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esphome/esphome/components/modbus/modbus.cpp
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#include "modbus.h"
#include "esphome/core/application.h"
#include "esphome/core/helpers.h"
#include "esphome/core/log.h"
namespace esphome::modbus {
static const char *const TAG = "modbus";
// Maximum bytes to log for Modbus frames (truncated if larger)
static constexpr size_t MODBUS_MAX_LOG_BYTES = 64;
// Approximate bits per character on the wire (depends on parity/stop bit config)
static constexpr uint32_t MODBUS_BITS_PER_CHAR = 11;
// Milliseconds per second
static constexpr uint32_t MS_PER_SEC = 1000;
void Modbus::setup() {
if (this->flow_control_pin_ != nullptr) {
this->flow_control_pin_->setup();
}
this->frame_delay_ms_ =
std::max(2, // 1750us minimum per spec - rounded up to 2ms.
// 3.5 characters * 11 bits per character * 1000ms/sec / (bits/sec) (Standard modbus frame delay)
(uint16_t) (3.5 * MODBUS_BITS_PER_CHAR * MS_PER_SEC / this->parent_->get_baud_rate()) + 1);
// When rx_full_threshold is configured (non-zero), the UART has a hardware FIFO with a
// meaningful threshold (e.g., ESP32 native UART), so we can calculate a precise delay.
// Otherwise (e.g., USB UART), use 50ms to handle data arriving in chunks.
static constexpr uint16_t DEFAULT_LONG_RX_BUFFER_DELAY_MS = 50;
size_t rx_threshold = this->parent_->get_rx_full_threshold();
this->long_rx_buffer_delay_ms_ =
rx_threshold != uart::UARTComponent::RX_FULL_THRESHOLD_UNSET
? (rx_threshold * MODBUS_BITS_PER_CHAR * MS_PER_SEC / this->parent_->get_baud_rate()) + 1
: DEFAULT_LONG_RX_BUFFER_DELAY_MS;
}
void Modbus::loop() {
// Receive any available bytes from UART
this->receive_bytes_();
// Parse bytes into frames and process them
this->parse_modbus_frames();
}
void ModbusClientHub::loop() {
// Call base class to receive bytes and parse frames
this->Modbus::loop();
// If we're past the send_wait_time timeout and response buffer doesn't have the start of the expected response
if (this->waiting_for_response_.has_value()) {
ModbusDeviceCommand &wfr = this->waiting_for_response_.value();
uint8_t expected_address = wfr.frame.address();
if (this->last_receive_check_ - this->last_send_ > this->last_send_tx_offset_ + this->send_wait_time_ &&
(this->rx_buffer_.empty() || this->rx_buffer_[0] != expected_address)) {
ESP_LOGW(TAG, "Stop waiting for response from %" PRIu8 " %" PRIu32 "ms after last send", expected_address,
this->last_receive_check_ - this->last_send_);
this->notify_no_response_(wfr);
this->waiting_for_response_.reset();
}
}
// If there's no response pending and there's commands in the buffer
this->send_next_frame_();
}
bool Modbus::timeout_() {
// If the response frame is finished (including interframe delay) - we timeout.
