fix(modem): Support for custom modules with C-API

MAJOR CHANGE: Added support for implementing user defined modules in standard C-API

components/esp_modem/CMakeLists.txt

@@ -42,6 +42,9 @@ set_target_properties(${COMPONENT_LIB} PROPERTIES
     CXX_EXTENSIONS ON
 )
 
+if(CONFIG_ESP_MODEM_ADD_CUSTOM_MODULE)
+    idf_component_optional_requires(PUBLIC main)
+endif()
 
 if(${target} STREQUAL "linux")
     # This is needed for ESP_LOGx() macros, as integer formats differ on ESP32(..) and x64

components/esp_modem/Kconfig

@@ -45,4 +45,22 @@ menu "esp-modem"
             to make the protocol more robust on noisy environments or when underlying
             transport gets corrupted often (for example by Rx buffer overflows)
 
+    config ESP_MODEM_ADD_CUSTOM_MODULE
+        bool "Add support for custom module in C-API"
+        default n
+        help
+            If enabled, we adapt the C-API to create a DCE from a user defined class
+
+    config ESP_MODEM_CUSTOM_MODULE_HEADER
+        string "Header file name which defines custom DCE creation"
+        depends on ESP_MODEM_ADD_CUSTOM_MODULE
+        default "custom_module.hpp"
+        help
+            Name of the header file in the main component which implements esp_modem_create_custom_dce()
+            called from C-API for creating esp_modem_dce object.
+            This header provides definition of the custom module with some additional and/or updated commands
+            and API. It also defines creation of DCE based on this custom module, typically calling:
+            dce_factory::Factory::create_unique_dce_from<CustomModule, DCE*>(dce_config, std::move(dte), netif)
+            Please refer to the pppos_client example for more details.
+
 endmenu

components/esp_modem/examples/pppos_client/main/Kconfig.projbuild

@@ -48,6 +48,13 @@ menu "Example Configuration"
             bool "A7670"
             help
                 A7670X is Multi-Band LTE-FDD/LTE-TDD/GSM/GPRS/EDGE module.
+
+        config EXAMPLE_MODEM_DEVICE_CUSTOM
+            select ESP_MODEM_ADD_CUSTOM_MODULE
+            bool "Custom device"
+            help
+                This demonstrates use of a custom device in C-API.
+
     endchoice
 
