fix: address maximum api blocking time

Kconfig

@@ -71,12 +71,21 @@ menu "Modbus configuration"
 
     config FMB_MASTER_TIMEOUT_MS_RESPOND
         int "Slave respond timeout (Milliseconds)"
-        default 10000
+        default 5000
         range 150 30000
         help
                 If master sends a frame which is not broadcast, it has to wait some time for slave response.
                 if slave is not respond in this time, the master will process timeout error.
 
+    config FMB_MASTER_MAX_API_BLOCKING_TIME_MS
+        int "Modbus TCP master API blocking threshold (ms)"
+        range 3000 200000
+        default 6000
+        help
+                This option represents the maximum API blocking time used by controller API calls.
+                This API blocking time was intentionally separated from master timeout = CONFIG_FMB_MASTER_TIMEOUT_MS_RESPOND
+                to prevent possible misconfiguration and the value must be higher than the master timeout.
+
     config FMB_MASTER_DELAY_MS_CONVERT
         int "Slave conversion delay (Milliseconds)"
         default 200

modbus/mb_controller/common/esp_modbus_master.c

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2016-2023 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2016-2026 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -13,6 +13,8 @@
 
 static const char TAG[] __attribute__((unused)) = "MB_CONTROLLER_MASTER";
 
+#define API_BLOCKING_THRESHOLD 500
+
 // This file implements public API for Modbus master controller.
 
 /**
@@ -203,6 +205,20 @@ esp_err_t mbc_master_start(void *ctx)
     MB_RETURN_ON_FALSE(ctx, ESP_ERR_INVALID_STATE, TAG,
                        "Master interface is not correctly initialized.");
     mbm_controller_iface_t *mbm_controller = MB_MASTER_GET_IFACE(ctx);
+
+    uint32_t response_tout_ms = mbm_controller->opts.comm_opts.common_opts.response_tout_ms;
+    // Keep stack response timeout below API blocking threshold
+    if (!response_tout_ms || (response_tout_ms >= CONFIG_FMB_MASTER_MAX_API_BLOCKING_TIME_MS)) {
+        response_tout_ms = (CONFIG_FMB_MASTER_TIMEOUT_MS_RESPOND
+                            <= (CONFIG_FMB_MASTER_MAX_API_BLOCKING_TIME_MS - API_BLOCKING_THRESHOLD))
+                           ? CONFIG_FMB_MASTER_TIMEOUT_MS_RESPOND
+                           : (CONFIG_FMB_MASTER_MAX_API_BLOCKING_TIME_MS - API_BLOCKING_THRESHOLD);
+        ESP_LOGW(TAG,
+                 "Master timeout option = (%u) exceeded the maximum API threshold or is uninitialized, will be set to configured value = %u.",
+                 (unsigned)mbm_controller->opts.comm_opts.common_opts.response_tout_ms, (unsigned)response_tout_ms);
+        mbm_controller->opts.comm_opts.common_opts.response_tout_ms = response_tout_ms;
+    }
+
     MB_RETURN_ON_FALSE(mbm_controller->start, ESP_ERR_INVALID_STATE, TAG,
                        "Master interface is not correctly initialized.");
     error = mbm_controller->start(ctx);

modbus/mb_controller/common/mbc_master.h

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2016-2023 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2016-2026 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -22,16 +22,26 @@
 #include "mb_utils.h"
 #include "mb_master.h"
 
+#include "sdkconfig.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 /* ----------------------- Defines ------------------------------------------*/
+#define MB_MIN_RESP_DELAY_MS (300)
 
 // Set the maximum resource waiting time, the actual time of resource release
-// will be dependent on response time set by timer + conversion time if the command is received
-#define MB_MAX_RESP_DELAY_MS (3000)
-#define MB_MIN_RESP_DELAY_MS (300)
+// will be dependent on response time set by timer + conversion time if the command is received.
+#if defined(CONFIG_FMB_MASTER_MAX_API_BLOCKING_TIME_MS)
+#define MB_MAX_RESP_DELAY_MS (CONFIG_FMB_MASTER_MAX_API_BLOCKING_TIME_MS)
+_Static_assert(
+    (CONFIG_FMB_MASTER_MAX_API_BLOCKING_TIME_MS) >= (CONFIG_FMB_MASTER_TIMEOUT_MS_RESPOND),
+    "CONFIG_FMB_MASTER_MAX_API_BLOCKING_TIME_MS must be >= CONFIG_FMB_MASTER_TIMEOUT_MS_RESPOND"
+);
+#else
+#define MB_MAX_RESP_DELAY_MS (CONFIG_FMB_MASTER_TIMEOUT_MS_RESPOND)
+#endif
 