// The long_rx_buffer_delay accounts for long responses (larger than the UART rx_full_threshold) to avoid timeouts
// when the buffer is filling the back half of the response
const uint16_t timeout = std::max(
(uint16_t) this->frame_delay_ms_,
(uint16_t) (this->rx_buffer_.size() >= this->parent_->get_rx_full_threshold() ? this->long_rx_buffer_delay_ms_
: 0));
return this->last_receive_check_ - this->last_modbus_byte_ > timeout;
}
int32_t Modbus::tx_delay_remaining() {
// We use millis() here and elsewhere instead of App.get_loop_component_start_time() to avoid stale timestamps
// It's critical in all timestamp comparisons that the left timestamp comes before the right one in time
// If we use a cached value in place of millis() and last_modbus_byte_ is updated inside our loop
// then the comparison is backwards (small negative which wraps to large positive) and will cause a false timeout
// So in this component we don't use any cached timestamp values to avoid these annoying bugs
const uint32_t now = millis();
return std::max({(int32_t) 0,
(int32_t) (this->last_send_tx_offset_ + this->frame_delay_ms_ - (now - this->last_send_)),
(int32_t) (this->frame_delay_ms_ - (now - this->last_modbus_byte_))});
}
int32_t ModbusClientHub::tx_delay_remaining() {
const uint32_t now = millis();
return std::max({(int32_t) 0,
(int32_t) (this->last_send_tx_offset_ + this->frame_delay_ms_ + this->turnaround_delay_ms_ -
(now - this->last_send_)),
(int32_t) (this->frame_delay_ms_ + this->turnaround_delay_ms_ - (now - this->last_modbus_byte_))});
}
bool Modbus::tx_blocked() {
// We block transmission in any of these cases:
// 1. There are bytes in the UART Rx buffer
// 2. There are bytes in our Rx buffer
// 3. The last sent byte isn't more than tx_delay ms ago (i.e. wait to tell receivers that our previous Tx is done)
// 4. The last received byte isn't more than tx_delay ms ago (i.e. wait to be sure there isn't more Rx coming)
// N.B. We allow a small delay (MODBUS_TX_MAX_DELAY_MS) to avoid looping on small delays. This gets handled by
// send_frame_.
return this->available() || !this->rx_buffer_.empty() || this->tx_delay_remaining() > MODBUS_TX_MAX_DELAY_MS;
}
bool ModbusClientHub::tx_blocked() {
// We block transmission in any of these case:
// 1. We're waiting for a response
// 2. Any of the base class tx_blocked conditions
return (this->waiting_for_response_.has_value()) || this->Modbus::tx_blocked();
}
bool ModbusClientHub::tx_buffer_empty() { return this->tx_buffer_.empty(); }
void Modbus::receive_bytes_() {
this->last_receive_check_ = millis();
size_t bytes = this->available();
if (bytes) {
size_t buffer_size = this->rx_buffer_.size();
this->last_modbus_byte_ = this->last_receive_check_;
this->rx_buffer_.resize(buffer_size + bytes);
if (!this->read_array(this->rx_buffer_.data() + buffer_size, bytes)) {
this->rx_buffer_.resize(buffer_size);
return;
}
if (buffer_size == 0) {
ESP_LOGV(TAG, "Received first byte %" PRIu8 " (0X%x) of %zu bytes %" PRIu32 "ms after last send",
this->rx_buffer_[0], this->rx_buffer_[0], this->rx_buffer_.size(), millis() - this->last_send_);
}
}
}
void ModbusClientHub::parse_modbus_frames() {
if (!this->rx_buffer_.empty()) {
size_t size;
do {
size = this->rx_buffer_.size();
if (!this->parse_modbus_server_frame_())
this->clear_rx_buffer_(LOG_STR("parse failed"), true);
} while (!this->rx_buffer_.empty() && size > this->rx_buffer_.size());
if (this->timeout_())
this->clear_rx_buffer_(LOG_STR("timeout after partial response"), true);
}
}
void ModbusServerHub::parse_modbus_frames() {
while (!this->rx_buffer_.empty()) {
size_t size = this->rx_buffer_.size();
ESP_LOGVV(TAG, "Parsing frames buffer size = %" PRIu32, size);
bool retry_as_client = false;
if (this->expecting_peer_response_ != 0) {
if (!this->parse_modbus_server_frame_()) {
ESP_LOGV(TAG, "Stop expecting peer response from %" PRIu8 " due to parse failure, and retry parse",
this->expecting_peer_response_);
this->expecting_peer_response_ = 0;
retry_as_client = true;
} else if (this->timeout_() && size == this->rx_buffer_.size()) {
// If we timed out and the above parse attempt did not consume data, stop expecting a response
ESP_LOGV(TAG,
"Stop expecting peer response from %" PRIu8 " due to timeout after partial response, and retry parse",
this->expecting_peer_response_);
this->expecting_peer_response_ = 0;
retry_as_client = true;
}
} else {
if (!this->parse_modbus_client_frame_())
this->clear_rx_buffer_(LOG_STR("parse failed"), true);
}
// Stop if the buffer didn't shrink (no frame consumed) and no mode switch triggered a retry
if (!retry_as_client && size <= this->rx_buffer_.size())
break;
}
if (this->timeout_())
this->clear_rx_buffer_(LOG_STR("timeout after partial response"), true);
}
uint16_t Modbus::find_custom_frame_end_(uint16_t min_length) const {
// Custom functions could be any length - we have to rely on the CRC to determine completeness.
