Add support for acting as Modbus server (#4874)

Co-authored-by: Jeroen van Oort <jeroen.vanoort@webparking.nl>
Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

esphome/components/modbus/__init__.py

@@ -1,5 +1,9 @@
+from __future__ import annotations
+from typing import Literal
+
 import esphome.codegen as cg
 import esphome.config_validation as cv
+import esphome.final_validate as fv
 from esphome.cpp_helpers import gpio_pin_expression
 from esphome.components import uart
 from esphome.const import (
@@ -17,13 +21,21 @@ Modbus = modbus_ns.class_("Modbus", cg.Component, uart.UARTDevice)
 ModbusDevice = modbus_ns.class_("ModbusDevice")
 MULTI_CONF = True
 
+CONF_ROLE = "role"
 CONF_MODBUS_ID = "modbus_id"
 CONF_SEND_WAIT_TIME = "send_wait_time"
 
+ModbusRole = modbus_ns.enum("ModbusRole")
+MODBUS_ROLES = {
+    "client": ModbusRole.CLIENT,
+    "server": ModbusRole.SERVER,
+}
+
 CONFIG_SCHEMA = (
     cv.Schema(
         {
             cv.GenerateID(): cv.declare_id(Modbus),
+            cv.Optional(CONF_ROLE, default="client"): cv.enum(MODBUS_ROLES),
             cv.Optional(CONF_FLOW_CONTROL_PIN): pins.gpio_output_pin_schema,
             cv.Optional(
                 CONF_SEND_WAIT_TIME, default="250ms"
@@ -43,6 +55,7 @@ async def to_code(config):
 
     await uart.register_uart_device(var, config)
 
+    cg.add(var.set_role(config[CONF_ROLE]))
     if CONF_FLOW_CONTROL_PIN in config:
         pin = await gpio_pin_expression(config[CONF_FLOW_CONTROL_PIN])
         cg.add(var.set_flow_control_pin(pin))
@@ -62,6 +75,28 @@ def modbus_device_schema(default_address):
     return cv.Schema(schema)
 
 
+def final_validate_modbus_device(
+    name: str, *, role: Literal["server", "client"] | None = None
+):
+    def validate_role(value):
+        assert role in MODBUS_ROLES
+        if value != role:
+            raise cv.Invalid(f"Component {name} requires role to be {role}")
+        return value
+
+    def validate_hub(hub_config):
+        hub_schema = {}
+        if role is not None:
+            hub_schema[cv.Required(CONF_ROLE)] = validate_role
+
+        return cv.Schema(hub_schema, extra=cv.ALLOW_EXTRA)(hub_config)
+
+    return cv.Schema(
+        {cv.Required(CONF_MODBUS_ID): fv.id_declaration_match_schema(validate_hub)},
+        extra=cv.ALLOW_EXTRA,
+    )
+
+
 async def register_modbus_device(var, config):
     parent = await cg.get_variable(config[CONF_MODBUS_ID])
     cg.add(var.set_parent(parent))

esphome/components/modbus/modbus.cpp

@@ -77,7 +77,13 @@ bool Modbus::parse_modbus_byte_(uint8_t byte) {
     ESP_LOGD(TAG, "Modbus user-defined function %02X found", function_code);
 
   } else {
-    // the response for write command mirrors the requests and data startes at offset 2 instead of 3 for read commands
+    // data starts at 2 and length is 4 for read registers commands
+    if (this->role == ModbusRole::SERVER && (function_code == 0x3 || function_code == 0x4)) {
+      data_offset = 2;
+      data_len = 4;
+    }
+
+    // the response for write command mirrors the requests and data starts at offset 2 instead of 3 for read commands
     if (function_code == 0x5 || function_code == 0x06 || function_code == 0xF || function_code == 0x10) {
       data_offset = 2;
       data_len = 4;
@@ -123,6 +129,9 @@ bool Modbus::parse_modbus_byte_(uint8_t byte) {
           // Ignore modbus exception not related to a pending command
           ESP_LOGD(TAG, "Ignoring Modbus error - not expecting a response");
         }
+      } else if (this->role == ModbusRole::SERVER && (function_code == 0x3 || function_code == 0x4)) {
+        device->on_modbus_read_registers(function_code, uint16_t(data[1]) | (uint16_t(data[0]) << 8),
+                                         uint16_t(data[3]) | (uint16_t(data[2]) << 8));
       } else {
         device->on_modbus_data(data);
       }
@@ -164,16 +173,18 @@ void Modbus::send(uint8_t address, uint8_t function_code, uint16_t start_address
   std::vector<uint8_t> data;
   data.push_back(address);
   data.push_back(function_code);
-  data.push_back(start_address >> 8);
-  data.push_back(start_address >> 0);
-  if (function_code != 0x5 && function_code != 0x6) {
-    data.push_back(number_of_entities >> 8);
-    data.push_back(number_of_entities >> 0);
+  if (this->role == ModbusRole::CLIENT) {
+    data.push_back(start_address >> 8);
+    data.push_back(start_address >> 0);
+    if (function_code != 0x5 && function_code != 0x6) {
+      data.push_back(number_of_entities >> 8);
+      data.push_back(number_of_entities >> 0);
+    }
   }
 
   if (payload != nullptr) {
-    if (function_code == 0xF || function_code == 0x10) {  // Write multiple
-      data.push_back(payload_len);                        // Byte count is required for write
+    if (this->role == ModbusRole::SERVER || function_code == 0xF || function_code == 0x10) {  // Write multiple
+      data.push_back(payload_len);  // Byte count is required for write
     } else {
       payload_len = 2;  // Write single register or coil
     }

esphome/components/modbus/modbus.h

@@ -8,6 +8,11 @@
 namespace esphome {
 namespace modbus {
 
+enum ModbusRole {
+  CLIENT,
+  SERVER,
+};
+
 class ModbusDevice;
 
 class Modbus : public uart::UARTDevice, public Component {
@@ -27,11 +32,14 @@ class Modbus : public uart::UARTDevice, public Component {
   void send(uint8_t address, uint8_t function_code, uint16_t start_address, uint16_t number_of_entities,
             uint8_t payload_len = 0, const uint8_t *payload = nullptr);
   void send_raw(const std::vector<uint8_t> &payload);
+  void set_role(ModbusRole role) { this->role = role; }
   void set_flow_control_pin(GPIOPin *flow_control_pin) { this->flow_control_pin_ = flow_control_pin; }
   uint8_t waiting_for_response{0};
   void set_send_wait_time(uint16_t time_in_ms) { send_wait_time_ = time_in_ms; }
   void set_disable_crc(bool disable_crc) { disable_crc_ = disable_crc; }
 
+  ModbusRole role;
+
  protected:
   GPIOPin *flow_control_pin_{nullptr};
 
@@ -50,6 +58,7 @@ class ModbusDevice {
   void set_address(uint8_t address) { address_ = address; }
   virtual void on_modbus_data(const std::vector<uint8_t> &data) = 0;
   virtual void on_modbus_error(uint8_t function_code, uint8_t exception_code) {}
+  virtual void on_modbus_read_registers(uint8_t function_code, uint16_t start_address, uint16_t number_of_registers){};
   void send(uint8_t function, uint16_t start_address, uint16_t number_of_entities, uint8_t payload_len = 0,
             const uint8_t *payload = nullptr) {
     this->parent_->send(this->address_, function, start_address, number_of_entities, payload_len, payload);