feat(modem): Add support for guessing mode

components/esp_modem/include/cxx_include/esp_modem_dce.hpp

@@ -30,9 +30,11 @@ class DCE_Mode {
     ~DCE_Mode() = default;
     bool set(DTE *dte, ModuleIf *module, Netif &netif, modem_mode m);
     modem_mode get();
+    modem_mode guess(DTE *dte, bool with_cmux = false);
 
 private:
     bool set_unsafe(DTE *dte, ModuleIf *module, Netif &netif, modem_mode m);
+    modem_mode guess_unsafe(DTE *dte, bool with_cmux);
     modem_mode mode;
 
 };
@@ -79,6 +81,11 @@ class DCE_T {
         return dte->command(command, std::move(got_line), time_ms);
     }
 
+    modem_mode guess_mode(bool with_cmux = false)
+    {
+        return mode.guess(dte.get(), with_cmux);
+    }
+
     bool set_mode(modem_mode m)
     {
         return mode.set(dte.get(), device.get(), netif, m);

components/esp_modem/include/cxx_include/esp_modem_dte.hpp

@@ -65,6 +65,18 @@ class DTE : public CommandableIf {
 
     int write(DTE_Command command);
 
+    /**
+     * @brief send data to the selected terminal, by default (without term_id argument)
+     * this API works the same as write: sends data to the secondary terminal, which is
+     * typically used as data terminal (for networking).
+     *
+     * @param data Data pointer to write
+     * @param len Data len to write
+     * @param term_id Terminal id: Primary if id==0, Secondary if id==1
+     * @return number of bytes written
+     */
+    int send(uint8_t *data, size_t len, int term_id = 1);
+
     /**
      * @brief Reading from the underlying terminal
      * @param d Returning the data pointer of the received payload

components/esp_modem/include/cxx_include/esp_modem_types.hpp

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2021-2024 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -37,6 +37,17 @@ enum class modem_mode {
     CMUX_MANUAL_DATA,    /*!< Sets the primary terminal to DATA mode in manual CMUX */
     CMUX_MANUAL_COMMAND, /*!< Sets the primary terminal to COMMAND mode in manual CMUX */
     CMUX_MANUAL_SWAP,    /*!< Swaps virtual terminals in manual CMUX mode (primary <-> secondary) */
+    RESUME_DATA_MODE,    /*!< This is used when the device is already in DATA mode and we need the modem lib to
+                          * enter the mode without switching. On success, we would end up in DATA-mode, UNDEF otherwise */
+    RESUME_COMMAND_MODE, /*!< This is used when the device is already in COMMAND mode and we want to resume it
+                          * On success, we would end up in DATA-mode, UNDEF otherwise */
+    RESUME_CMUX_MANUAL_MODE, /*!< This is used when the device is already in CMUX mode and we need the modem lib to
+                              * enter it without switching. On success, we would end up in CMUX_MANUAL-mode, UNDEF otherwise */
+    RESUME_CMUX_MANUAL_DATA, /*!< This is used when the device is already in CMUX-DATA mode and we need the modem lib to
+                              * enter it without switching. On success, we would end up in CMUX_MANUAL-DATA mode, UNDEF otherwise */
+    AUTODETECT,              /*!< Auto-detection command: It tries to send a few packets in order to recognize which mode the
+                              * the device currently is and update the modem library mode. On success the modem is updated,
+                              * otherwise it's set to UNDEF */
 };
 