// If a CRC match is never found, the buffer will eventually overflow and be cleared.
const uint8_t *raw = &this->rx_buffer_[0];
const size_t size = this->rx_buffer_.size();
for (uint16_t len = min_length; len <= std::min(size, size_t(MAX_FRAME_SIZE)); len++) {
if (crc16(raw, len) == 0)
return len;
}
return 0;
}
bool Modbus::parse_modbus_server_frame_() {
size_t size = this->rx_buffer_.size();
uint16_t frame_length = helpers::server_frame_length(this->rx_buffer_.data(), this->rx_buffer_.size());
if (size < frame_length)
return true;
uint8_t address = this->rx_buffer_[0];
uint8_t function_code = this->rx_buffer_[1];
if (helpers::is_function_code_custom(function_code)) {
frame_length = this->find_custom_frame_end_(frame_length);
if (frame_length == 0)
return size < MAX_FRAME_SIZE; // Continue to parse until we hit max size
ESP_LOGD(TAG, "User-defined function %02X found", function_code);
} else {
if (crc16(&this->rx_buffer_[0], frame_length) != 0)
return false;
}
// Process before clearing: process_modbus_server_frame (receiving a response or peer message) never sends a reply
// synchronously. We can safely point directly into rx_buffer_ and avoid a copy.
// The PDU is the frame without the leading address and the trailing CRC.
std::span<const uint8_t> pdu(this->rx_buffer_.data() + 1, frame_length - 3);
this->process_modbus_server_frame(address, pdu);
this->clear_rx_buffer_(LOG_STR("parse succeeded"), false, frame_length);
return true;
}
bool ModbusServerHub::parse_modbus_client_frame_() {
size_t size = this->rx_buffer_.size();
uint16_t frame_length = helpers::client_frame_length(this->rx_buffer_.data(), this->rx_buffer_.size());
if (size < frame_length)
return true;
uint8_t address = this->rx_buffer_[0];
uint8_t function_code = this->rx_buffer_[1];
if (helpers::is_function_code_custom(function_code)) {
frame_length = this->find_custom_frame_end_(frame_length);
if (frame_length == 0)
return size < MAX_FRAME_SIZE; // Continue to parse until we hit max size
ESP_LOGD(TAG, "User-defined function %02X found", function_code);
} else {
if (crc16(&this->rx_buffer_[0], frame_length) != 0)
return false;
}
// Clear before processing: process_modbus_client_frame_ dispatches to a server device which sends
// a response immediately. We need to clear the rx buffer first so the response doesn't snag tx_blocked.
// This requires copying the frame data to a local buffer beforehand.
uint8_t data_offset = helpers::client_frame_data_offset(this->rx_buffer_.data(), this->rx_buffer_.size());
uint16_t data_len = frame_length - 2 - data_offset;
uint8_t data[MAX_FRAME_SIZE] = {};
std::memcpy(data, this->rx_buffer_.data() + data_offset, data_len);
this->clear_rx_buffer_(LOG_STR("parse succeeded"), false, frame_length);
this->process_modbus_client_frame_(address, function_code, data);
return true;
}
// Bounds contract, enforced by the parser (parse_modbus_server_frame_) rather than locally:
// - pdu is never empty: helpers::server_pdu_length() returns at least MIN_PDU_SIZE (1) on every
// branch, and find_custom_frame_end_() only ever lengthens the frame, so the PDU always holds
// at least the function code.
// - When the exception bit is set, pdu has at least 2 bytes: server_pdu_length() checks the
// exception bit before anything else and pins those PDUs to 2 bytes, so the exception code
// read below is always present.
