Drv::LinuxI2cDriver

1. Introduction

The LinuxI2cDriver component provides a Linux-specific implementation of an I2C (Inter-Integrated Circuit) bus master driver. It implements the Drv.I2c interface, exposing guarded synchronous ports for writing to, reading from, and performing combined write/read transactions with I2C slave devices.

The component wraps the Linux userspace I2C device interface (/dev/i2c-*, via ioctl with I2C_RDWR and read/write system calls) to perform bus transactions on behalf of client components.

2. Requirements

3. Design

The LinuxI2cDriver is a passive component. All operations execute synchronously on the caller's thread; the Drv.I2c interface ports are guarded, so concurrent transactions from multiple callers are serialized by the component's mutex.

3.1 Port Description

3.2 Transaction Handling

1. Each handler validates that the device file descriptor is open, returning I2cStatus::I2C_OPEN_ERR otherwise.
2. write and read handlers select the slave address with ioctl(I2C_SLAVE) (failure yields I2C_ADDRESS_ERR) and issue write()/read() system calls sized by the provided Fw::Buffer (failures yield I2C_WRITE_ERR/I2C_READ_ERR).
3. The writeRead handler issues a combined transaction via ioctl(I2C_RDWR), so the write and read occur back-to-back with a repeated start condition. This is required by devices that lose register-pointer state if the bus is released between the address write and the data read. Because the combined transaction reports a single result, failures are reported as I2C_OTHER_ERR.

3.3 Stub Implementation

A stub implementation (LinuxI2cDriverStub.cpp) is provided for platforms without Linux I2C support; it reports open failures for all transactions. The build selects the real or stub implementation based on the target platform.

4. Usage

The typical usage pattern is:

1. Instantiate the component in the topology.
2. Open the device by calling open("/dev/i2c-<N>") from topology setup code before any transactions are performed. open returns false on failure.
3. Perform transactions by invoking the write, read, or writeRead ports with the slave address and data buffer(s).

// Topology configuration example
i2cDriver.open("/dev/i2c-1");

Note that the caller owns the buffers passed to each port; the driver does not retain or deallocate them.

5. Change Log