 /**

components/esp_modem/src/esp_modem_dce.cpp

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2021-2023 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2021-2024 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -103,6 +103,51 @@ bool DCE_Mode::set_unsafe(DTE *dte, ModuleIf *device, Netif &netif, modem_mode m
         return true;
     case modem_mode::DUAL_MODE: // Only DTE can be in Dual mode
         break;
+    case modem_mode::AUTODETECT: {
+        auto guessed = guess_unsafe(dte, true);
+        if (guessed == modem_mode::UNDEF) {
+            return false;
+        }
+        // prepare the undefined mode before to allow all possible transitions
+        if (!dte->set_mode(modem_mode::UNDEF)) {
+            return false;
+        }
+        mode = modem_mode::UNDEF;
+        ESP_LOGD("DCE mode", "Detected mode: %d", static_cast<int>(guessed));
+        if (guessed == modem_mode::DATA_MODE) {
+            return set_unsafe(dte, device, netif, esp_modem::modem_mode::RESUME_DATA_MODE);
+        } else if (guessed == esp_modem::modem_mode::COMMAND_MODE) {
+            return set_unsafe(dte, device, netif, esp_modem::modem_mode::RESUME_COMMAND_MODE);
+        } else if (guessed == esp_modem::modem_mode::CMUX_MODE) {
+            if (!set_unsafe(dte, device, netif, esp_modem::modem_mode::RESUME_CMUX_MANUAL_MODE)) {
+                return false;
+            }
+            // now we guess the mode for each terminal
+            guessed = guess_unsafe(dte, false);
+            ESP_LOGD("DCE mode", "Detected mode on primary term: %d", static_cast<int>(guessed));
+            // now we need to access the second terminal, so we could simply send a SWAP command
+            // (switching to data mode does the swapping internally, so we only swap if we're in CMD mode)
+            if (guessed == modem_mode::DATA_MODE) {
+                // switch to DATA on the primary terminal and swap terminals
+                if (!set_unsafe(dte, device, netif, esp_modem::modem_mode::RESUME_CMUX_MANUAL_DATA)) {
+                    return false;
+                }
+            } else {
+                // swap terminals
+                if (!set_unsafe(dte, device, netif, esp_modem::modem_mode::CMUX_MANUAL_SWAP)) {
+                    return false;
+                }
+            }
+            guessed = guess_unsafe(dte, false);
+            ESP_LOGD("DCE mode", "Detected mode on secondary term: %d", static_cast<int>(guessed));
+            if (guessed == modem_mode::DATA_MODE) {
+                if (!set_unsafe(dte, device, netif, esp_modem::modem_mode::RESUME_CMUX_MANUAL_DATA)) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
     case modem_mode::COMMAND_MODE:
         if (mode == modem_mode::COMMAND_MODE || mode >= modem_mode::CMUX_MANUAL_MODE) {
             return false;
@@ -122,6 +167,32 @@ bool DCE_Mode::set_unsafe(DTE *dte, ModuleIf *device, Netif &netif, modem_mode m
         }
         mode = m;
         return true;
+    case modem_mode::RESUME_DATA_MODE:
+        if (!dte->set_mode(modem_mode::DATA_MODE)) {
+            return false;
+        }
+        netif.start();
+        mode = modem_mode::DATA_MODE;
+        return true;
+    case modem_mode::RESUME_COMMAND_MODE:
+        if (!dte->set_mode(modem_mode::COMMAND_MODE)) {
+            return false;
+        }
+        mode = modem_mode::COMMAND_MODE;
+        return true;
+    case modem_mode::RESUME_CMUX_MANUAL_MODE:
+        if (!dte->set_mode(modem_mode::CMUX_MANUAL_MODE)) {
+            return false;
+        }
+        mode = modem_mode::CMUX_MANUAL_MODE;
+        return true;
+    case modem_mode::RESUME_CMUX_MANUAL_DATA:
+        if (!dte->set_mode(modem_mode::CMUX_MANUAL_SWAP)) {
+            return false;
+        }
+        netif.start();
+        mode = modem_mode::CMUX_MANUAL_MODE;
+        return true;
     case modem_mode::DATA_MODE:
         if (mode == modem_mode::DATA_MODE || mode == modem_mode::CMUX_MODE || mode >= modem_mode::CMUX_MANUAL_MODE) {
             return false;
@@ -191,4 +262,114 @@ modem_mode DCE_Mode::get()
     return mode;
 }
 