// Keep those guarantees in mind when changing server_pdu_length() or adding callers.
void ModbusClientHub::process_modbus_server_frame(uint8_t address, std::span<const uint8_t> pdu) {
const uint8_t function_code = pdu[0];
if (!this->waiting_for_response_.has_value()) {
ESP_LOGW(TAG,
"Received unexpected frame from address %" PRIu8 ", function code 0x%X, %" PRIu32 "ms after last send",
address, function_code, this->last_modbus_byte_ - this->last_send_);
return;
} else { // We are waiting for a response
// Check if the response matches the expected address and function code
ModbusDeviceCommand &wfr = this->waiting_for_response_.value();
uint8_t expected_address = wfr.frame.address();
uint8_t expected_function_code = wfr.frame.pdu()[0];
if (expected_address != address || expected_function_code != (function_code & FUNCTION_CODE_MASK)) {
ESP_LOGW(TAG,
"Received incorrect frame address %" PRIu8 " <> %" PRIu8 " or function code 0x%X <> 0x%X, %" PRIu32
"ms after last send",
address, expected_address, (function_code & FUNCTION_CODE_MASK), expected_function_code,
this->last_modbus_byte_ - this->last_send_);
// Invalidate the device; the entry survives as an interrupted shell so the late response is ignored.
// A retry requested here stays queued behind the shell until the send-wait timeout clears it.
this->notify_no_response_(wfr);
wfr.interrupted = true;
return;
}
if (wfr.interrupted) {
ESP_LOGW(TAG,
"Ignoring response from %" PRIu8 " - transmission interrupted by previous unexpected response, %" PRIu32
"ms after last send",
address, this->last_modbus_byte_ - this->last_send_);
return;
} else { // We have a valid device waiting for this response
// Move the command out of the waiting slot so the request PDU stays alive for the callback.
ModbusDeviceCommand command = std::move(this->waiting_for_response_.value());
this->waiting_for_response_.reset();
ModbusClientDevice *device = command.device;
// The request PDU is the sent frame without the leading address and the trailing CRC.
std::span<const uint8_t> request_pdu = command.frame.pdu();
// Is it an error response?
if (helpers::is_function_code_exception(function_code)) {
uint8_t exception = pdu[1]; // exception frames are fixed-length, so the code is always present
ESP_LOGW(TAG,
"Error function code: 0x%X exception: %" PRIu8 ", address: %" PRIu8 ", %" PRIu32 "ms after last send",
function_code, exception, address, this->last_modbus_byte_ - this->last_send_);
if (device)
device->on_error(request_pdu, static_cast<ExceptionCode>(exception));
} else if (device) { // Not an error response
device->on_response(request_pdu, pdu);
} else { // Not an error response, but no device to respond to
ESP_LOGV(TAG, "Ignoring response from %" PRIu8 " - no callback device set, %" PRIu32 "ms after last send",
address, this->last_modbus_byte_ - this->last_send_);
}
}
}
}
void ModbusServerHub::process_modbus_server_frame(uint8_t address, std::span<const uint8_t>) {
if (this->find_device_(address) != nullptr) {
ESP_LOGE(TAG, "Unexpected response from address %" PRIu8 ", which is mapped to this device.", address);
}
if (this->expecting_peer_response_ == address) {
ESP_LOGV(TAG, "Expected response from peer %" PRIu8 " received", address);
} else {
ESP_LOGV(TAG, "Unexpected response from peer %" PRIu8 " received", address);
}
// This always resets, even if the address doesn't match.
// If an unexpected response is received, we can't trust that a correct response will follow (it shouldn't).
