sdk/fidl/fuchsia.hardware.i2c/i2c.fidl

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

library fuchsia.hardware.i2c;

using zx;

const uint32 MAX_TRANSFER_SIZE = 8196; // More than enough for I2C
const uint32 MAX_COUNT_SEGMENTS = 8; // Enough for all known transfer configurations.

enum SegmentType {
    /// Flags the end of a serialized list of segments.
    END = 1;
    /// Segment to be read from the I2C device.
    READ = 2;
    /// Segment to be written to the I2C device.
    WRITE = 3;
};

/// Segment header for a serialized SubordinateTransfer.
/// TODO(ZX-3029): Avoid requiring serialization and have SubordinateTransfer take an argument of
/// `vector<Segment>:MAX_SEGMENTS` instead once we have better support in the C bindings or for C++.
struct Segment {
    uint32 type;
    uint32 len;
};

[Layout = "Simple"]
protocol Device {
    /// Send and receive data on the I2C device.
    SubordinateTransfer(vector<uint8>:MAX_TRANSFER_SIZE in) -> (zx.status s,
                                                                vector<uint8>:MAX_TRANSFER_SIZE out);
};

// |Device2| removes the simple layout restriction and fully specifies the format in FIDL instead
// of manually parsed structs as |Device| above.
protocol Device2 {
    /// Write and read segments of data for a particular I2C device.
    ///
    /// The |segments_is_write| vector specifies the type (write or read) of each segment.
    /// The |write_segments_data| vector of segments specifies the data to write for each write
    /// segment. Each segment itself is a vector of uint8s, so |write_segments_data| is a vector of
    /// vectors of uint8s.
    /// The |read_segments_length| vector specifies the length of the read segments.
    /// If there is no error, |read_segments_data| returns a vector of segments, with each segment
    /// data itself returned in vectors.
    ///
    /// For a simple I2C read, for instance 2 bytes write followed by one byte read,
    /// |segments_is_write| would be a vector with 2 elements: true, false and
    /// |write_segments_data| would be a vector with 1 element including the 2 bytes address of the
    /// read. Upon success |read_segments_data| would return a vector with one element, the byte
    /// read.
    Transfer(vector<bool>:MAX_COUNT_SEGMENTS segments_is_write,
             vector<vector<uint8>:MAX_TRANSFER_SIZE>:MAX_COUNT_SEGMENTS write_segments_data,
             vector<uint8>:MAX_COUNT_SEGMENTS read_segments_length)
        -> (vector<vector<uint8>:MAX_TRANSFER_SIZE>:MAX_COUNT_SEGMENTS read_segments_data)
        error zx.status;
};