+modem_mode DCE_Mode::guess(DTE *dte, bool with_cmux)
+{
+    Scoped<DTE> lock(*dte);
+    return guess_unsafe(dte, with_cmux);
+}
+
+/**
+ * This namespace contains probe packets and expected replies on 3 different protocols,
+ * the modem device could use (as well as timeouts and mode ids for synchronisation)
+ */
+namespace probe {
+
+namespace ppp {
+// Test that we're in the PPP mode by sending an LCP protocol echo request and expecting LCP echo reply
+constexpr std::array<uint8_t, 16> lcp_echo_request = {0x7e, 0xff, 0x03, 0xc0, 0x21, 0x09, 0x01, 0x00, 0x08, 0x99, 0xd1, 0x35, 0xc1, 0x8e, 0x2c, 0x7e };
+constexpr std::array<uint8_t, 5> lcp_echo_reply_head = {0x7e, 0xff, 0x7d, 0x23, 0xc0};
+const size_t mode = 1 << 0;
+const int timeout = 200;
+}
+
+namespace cmd {
+// For command mode, we just send a simple AT command
+const char at[] = "\r\nAT\r\n";
+const size_t max_at_reply = 16; // account for some whitespaces and/or CMUX encapsulation
+const char reply[] = { 'O', 'K' };
+const int mode = 1 << 1;
+const int timeout = 500;
+}
+
+namespace cmux {
+// For CMUX mode, we send an SABM on control terminal (0)
+const uint8_t sabm0_reqest[] = {0xf9, 0x03, 0x3f, 0x01, 0x1c, 0xf9};
+const uint8_t sabm0_reply[] = {0xf9, 0x03, 0x73, 0x01};
+const int mode = 1 << 0;
+const int timeout = 200;
+}
+};
+
+modem_mode DCE_Mode::guess_unsafe(DTE *dte, bool with_cmux)
+{
+    // placeholder for reply and its size, since it could come in pieces, and we have to cache
+    // this is captured by the lambda by reference.
+    // must make sure the lambda is cleared before exiting this function (done by dte->on_read(nullptr))
+    uint8_t reply[std::max(probe::cmd::max_at_reply, std::max(sizeof(probe::ppp::lcp_echo_request), sizeof(probe::cmux::sabm0_reply)))];
+    size_t reply_pos = 0;
+    auto signal = std::make_shared<SignalGroup>();
+    std::weak_ptr<SignalGroup> weak_signal = signal;
+    dte->on_read([weak_signal, with_cmux, &reply, &reply_pos](uint8_t *data, size_t len) {
+        // storing the response in the `reply` array and de-fragmenting
+        if (reply_pos >= sizeof(reply)) {
+            return command_result::TIMEOUT;
+        }
+        auto reply_size = std::min((size_t)sizeof(reply) - reply_pos, len);
+        ::memcpy(reply + reply_pos, data, reply_size);
+        reply_pos += reply_size;
+        ESP_LOG_BUFFER_HEXDUMP("esp-modem: guess mode data:", reply, reply_pos, ESP_LOG_DEBUG);
+
+        // Check whether the response resembles the "golden" reply (for these 3 protocols)
+        if (reply_pos >= sizeof(probe::ppp::lcp_echo_reply_head)) {
+            // check for initial 2 bytes
+            auto *ptr = static_cast<uint8_t *>(memmem(reply, reply_pos, probe::ppp::lcp_echo_reply_head.data(), 2));
+            // and check the other two bytes for protocol ID: LCP
+            if (ptr && ptr[3] == probe::ppp::lcp_echo_reply_head[3] && ptr[4] == probe::ppp::lcp_echo_reply_head[4]) {
+                if (auto signal = weak_signal.lock()) {
+                    signal->set(probe::ppp::mode);
+                }
+            }
+        }
+        if (reply_pos >= 4 && memmem(reply, reply_pos, probe::cmd::reply, sizeof(probe::cmd::reply))) {
+            if (reply[0] != 0xf9) {   // double check that the reply is not wrapped in CMUX headers
+                if (auto signal = weak_signal.lock()) {
+                    signal->set(probe::cmd::mode);
+                }
+            }
+        }
+        if (with_cmux && reply_pos >= sizeof(probe::cmux::sabm0_reply)) {
+            // checking the initial 3 bytes
+            auto *ptr = static_cast<uint8_t *>(memmem(reply, reply_pos, probe::cmux::sabm0_reply, 3));
+            // and checking that DLCI is 0 (control frame)
+            if (ptr && (ptr[3] >> 2) == 0) {
+                if (auto signal = weak_signal.lock()) {
+                    signal->set(probe::cmux::mode);
+                }
+            }
+        }
+        return command_result::TIMEOUT;
+    });
+    auto guessed = modem_mode::UNDEF;
+    // Check the PPP mode fist by sending LCP echo request
+    dte->send((uint8_t *)probe::ppp::lcp_echo_request.data(), sizeof(probe::ppp::lcp_echo_request), 0);
+    if (signal->wait(probe::ppp::mode, probe::ppp::timeout)) {
+        guessed = modem_mode::DATA_MODE;
+    } else {    // LCP echo timeout
+        // now check for AT mode
+        reply_pos = 0;
+        dte->send((uint8_t *)probe::cmd::at, sizeof(probe::cmd::at), 0);
+        if (signal->wait(probe::cmd::mode, probe::cmd::timeout)) {
+            guessed = modem_mode::COMMAND_MODE;
+        } else if (with_cmux) {     // no AT reply, check for CMUX mode (if requested)
+            reply_pos = 0;
+            dte->send((uint8_t *) probe::cmux::sabm0_reqest, sizeof(probe::cmux::sabm0_reqest), 0);
+            if (signal->wait(probe::cmux::mode, probe::cmux::timeout)) {
+                guessed = modem_mode::CMUX_MODE;
+            }
+        }
+    }
+    dte->on_read(nullptr);
+    return guessed;
+}
+
 } // esp_modem