     config EXAMPLE_MODEM_PPP_APN

components/esp_modem/examples/pppos_client/main/custom_module.hpp

@@ -0,0 +1,79 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Unlicense OR CC0-1.0
+ */
+
+#pragma once
+#include "cxx_include/esp_modem_api.hpp"
+#include "cxx_include/esp_modem_command_library_utils.hpp"
+
+/**
+ * @brief Definition of a custom module based on some already defined module
+ *          Here we use GenericModule, but you can use any kind of device
+ *          that is closer to your CustomModule.
+ */
+class SIM7600_WITH_TIME: public GenericModule {
+    /**
+     * @brief Need to reuse the constructors of our ancestor
+     */
+    using GenericModule::GenericModule;
+public:
+    /**
+     * @brief New command that is not defined in the GenericModule
+     */
+    command_result get_time(std::string &time)
+    {
+        return esp_modem::dce_commands::generic_get_string(dte.get(), "AT+CCLK?\r", time);
+    }
+
+    /**
+     * @brief This command is already defined in the GenericModule
+     *
+     * Here we just modify get_signal_quality() to return zeroes
+     * for demonstration purpose only, since it's called within this example
+     */
+    command_result get_signal_quality(int &rssi, int &ber) override
+    {
+        rssi = ber = 0;
+        return esp_modem::command_result::OK;
+    }
+
+};
+
+/**
+ * @brief esp_modem_create_custom_dce() needs to be defined, as it is called in C-API wrapper when creating esp_modem_dce
+ *
+ * This uses public factory function for creating a common DCE with our CustomModule. Creating raw DCE pointer is only needed
+ * for the C-API wrapper; C++API users would create DCE (any kind of smart pointer) directly with
+ * Factory::create_unique_dce_from<CustomModule>(dce_config, std::move(dte), netif);
+ */
+DCE *esp_modem_create_custom_dce(const esp_modem_dce_config_t *dce_config, std::shared_ptr<DTE> dte, esp_netif_t *netif)
+{
+    return dce_factory::Factory::create_unique_dce_from<SIM7600_WITH_TIME, DCE *>(dce_config, std::move(dte), netif);
+}
+
+/**
+ * @brief This API is only needed for extending standard C-API, since we added get_time() method to our CustomModule
+ *
+ * @note This header is included from esp_modem_c_api.cpp, so it could use ESP_MODEM_C_API_STR_MAX macro
+ * indicating maximum C-API string size
+ *
+ * @note In order to access the newly added API get_time(), we have to static_cast<> the GenericModule from DCE
+ * to our CustomModule.
+ * Alternatively we could use the modem Factory to build our specific DCE_T<CustomModule>, but in that case
+ * we couldn't use our C-API wrappers which expect DCE type, DCE_T<GenericModule> with lib commands (this alternative
+ * is cleaner, but more suitable for C++ users)
+ */
+extern "C" esp_err_t esp_modem_get_time(esp_modem_dce_t *dce_wrap, char *p_time)
+{
+    if (dce_wrap == nullptr || dce_wrap->dce == nullptr) {
+        return ESP_ERR_INVALID_ARG;
+    }
+    std::string time{ESP_MODEM_C_API_STR_MAX};
+    auto ret = command_response_to_esp_err(static_cast<SIM7600_WITH_TIME *>(dce_wrap->dce->get_module())->get_time(time));
+    if (ret == ESP_OK && !time.empty()) {
+        strlcpy(p_time, time.c_str(), ESP_MODEM_C_API_STR_MAX);
+    }
+    return ret;
+}

components/esp_modem/examples/pppos_client/main/pppos_client_main.c

@@ -37,6 +37,10 @@ static const int CONNECT_BIT = BIT0;
 static const int GOT_DATA_BIT = BIT2;
 static const int USB_DISCONNECTED_BIT = BIT3; // Used only with USB DTE but we define it unconditionally, to avoid too many #ifdefs in the code
 
+#ifdef CONFIG_EXAMPLE_MODEM_DEVICE_CUSTOM
+esp_err_t esp_modem_get_time(esp_modem_dce_t *dce_wrap, char *p_time);
+#endif
+
 #if defined(CONFIG_EXAMPLE_SERIAL_CONFIG_USB)
 #include "esp_modem_usb_c_api.h"
 #include "esp_modem_usb_config.h"
@@ -192,6 +196,9 @@ void app_main(void)
 #elif CONFIG_EXAMPLE_MODEM_DEVICE_SIM7600 == 1
     ESP_LOGI(TAG, "Initializing esp_modem for the SIM7600 module...");
     esp_modem_dce_t *dce = esp_modem_new_dev(ESP_MODEM_DCE_SIM7600, &dte_config, &dce_config, esp_netif);
+#elif CONFIG_EXAMPLE_MODEM_DEVICE_CUSTOM == 1
+    ESP_LOGI(TAG, "Initializing esp_modem with custom module...");
+    esp_modem_dce_t *dce = esp_modem_new_dev(ESP_MODEM_DCE_CUSTOM, &dte_config, &dce_config, esp_netif);
 #else
     ESP_LOGI(TAG, "Initializing esp_modem for a generic module...");
     esp_modem_dce_t *dce = esp_modem_new(&dte_config, &dce_config, esp_netif);
@@ -258,6 +265,18 @@ void app_main(void)
     }
     ESP_LOGI(TAG, "Signal quality: rssi=%d, ber=%d", rssi, ber);
 
+#ifdef CONFIG_EXAMPLE_MODEM_DEVICE_CUSTOM
+    {
+        char time[64];
+        err = esp_modem_get_time(dce, time);
+        if (err != ESP_OK) {
+            ESP_LOGE(TAG, "esp_modem_get_time failed with %d %s", err, esp_err_to_name(err));
+            return;
+        }
+        ESP_LOGI(TAG, "esp_modem_get_time: %s", time);
+    }
+#endif
+
 #if CONFIG_EXAMPLE_SEND_MSG
     if (esp_modem_sms_txt_mode(dce, true) != ESP_OK || esp_modem_sms_character_set(dce) != ESP_OK) {
         ESP_LOGE(TAG, "Setting text mode or GSM character set failed");

components/esp_modem/include/cxx_include/esp_modem_dce_factory.hpp

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2021-2023 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -12,6 +12,7 @@
  * @brief DCE modem factory
  */
 