 /**
  * @brief Modbus controller handler structure

modbus/mb_objects/common/mb_port_types.h

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2021-2023 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2021-2026 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -37,11 +37,15 @@ typedef enum mb_comm_mode_enum mb_mode_type_t;
 
 #if (CONFIG_FMB_COMM_MODE_ASCII_EN || CONFIG_FMB_COMM_MODE_RTU_EN)
 
+#include <stddef.h>
 #include "driver/uart.h"
 
 struct port_serial_opts_s {
     mb_mode_type_t mode;            /*!< Modbus communication mode */
-    uart_port_t port;               /*!< Modbus communication port (UART) number */
+    union {
+        uart_port_t port;           /*!< UART driver port index (user API) */
+        uint32_t ser_port_align;    /*!< Overlay for union with TCP/common \c port field */
+    };
     uint8_t uid;                    /*!< Modbus slave address field (dummy for master) */
     uint32_t response_tout_ms;      /*!< Modbus slave response timeout */
     uint64_t test_tout_us;          /*!< Modbus test timeout (reserved) */
@@ -63,7 +67,7 @@ typedef enum addr_type_enum {
 
 struct port_common_opts_s {
     mb_mode_type_t mode;            /*!< Modbus communication mode */
-    uint16_t port;                  /*!< Modbus communication port (UART) number */
+    uint32_t port;                  /*!< Modbus port number (TCP) or UART index (serial) */
     uint8_t uid;                    /*!< Modbus slave address field (dummy for master) */
     uint32_t response_tout_ms;      /*!< Modbus slave response timeout */
     uint64_t test_tout_us;          /*!< Modbus test timeout (reserved) */
@@ -71,7 +75,10 @@ struct port_common_opts_s {
 
 struct port_tcp_opts_s {
     mb_mode_type_t mode;            /*!< Modbus communication mode */
-    uint16_t port;                  /*!< Modbus communication port (UART) number */
+    struct {
+        uint16_t port;              /*!< Modbus port number (TCP) */
+        uint16_t tcp_port_align;    /*!< Overlay for union with SERIAL/common \c port field */
+    };
     uint8_t uid;                    /*!< Modbus slave address field (dummy for master) */
     uint32_t response_tout_ms;      /*!< Modbus slave response timeout */
     uint64_t test_tout_us;          /*!< Modbus test timeout (reserved) */
@@ -84,6 +91,18 @@ struct port_tcp_opts_s {
 
 typedef struct port_tcp_opts_s mb_tcp_opts_t;
 
+#if (CONFIG_FMB_COMM_MODE_ASCII_EN || CONFIG_FMB_COMM_MODE_RTU_EN)
+_Static_assert(sizeof(uart_port_t) == sizeof(uint32_t),
+               "uart_port_t must match uint32_t width of common/tcp port for mb_communication_info_t union");
+_Static_assert(offsetof(struct port_serial_opts_s, response_tout_ms) == offsetof(struct port_common_opts_s, response_tout_ms),
+               "serial/common Modbus opts: response_tout_ms offset must match (mb_communication_info_t union)");
+#endif
+
+#if (CONFIG_FMB_COMM_MODE_TCP_EN) && (CONFIG_FMB_COMM_MODE_ASCII_EN || CONFIG_FMB_COMM_MODE_RTU_EN)
+_Static_assert(offsetof(struct port_serial_opts_s, response_tout_ms) == offsetof(struct port_tcp_opts_s, response_tout_ms),
+               "serial/tcp Modbus opts: response_tout_ms offset must match (mb_communication_info_t union)");
+#endif
+
 // The common object descriptor structure (common for mb, transport, port objects)
 struct obj_descr_s {
     char *parent_name;              /*!< Name of the parent (base) object */