this->expecting_peer_response_ = 0;
}
ModbusServerDevice *ModbusServerHub::find_device_(uint8_t address) {
for (auto *device : this->devices_) {
if (device->get_address() == address) {
return device;
}
}
return nullptr;
}
bool ModbusServerHub::check_register_range_(uint8_t address, uint8_t function_code, uint16_t start_address,
uint16_t number_of_registers) {
if ((uint32_t) start_address + number_of_registers > 0x10000u) {
ESP_LOGW(TAG, "Register address out of range - start: %" PRIu16 " num: %" PRIu16, start_address,
number_of_registers);
this->send_exception_(address, function_code, ExceptionCode::ILLEGAL_DATA_ADDRESS);
return false;
}
return true;
}
void ModbusServerHub::process_modbus_client_frame_(uint8_t address, uint8_t function_code, const uint8_t *data) {
ModbusServerDevice *device = this->find_device_(address);
if (device == nullptr) {
this->expecting_peer_response_ = address;
ESP_LOGV(TAG, "Request to peer %" PRIu8 " received", address);
return;
}
ResponseStatus status;
uint8_t response_buffer[modbus::MAX_RAW_SIZE];
const uint8_t *response_data = response_buffer;
uint16_t response_len = 0;
switch (static_cast<FunctionCode>(function_code)) {
case FunctionCode::READ_HOLDING_REGISTERS:
case FunctionCode::READ_INPUT_REGISTERS: {
// PDU data: start address(2) + quantity(2).
uint16_t start_address = helpers::get_data<uint16_t>(data, 0);
uint16_t number_of_registers = helpers::get_data<uint16_t>(data, 2);
if (number_of_registers == 0 || number_of_registers > MAX_NUM_OF_REGISTERS_TO_READ) {
ESP_LOGW(TAG, "Invalid number of registers %" PRIu16, number_of_registers);
this->send_exception_(address, function_code, ExceptionCode::ILLEGAL_DATA_VALUE);
return;
}
if (!this->check_register_range_(address, function_code, start_address, number_of_registers)) {
return;
}
RegisterValues registers;
if (static_cast<FunctionCode>(function_code) == FunctionCode::READ_HOLDING_REGISTERS) {
status = device->on_read_holding_registers(start_address, number_of_registers, registers);
} else {
status = device->on_read_input_registers(start_address, number_of_registers, registers);
}
// A handler that returns an exception leaves registers partially filled, so check the exception
// first and forward it before validating the register count on the success path.
if (status.has_value()) {
this->send_exception_(address, function_code, status.value());
return;
}
if (registers.size() != number_of_registers) {
ESP_LOGE(TAG, "Incorrect response %" PRIu16 " requested, %zu returned", number_of_registers, registers.size());
this->send_exception_(address, function_code, ExceptionCode::SERVICE_DEVICE_FAILURE);
return;
}
response_buffer[response_len++] = static_cast<uint8_t>(number_of_registers * 2); // actual byte count
for (auto r : registers) {
auto register_bytes = decode_value(r);
response_buffer[response_len++] = register_bytes[0];
response_buffer[response_len++] = register_bytes[1];
}
break;
}
case FunctionCode::WRITE_SINGLE_REGISTER:
case FunctionCode::WRITE_MULTIPLE_REGISTERS: {
// PDU data: start address(2) [+ quantity(2) + byte count(1)] + register values.
// A single-register write always targets one register; for a multiple-register write the
// quantity is in the frame and its byte count must equal quantity * 2. The register values are
// assembled into registers below so the handler doesn't have to know the request framing.
uint16_t start_address = helpers::get_data<uint16_t>(data, 0);
uint16_t number_of_registers = 1;
uint16_t values_offset = 2; // single write: values follow the 2-byte start address
if (static_cast<FunctionCode>(function_code) == FunctionCode::WRITE_MULTIPLE_REGISTERS) {
number_of_registers = helpers::get_data<uint16_t>(data, 2);
uint8_t number_of_bytes = helpers::get_data<uint8_t>(data, 4);
values_offset = 5; // multiple write: values follow start address(2) + quantity(2) + byte count(1)
if (number_of_registers == 0 || number_of_registers > MAX_NUM_OF_REGISTERS_TO_WRITE ||
number_of_registers * 2 != number_of_bytes) {
ESP_LOGW(TAG, "Invalid number of registers %" PRIu16 " or bytes %" PRIu8, number_of_registers,
number_of_bytes);
this->send_exception_(address, function_code, ExceptionCode::ILLEGAL_DATA_VALUE);
return;
}
if (!this->check_register_range_(address, function_code, start_address, number_of_registers)) {
return;
}
}
// Assemble the register values (host byte order) so the handler never sees wire framing.