+#define esp_modem_create_dce_from dce_factory::Factory::create_unique_dce_from
 
 namespace esp_modem::dce_factory {
 
@@ -236,12 +237,12 @@ public:
         return nullptr;
     }
 
-    template <typename T_Module>
-    static std::unique_ptr<DCE> create_unique_dce_from(const esp_modem::dce_config *config,
-            std::shared_ptr<esp_modem::DTE> dte,
-            esp_netif_t *netif)
+    template <typename T_Module, typename Ptr = std::unique_ptr<DCE>>
+    static Ptr create_unique_dce_from(const esp_modem::dce_config *config,
+                                      std::shared_ptr<esp_modem::DTE> dte,
+                                      esp_netif_t *netif)
     {
-        return build_generic_DCE<T_Module, DCE, std::unique_ptr<DCE>>(config, std::move(dte), netif);
+        return build_generic_DCE<T_Module, DCE, Ptr>(config, std::move(dte), netif);
     }
 
 private:

components/esp_modem/include/esp_modem_c_api_types.h

@@ -53,6 +53,7 @@ typedef enum esp_modem_dce_device {
     ESP_MODEM_DCE_SIM7000,
     ESP_MODEM_DCE_BG96,
     ESP_MODEM_DCE_SIM800,
+    ESP_MODEM_DCE_CUSTOM
 } esp_modem_dce_device_t;
 
 /**

components/esp_modem/src/esp_modem_c_api.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include <cstring>
 #include <cassert>
 #include "cxx_include/esp_modem_dte.hpp"
 #include "uart_terminal.hpp"
@@ -14,7 +15,6 @@
 #include "esp_modem_config.h"
 #include "exception_stub.hpp"
 #include "esp_private/c_api_wrapper.hpp"
-#include "cstring"
 
 #ifndef ESP_MODEM_C_API_STR_MAX
 #define ESP_MODEM_C_API_STR_MAX 64
@@ -24,6 +24,10 @@
 size_t strlcpy(char *dest, const char *src, size_t len);
 #endif
 
+#ifdef CONFIG_ESP_MODEM_ADD_CUSTOM_MODULE
+#include CONFIG_ESP_MODEM_CUSTOM_MODULE_HEADER
+#endif
+
 //
 // C API definitions
 using namespace esp_modem;
@@ -40,8 +44,15 @@ extern "C" esp_modem_dce_t *esp_modem_new_dev(esp_modem_dce_device_t module, con
         return nullptr;
     }
     dce_wrap->dte = dte;
-    dce_factory::Factory f(convert_modem_enum(module));
-    dce_wrap->dce = f.build(dce_config, std::move(dte), netif);
+#ifdef CONFIG_ESP_MODEM_ADD_CUSTOM_MODULE
+    if (module == ESP_MODEM_DCE_CUSTOM) {
+        dce_wrap->dce = esp_modem_create_custom_dce(dce_config, dte, netif);
+    } else
+#endif
+    {
+        dce_factory::Factory f(convert_modem_enum(module));
+        dce_wrap->dce = f.build(dce_config, std::move(dte), netif);
+    }
     if (dce_wrap->dce == nullptr) {
         delete dce_wrap;
         return nullptr;

docs/esp_modem/en/README.rst

@@ -110,6 +110,10 @@ commands might have a different implementation. Adding a new device
 means to provide a new implementation as a class derived from
 ``GenericModule``, where we could add new commands or modify the
 existing ones.
+If you have to support a custom device with C-API, please refer to
+the example ``examples/pppos_client`` and enable ``ESP_MODEM_ADD_CUSTOM_MODULE``.
+For advanced use-case, mainly with C++ API and/or usage of esp_modem's
+Factory class, please read <advanced_api>.
 
 Configuration
 -------------