feat(modbus): Bring freemodbus component and example from IDF

Commit ID: d0b9829e

components/freemodbus/common/esp_modbus_slave_serial.c

@@ -0,0 +1,44 @@
+/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+ *
+ * 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
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.
+ */
+
+#include "esp_err.h"                    // for esp_err_t
+#include "sdkconfig.h"                  // for KConfig defines
+#include "mbc_slave.h"                  // for slave interface define
+#include "esp_modbus_slave.h"           // for public slave defines
+#include "mbc_serial_slave.h"           // for public interface defines
+
+/**
+ * Initialization of Modbus Serial slave controller
+ */
+esp_err_t mbc_slave_init(mb_port_type_t port_type, void** handler)
+{
+    void* port_handler = NULL;
+    esp_err_t error = ESP_ERR_NOT_SUPPORTED;
+    switch(port_type)
+    {
+        case MB_PORT_SERIAL_SLAVE:
+            // Call constructor function of actual port implementation
+            error = mbc_serial_slave_create(&port_handler);
+            break;
+        default:
+            return ESP_ERR_NOT_SUPPORTED;
+    }
+    if ((port_handler != NULL) && (error == ESP_OK)) {
+        mbc_slave_init_iface(port_handler);
+        *handler = port_handler;
+    }
+    return error;
+}
+