RegisterValues registers;
for (uint16_t i = 0; i < number_of_registers; i++) {
registers.push_back(helpers::get_data<uint16_t>(data, values_offset + i * 2));
}
status = device->on_write_registers(start_address, registers);
response_data = data; // echo the request header per Modbus 6.6, 6.12
response_len = 4;
break;
}
default:
ESP_LOGW(TAG, "Unsupported function code %" PRIu8, function_code);
this->send_exception_(address, function_code, ExceptionCode::ILLEGAL_FUNCTION);
return;
}
if (status.has_value()) {
this->send_exception_(address, function_code, status.value());
} else {
this->send_response_(address, function_code, response_data, response_len);
}
}
bool Modbus::send_frame_(const ModbusFrame &frame) {
if (this->tx_blocked()) {
ESP_LOGE(TAG, "Attempted to send while transmission blocked");
return false;
}
if (frame.size() > MAX_FRAME_SIZE) {
ESP_LOGE(TAG, "Attempted to send frame larger than max frame size of %" PRIu16 " bytes", MAX_FRAME_SIZE);
return false;
}
const int32_t tx_delay_remaining = this->tx_delay_remaining();
if (tx_delay_remaining > 0) {
delay(tx_delay_remaining);
}
if (this->flow_control_pin_ != nullptr) {
this->flow_control_pin_->digital_write(true);
this->write_array(frame.data.data(), frame.size());
this->flush();
this->flow_control_pin_->digital_write(false);
this->last_send_tx_offset_ = 0;
} else {
this->write_array(frame.data.data(), frame.size());
this->last_send_tx_offset_ = frame.size() * MODBUS_BITS_PER_CHAR * MS_PER_SEC / this->parent_->get_baud_rate() + 1;
}
uint32_t now = millis();
#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
char hex_buf[format_hex_pretty_size(MODBUS_MAX_LOG_BYTES)];
#endif
ESP_LOGV(TAG, "Write: %s %" PRIu32 "ms after last send, %" PRIu32 "ms after last receive",
format_hex_pretty_to(hex_buf, frame.data.data(), frame.size()), now - this->last_send_,
now - this->last_modbus_byte_);
this->last_send_ = now;
return true;
}
void ModbusClientHub::send_next_frame_() {
if (this->tx_buffer_.empty()) {
return;
}
if (this->tx_blocked()) {
return;
}
ModbusDeviceCommand &command = this->tx_buffer_.front();
if (this->send_frame_(command.frame)) {
this->waiting_for_response_ = std::move(command);
} else {
if (command.device)
command.device->on_not_sent();
}
this->tx_buffer_.pop_front();
if (!this->tx_buffer_.empty()) {
ESP_LOGV(TAG, "Write queue contains %zu items.", this->tx_buffer_.size());
}
}
void ModbusClientHub::dump_config() {
ESP_LOGCONFIG(TAG,
"Modbus:\n"
" Send Wait Time: %" PRIu16 " ms\n"
" Turnaround Time: %" PRIu16 " ms\n"
" Frame Delay: %" PRIu16 " ms\n"
" Long Rx Buffer Delay: %" PRIu16 " ms",
this->send_wait_time_, this->turnaround_delay_ms_, this->frame_delay_ms_,
this->long_rx_buffer_delay_ms_);
LOG_PIN(" Flow Control Pin: ", this->flow_control_pin_);
}
void ModbusServerHub::dump_config() {
ESP_LOGCONFIG(TAG,
"Modbus:\n"
" Frame Delay: %" PRIu16 " ms\n"
" Long Rx Buffer Delay: %" PRIu16 " ms",
this->frame_delay_ms_, this->long_rx_buffer_delay_ms_);
LOG_PIN(" Flow Control Pin: ", this->flow_control_pin_);
}
float Modbus::get_setup_priority() const {
// After UART bus
return setup_priority::BUS - 1.0f;
}
void ModbusServerHub::send_response_(uint8_t address, uint8_t function_code, const uint8_t *payload,
uint16_t payload_len) {
// Build the raw frame (address + function code + payload) in a stack buffer; it's consumed
// immediately by send_raw_ and a full raw frame never exceeds MAX_RAW_SIZE.