components/esp_modem/src/esp_modem_dte.cpp

@@ -223,13 +223,13 @@ bool DTE::set_mode(modem_mode m)
         }
     }
     // transitions (COMMAND|DUAL|CMUX|UNDEF) -> DATA
-    if (m == modem_mode::DATA_MODE) {
+    if (m == modem_mode::DATA_MODE || m == modem_mode::RESUME_DATA_MODE) {
         if (mode == modem_mode::CMUX_MODE || mode == modem_mode::CMUX_MANUAL_MODE || mode == modem_mode::DUAL_MODE) {
             // mode stays the same, but need to swap terminals (as command has been switched)
             secondary_term.swap(primary_term);
             set_command_callbacks();
         } else {
-            mode = m;
+            mode = modem_mode::DATA_MODE;
         }
         return true;
     }
@@ -316,6 +316,12 @@ int DTE::write(uint8_t *data, size_t len)
     return secondary_term->write(data, len);
 }
 
+int DTE::send(uint8_t *data, size_t len, int term_id)
+{
+    Terminal *term = term_id == 0 ? primary_term.get() : secondary_term.get();
+    return term->write(data, len);
+}
+
 int DTE::write(DTE_Command command)
 {
     return primary_term->write(command.data, command.len);

components/esp_modem/src/esp_modem_netif.cpp

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2021-2024 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -87,8 +87,10 @@ void Netif::start()
         receive(data, len);
         return true;
     });
-    signal.set(PPP_STARTED);
-    esp_netif_action_start(driver.base.netif, nullptr, 0, nullptr);
+    if (!signal.is_any(PPP_STARTED)) {
+        signal.set(PPP_STARTED);
+        esp_netif_action_start(driver.base.netif, nullptr, 0, nullptr);
+    }
 }
 
 void Netif::stop()