[uart] Add packet_transport platform (#8214)

Co-authored-by: Faidon Liambotis <paravoid@debian.org>
Co-authored-by: clydeps <U5yx99dok9>
Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

CODEOWNERS

@@ -468,6 +468,7 @@ esphome/components/tuya/switch/* @jesserockz
 esphome/components/tuya/text_sensor/* @dentra
 esphome/components/uart/* @esphome/core
 esphome/components/uart/button/* @ssieb
+esphome/components/uart/packet_transport/* @clydebarrow
 esphome/components/udp/* @clydebarrow
 esphome/components/ufire_ec/* @pvizeli
 esphome/components/ufire_ise/* @pvizeli

esphome/components/uart/packet_transport/__init__.py

@@ -0,0 +1,20 @@
+from esphome.components.packet_transport import (
+    PacketTransport,
+    new_packet_transport,
+    transport_schema,
+)
+from esphome.cpp_types import PollingComponent
+
+from .. import UART_DEVICE_SCHEMA, register_uart_device, uart_ns
+
+CODEOWNERS = ["@clydebarrow"]
+DEPENDENCIES = ["uart"]
+
+UARTTransport = uart_ns.class_("UARTTransport", PacketTransport, PollingComponent)
+
+CONFIG_SCHEMA = transport_schema(UARTTransport).extend(UART_DEVICE_SCHEMA)
+
+
+async def to_code(config):
+    var, _ = await new_packet_transport(config)
+    await register_uart_device(var, config)

esphome/components/uart/packet_transport/uart_transport.cpp

@@ -0,0 +1,88 @@
+#include "esphome/core/log.h"
+#include "esphome/core/application.h"
+#include "uart_transport.h"
+
+namespace esphome {
+namespace uart {
+
+static const char *const TAG = "uart_transport";
+
+void UARTTransport::loop() {
+  PacketTransport::loop();
+
+  while (this->parent_->available()) {
+    uint8_t byte;
+    if (!this->parent_->read_byte(&byte)) {
+      ESP_LOGW(TAG, "Failed to read byte from UART");
+      return;
+    }
+    if (byte == FLAG_BYTE) {
+      if (this->rx_started_ && this->receive_buffer_.size() > 6) {
+        auto len = this->receive_buffer_.size();
+        auto crc = crc16(this->receive_buffer_.data(), len - 2);
+        if (crc != (this->receive_buffer_[len - 2] | (this->receive_buffer_[len - 1] << 8))) {
+          ESP_LOGD(TAG, "CRC mismatch, discarding packet");
+          this->rx_started_ = false;
+          this->receive_buffer_.clear();
+          continue;
+        }
+        this->receive_buffer_.resize(len - 2);
+        this->process_(this->receive_buffer_);
+        this->rx_started_ = false;
+      } else {
+        this->rx_started_ = true;
+      }
+      this->receive_buffer_.clear();
+      this->rx_control_ = false;
+      continue;
+    }
+    if (!this->rx_started_)
+      continue;
+    if (byte == CONTROL_BYTE) {
+      this->rx_control_ = true;
+      continue;
+    }
+    if (this->rx_control_) {
+      byte ^= 0x20;
+      this->rx_control_ = false;
+    }
+    if (this->receive_buffer_.size() == MAX_PACKET_SIZE) {
+      ESP_LOGD(TAG, "Packet too large, discarding");
+      this->rx_started_ = false;
+      this->receive_buffer_.clear();
+      continue;
+    }
+    this->receive_buffer_.push_back(byte);
+  }
+}
+
+void UARTTransport::update() {
+  this->updated_ = true;
+  this->resend_data_ = true;
+  PacketTransport::update();
+}
+
+/**
+ * Write a byte to the UART bus. If the byte is a flag or control byte, it will be escaped.
+ * @param byte The byte to write.
+ */
+void UARTTransport::write_byte_(uint8_t byte) const {
+  if (byte == FLAG_BYTE || byte == CONTROL_BYTE) {
+    this->parent_->write_byte(CONTROL_BYTE);
+    byte ^= 0x20;
+  }
+  this->parent_->write_byte(byte);
+}
+
+void UARTTransport::send_packet(std::vector<uint8_t> &buf) const {
+  this->parent_->write_byte(FLAG_BYTE);
+  for (uint8_t byte : buf) {
+    this->write_byte_(byte);
+  }
+  auto crc = crc16(buf.data(), buf.size());
+  this->write_byte_(crc & 0xFF);
+  this->write_byte_(crc >> 8);
+  this->parent_->write_byte(FLAG_BYTE);
+}
+}  // namespace uart
+}  // namespace esphome

esphome/components/uart/packet_transport/uart_transport.h

@@ -0,0 +1,41 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/packet_transport/packet_transport.h"
+#include <vector>
+#include "../uart.h"
+
+namespace esphome {
+namespace uart {
+
+/**
+ * A transport protocol for sending and receiving packets over a UART connection.
+ * The protocol is based on Asynchronous HDLC framing. (https://en.wikipedia.org/wiki/High-Level_Data_Link_Control)
+ * There are two special bytes: FLAG_BYTE and CONTROL_BYTE.
+ * A 16-bit CRC is appended to the packet, then
+ * the protocol wraps the resulting data between FLAG_BYTEs.
+ * Any occurrence of FLAG_BYTE or CONTROL_BYTE in the data is escaped by emitting CONTROL_BYTE followed by the byte
+ * XORed with 0x20.
+ */
+static const uint16_t MAX_PACKET_SIZE = 508;
+static const uint8_t FLAG_BYTE = 0x7E;
+static const uint8_t CONTROL_BYTE = 0x7D;
+
+class UARTTransport : public packet_transport::PacketTransport, public UARTDevice {
+ public:
+  void loop() override;
+  void update() override;
+  float get_setup_priority() const override { return setup_priority::PROCESSOR; }
+
+ protected:
+  void write_byte_(uint8_t byte) const;
+  void send_packet(std::vector<uint8_t> &buf) const override;
+  bool should_send() override { return true; };
+  size_t get_max_packet_size() override { return MAX_PACKET_SIZE; }
+  std::vector<uint8_t> receive_buffer_{};
+  bool rx_started_{};
+  bool rx_control_{};
+};
+
+}  // namespace uart
+}  // namespace esphome

tests/components/uart/test.esp32-idf.yaml

@@ -13,3 +13,6 @@ uart:
     rx_buffer_size: 512
     parity: EVEN
     stop_bits: 2
+
+packet_transport:
+  - platform: uart