if (payload_len + 2 > MAX_RAW_SIZE) {
ESP_LOGE(TAG, "Server response too large (%" PRIu16 " bytes)", static_cast<uint16_t>(payload_len + 2));
return;
}
uint8_t raw_frame[MAX_RAW_SIZE];
raw_frame[0] = address;
raw_frame[1] = function_code;
std::memcpy(raw_frame + 2, payload, payload_len);
this->send_raw_(raw_frame, payload_len + 2);
}
void ModbusServerHub::send_exception_(uint8_t address, uint8_t function_code, ExceptionCode exception_code) {
uint8_t raw_frame[3];
raw_frame[0] = address;
raw_frame[1] = function_code | FUNCTION_CODE_EXCEPTION_MASK;
raw_frame[2] = static_cast<uint8_t>(exception_code);
this->send_raw_(raw_frame, 3);
}
void ModbusClientHub::notify_no_response_(ModbusDeviceCommand &wfr) {
if (wfr.device == nullptr)
return;
const bool retry = wfr.device->on_no_response();
// The callback may have detached the device (e.g. clear_tx_queue_for_device()); honor the detach
// over the retry request rather than re-queueing a frame that can no longer be routed.
if (retry && wfr.device != nullptr)
this->requeue_waiting_frame_(wfr);
// The old transaction is over either way; never deliver anything else to the device through it.
wfr.device = nullptr;
}
void ModbusClientHub::requeue_waiting_frame_(ModbusDeviceCommand &wfr) {
const ModbusFrame &frame = wfr.frame;
if (this->tx_buffer_.size() >= MODBUS_TX_BUFFER_SIZE) {
ESP_LOGE(TAG, "Write buffer full, dropped retry for address %" PRIu8, frame.address());
if (wfr.device != nullptr)
wfr.device->on_not_sent();
return;
}
// Re-queue a copy (not a move): the waiting entry may have to survive as an interrupted shell.
this->tx_buffer_.emplace_back(wfr.device, frame.address(), frame.pdu());
}
// Raw send for client: pushes to tx queue. Everything except the CRC must be contained in payload.
void ModbusClientHub::send_pdu(uint8_t address, std::span<const uint8_t> pdu, ModbusClientDevice *device) {
if (pdu.empty()) {
if (device)
device->on_not_sent();
return;
}
// Bound the PDU so the wire frame (address + pdu + CRC) stays within the Modbus RTU 256-byte limit.
if (pdu.size() > MAX_PDU_SIZE) {
ESP_LOGE(TAG, "Frame too large, dropped: %" PRIu8 ":%zu bytes", address, pdu.size());
if (device)
device->on_not_sent();
return;
}
if (this->tx_buffer_.size() < MODBUS_TX_BUFFER_SIZE) {
#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
char hex_buf[format_hex_pretty_size(MODBUS_MAX_LOG_BYTES)];
#endif
ESP_LOGV(TAG, "Adding frame to tx queue: %" PRIu8 ":%s", address,
format_hex_pretty_to(hex_buf, pdu.data(), pdu.size()));
this->tx_buffer_.emplace_back(device, address, pdu);
} else {
#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_ERROR
char hex_buf[format_hex_pretty_size(MODBUS_MAX_LOG_BYTES)];
#endif
ESP_LOGE(TAG, "Write buffer full, dropped: %" PRIu8 ":%s", address,
format_hex_pretty_to(hex_buf, pdu.data(), pdu.size()));
if (device)
device->on_not_sent();
}
}
void ModbusClientHub::clear_tx_queue_for_address(uint8_t address, bool clear_sent) {
// Remove any pending commands for this address from the tx buffer
auto &tx_buffer = this->tx_buffer_;
tx_buffer.erase(std::remove_if(tx_buffer.begin(), tx_buffer.end(),
[address](const ModbusDeviceCommand &cmd) { return cmd.frame.address() == address; }),
tx_buffer.end());
if (clear_sent && this->waiting_for_response_.has_value() && this->waiting_for_response_.value().device) {
if (this->waiting_for_response_.value().frame.address() == address) {
ESP_LOGV(TAG, "Clearing waiting for response for address %" PRIu8, address);
// Invalidate the waiting device so it won't process a response.
