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// Copyright 2020 The Pigweed Authors
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#pragma once
#include <array>
#include "pw_assert/assert.h"
#include "pw_hdlc/encoded_size.h"
#include "pw_hdlc/encoder.h"
#include "pw_rpc/channel.h"
#include "pw_span/span.h"
#include "pw_stream/stream.h"
namespace pw::hdlc {
// Custom HDLC ChannelOutput class to write and read data through serial using
// the HDLC protocol.
// WARNING: This ChannelOutput is not thread-safe. If thread-safety is required,
// create a similar class that adds a mtuex to Send.
class RpcChannelOutput : public rpc::ChannelOutput {
// The RpcChannelOutput class does not own the buffer it uses to store the
// protobuf bytes. This buffer is specified at the time of creation along with
// a writer object to which will be used to write and send the bytes.
constexpr RpcChannelOutput(stream::Writer& writer,
uint64_t address,
const char* channel_name)
: ChannelOutput(channel_name), writer_(writer), address_(address) {}
Status Send(span<const std::byte> buffer) override {
return hdlc::WriteUIFrame(address_, buffer, writer_);
stream::Writer& writer_;
const uint64_t address_;
// A RpcChannelOutput that ensures all packets produced by pw_rpc will safely
// fit in the specified MTU after HDLC encoding.
template <size_t kMaxTransmissionUnit>
class FixedMtuChannelOutput : public RpcChannelOutput {
constexpr FixedMtuChannelOutput(stream::Writer& writer,
uint64_t address,
const char* channel_name)
: RpcChannelOutput(writer, address, channel_name) {}
// Provide a constexpr helper for the maximum safe payload size.
static constexpr size_t MaxSafePayloadSize() {
static_assert(rpc::cfg::kEncodingBufferSizeBytes <=
"pw_rpc's encode buffer is large enough to produce HDLC "
"frames that will exceed the bounds of this channel's MTU");
hdlc::MaxSafePayloadSize(kMaxTransmissionUnit)) > 0,
"The combined MTU and RPC encode buffer size do not afford enough "
"space for any RPC payload data to safely be encoded into RPC packets");
return rpc::MaxSafePayloadSize(
// Users of pw_rpc should only care about the maximum payload size, despite
// this being labeled as a MTU.
size_t MaximumTransmissionUnit() override { return MaxSafePayloadSize(); }
} // namespace pw::hdlc