, byte addressability, bulk transactions, etc in
order to effectively use this interface.

pw::i2c::MockInitiator
----------------------
A generic mocked backend for for pw::i2c::Initiator. This is specifically
intended for use when developing drivers for i2c devices. This is structured
around a set of 'transactions' where each transaction contains a write, read and
a timeout. A transaction list can then be passed to the MockInitiator, where
each consecutive call to read/write will iterate to the next transaction in the
list. An example of this is shown below:

.. code-block:: cpp

  using pw::i2c::Address;
  using pw::i2c::MakeExpectedTransactionlist;
  using pw::i2c::MockInitiator;
  using pw::i2c::WriteTransaction;
  using std::literals::chrono_literals::ms;

  constexpr Address kAddress1 = Address::SevenBit<0x01>();
  constexpr auto kExpectWrite1 = pw::bytes::Array<1, 2, 3, 4, 5>();
  constexpr auto kExpectWrite2 = pw::bytes::Array<3, 4, 5>();
  auto expected_transactions = MakeExpectedTransactionArray(
      {WriteTransaction(pw::OkStatus(), kAddress1, kExpectWrite1, 1ms),
       WriteTransaction(pw::OkStatus(), kAddress2, kExpectWrite2, 1ms)});
  MockInitiator i2c_mock(expected_transactions);

  // Begin driver code
  ConstByteSpan write1 = kExpectWrite1;
  // write1 is ok as i2c_mock expects {1, 2, 3, 4, 5} == {1, 2, 3, 4, 5}
  Status status = i2c_mock.WriteFor(kAddress1, write1, 2ms);

  // Takes the first two bytes from the expected array to build a mismatching
  // span to write.
  ConstByteSpan write2 = std::span(kExpectWrite2).first(2);
  // write2 fails as i2c_mock expects {3, 4, 5} != {3, 4}
  status = i2c_mock.WriteFor(kAddress2, write2, 2ms);
  // End driver code

  // Optionally check if the mocked transaction list has been exhausted.
  // Alternatively this is also called from MockInitiator::~MockInitiator().
  EXPECT_EQ(mocked_i2c.Finalize(), OkStatus());

pw::i2c::GmockInitiator
-----------------------
gMock of Initiator used for testing and mocking out the Initiator.