this->waiting_for_response_.value().device = nullptr;
}
}
}
void ModbusClientHub::clear_tx_queue_for_device(ModbusClientDevice *device) {
// Remove any pending commands for this address from the tx buffer
auto &tx_buffer = this->tx_buffer_;
tx_buffer.erase(std::remove_if(tx_buffer.begin(), tx_buffer.end(),
[device](const ModbusDeviceCommand &cmd) { return cmd.device == device; }),
tx_buffer.end());
if (this->waiting_for_response_.has_value() && this->waiting_for_response_.value().device) {
if (this->waiting_for_response_.value().device == device) {
ESP_LOGV(TAG, "Clearing waiting for response");
// Invalidate the waiting device so it won't process a response.
this->waiting_for_response_.value().device = nullptr;
}
}
}
void ModbusClientHub::send_raw(const std::vector<uint8_t> &payload, ModbusClientDevice *device) {
if (payload.size() < 2) {
if (device)
device->on_not_sent();
return;
}
this->send_pdu(payload[0], std::span<const uint8_t>(payload).subspan(1), device);
}
// Send raw command for server replies immediately. Except CRC everything must be contained in payload
void ModbusServerHub::send_raw_(const uint8_t *payload, uint16_t len) {
if (len == 0) {
return;
}
if (len > MAX_RAW_SIZE) {
ESP_LOGE(TAG, "Server send frame too large (%" PRIu16 " bytes)", len);
return;
}
// In the rare case that the server is blocked (frame delay has not elapsed), we delay the send.
// This should only happen at low baud rates with long frame delays.
if (this->tx_blocked()) {
// Stash the raw payload in a single member buffer so the deferred callback can rebuild the frame
// without a heap allocation. Only one server reply is ever in flight, and the named timeout ensures
// only one deferred send is pending, so a single buffer is sufficient.
std::memcpy(this->deferred_payload_.data(), payload, len);
this->deferred_payload_len_ = len;
this->set_timeout("deferred_send", this->tx_delay_remaining(), [this]() {
ModbusFrame frame(this->deferred_payload_[0], this->deferred_payload_.data() + 1,
this->deferred_payload_len_ - 1);
this->send_frame_(frame);
});
} else {
ModbusFrame frame(payload[0], payload + 1, len - 1);
this->send_frame_(frame);
}
}
void Modbus::clear_rx_buffer_(const LogString *reason, bool warn, size_t bytes_to_clear) {
size_t bytes = this->rx_buffer_.size();
if (bytes_to_clear > 0 && bytes >= bytes_to_clear)
bytes = bytes_to_clear;
if (bytes > 0) {
if (warn) {
ESP_LOGW(TAG, "Clearing buffer of %zu bytes - %s %" PRIu32 "ms after last send", bytes, LOG_STR_ARG(reason),
millis() - this->last_send_);
} else {
ESP_LOGV(TAG, "Clearing buffer of %zu bytes - %s %" PRIu32 "ms after last send", bytes, LOG_STR_ARG(reason),
millis() - this->last_send_);
}
if (bytes == this->rx_buffer_.size()) {
this->rx_buffer_.clear();
} else {
this->rx_buffer_.erase(this->rx_buffer_.begin(), this->rx_buffer_.begin() + bytes);
}
}
}
void ModbusClientDevice::read_entities(EntityType entity_type, uint16_t start_address, uint16_t number_of_entities) {
switch (entity_type) {
case EntityType::HOLDING:
this->read_holding_registers(start_address, number_of_entities);
return;
case EntityType::INPUT_REGISTER:
this->read_input_registers(start_address, number_of_entities);
return;
case EntityType::COIL:
this->read_coils(start_address, number_of_entities);
return;
case EntityType::DISCRETE_INPUT:
this->read_discrete_inputs(start_address, number_of_entities);
return;
default:
ESP_LOGW(TAG, "Invalid entity type for read_entities: %d", (int) entity_type);
this->on_not_sent(); // every rejected send is signalled, like send_pdu()'s own refusals
return;
}
}
} // namespace esphome::modbus
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