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[modbus_client] Add read/write multiple registers (FC 0x17) (#18215)

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This commit is contained in:
Bonne Eggleston
2026-08-10 15:18:48 -05:00
committed by GitHub
parent 8a16ead8ce
commit 596827c51c
12 changed files with 520 additions and 52 deletions
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esphome/components/modbus/modbus.cpp
+18 -5
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@@ -382,7 +382,7 @@ ModbusServerDevice *ModbusServerHub::find_device_(uint8_t address) {
}
ResponseStatus ModbusServerHub::check_address_range_(uint16_t start_address, uint16_t count) {
if ((uint32_t) start_address + count > 0x10000u) {
if (!helpers::address_range_fits(start_address, count)) {
ESP_LOGW(TAG, "Address out of range - start: %" PRIu16 " num: %" PRIu16, start_address, count);
return ExceptionCode::ILLEGAL_DATA_ADDRESS;
}
@@ -1056,7 +1056,8 @@ bool ModbusClientHub::queue_pdu(uint8_t address, std::span<const uint8_t> pdu, M
continue;
if (device == nullptr) {
// A dropped read is routine (DEBUG); a dropped write/custom warns (unobservable without a device).
const bool requeueable = !helpers::is_function_code_exception(pdu[0]) && helpers::is_function_code_read(pdu[0]);
const bool requeueable =
!helpers::is_function_code_exception(pdu[0]) && helpers::is_function_code_read_only(pdu[0]);
if (requeueable) {
ESP_LOGD(TAG, "Anonymous duplicate of active frame for %" PRIu8 " (function 0x%X), dropped", address, pdu[0]);
} else {
@@ -1236,7 +1237,14 @@ void ModbusClientDevice::dispatch_response_(std::span<const uint8_t> request_pdu
switch (function_code) {
case FunctionCode::READ_HOLDING_REGISTERS:
case FunctionCode::READ_INPUT_REGISTERS: {
case FunctionCode::READ_INPUT_REGISTERS:
// FC 0x17 lands here too: its read start address and read quantity sit at the same request offsets as a
// plain read's (bytes 1..2 and 3..4), so start_address and count_or_value already hold the read block; its
// response carries only that read data, and the write half is confirmed by the response arriving at all.
// An exception routes here as well (the gate only validates the request when status is set), delivering
// empty registers with the error in status - so a 0x17 subclass handles success and failure in the one
// on_read_holding_registers() callback and never needs to also override on_error().
case FunctionCode::READ_WRITE_MULTIPLE_REGISTERS: {
// Decode the big-endian register words into host byte order. The gate guarantees a success response
// carries exactly count_or_value registers (and count_or_value <= MAX_NUM_OF_REGISTERS_TO_READ, the
// capacity of RegisterValues); a mismatch was diverted to on_custom_response(), never clamped. On
@@ -1248,10 +1256,15 @@ void ModbusClientDevice::dispatch_response_(std::span<const uint8_t> request_pdu
}
}
std::span<const uint16_t> register_span(registers.data(), registers.size());
if (function_code == FunctionCode::READ_HOLDING_REGISTERS) {
if (function_code == FunctionCode::READ_INPUT_REGISTERS) {
this->on_read_input_registers(start_address, register_span, status);
} else if (function_code == FunctionCode::READ_HOLDING_REGISTERS ||
function_code == FunctionCode::READ_WRITE_MULTIPLE_REGISTERS) {
this->on_read_holding_registers(start_address, register_span, status);
} else {
this->on_read_input_registers(start_address, register_span, status);
// Unreachable for the current case labels; match explicitly so a function code added to this group
// later is diverted to on_custom_response() rather than silently delivered as a holding read.
this->on_custom_response(request_pdu, response_pdu, status);
}
break;
}