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Introduce L2CAP infrastructure.
L2CAP is the underlying technology powering GATT. BLE 5 exposes L2CAP COC (Connection Oriented Channels) allowing a streaming API that leads to much higher throughputs than you can achieve with updating GATT characteristics. The patch follows the established infrastructure very closely. The main components are: - `NimBLEL2CAPChannel`, encapsulating an L2CAP COC. - `NimBLEL2CAPServer`, encapsulating the L2CAP service. - `Examples/L2CAP`, containing a client and a server application. Apart from these, only minor adjustments to the existing code was necessary.
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‎CMakeLists.txt

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"src/NimBLEEddystoneTLM.cpp"
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"src/NimBLEExtAdvertising.cpp"
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"src/NimBLEHIDDevice.cpp"
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"src/NimBLEL2CAPChannel.cpp"
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"src/NimBLEL2CAPServer.cpp"
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"src/NimBLERemoteCharacteristic.cpp"
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"src/NimBLERemoteDescriptor.cpp"
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"src/NimBLERemoteService.cpp"

‎examples/L2CAP/.gitignore

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.vscode
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build
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sdkconfig
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sdkconfig.old
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dependencies.lock

‎examples/L2CAP/L2CAP_Client/CMakeLists.txt

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# The following lines of boilerplate have to be in your project's
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# CMakeLists in this exact order for cmake to work correctly
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cmake_minimum_required(VERSION 3.5)
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include($ENV{IDF_PATH}/tools/cmake/project.cmake)
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set(SUPPORTED_TARGETS esp32 esp32s3 esp32c3 esp32c6)
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project(L2CAP_client)

‎examples/L2CAP/L2CAP_Client/Makefile

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PROJECT_NAME := L2CAP_client
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include $(IDF_PATH)/make/project.mk

‎examples/L2CAP/L2CAP_Client/main/CMakeLists.txt

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set(COMPONENT_SRCS "main.cpp")
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set(COMPONENT_ADD_INCLUDEDIRS ".")
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register_component()

‎examples/L2CAP/L2CAP_Client/main/component.mk

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#
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# "main" pseudo-component makefile.
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#
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# (Uses default behaviour of compiling all source files in directory, adding 'include' to include path.)

‎examples/L2CAP/L2CAP_Client/main/idf_component.yml

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dependencies:
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local/esp-nimble-cpp:
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path: ../../../../../esp-nimble-cpp/

‎examples/L2CAP/L2CAP_Client/main/main.cpp

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#include <NimBLEDevice.h>
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// See the following for generating UUIDs:
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// https://www.uuidgenerator.net/
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// The remote service we wish to connect to.
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static BLEUUID serviceUUID("dcbc7255-1e9e-49a0-a360-b0430b6c6905");
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// The characteristic of the remote service we are interested in.
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static BLEUUID charUUID("371a55c8-f251-4ad2-90b3-c7c195b049be");
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#define L2CAP_CHANNEL 150
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#define L2CAP_MTU 5000
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const BLEAdvertisedDevice* theDevice = NULL;
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BLEClient* theClient = NULL;
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BLEL2CAPChannel* theChannel = NULL;
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size_t bytesSent = 0;
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size_t bytesReceived = 0;
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class L2CAPChannelCallbacks: public BLEL2CAPChannelCallbacks {
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public:
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void onConnect(NimBLEL2CAPChannel* channel) {
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printf("L2CAP connection established\n");
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}
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void onMTUChange(NimBLEL2CAPChannel* channel, uint16_t mtu) {
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printf("L2CAP MTU changed to %d\n", mtu);
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}
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void onRead(NimBLEL2CAPChannel* channel, std::vector<uint8_t>& data) {
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printf("L2CAP read %d bytes\n", data.size());
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}
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void onDisconnect(NimBLEL2CAPChannel* channel) {
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printf("L2CAP disconnected\n");
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}
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};
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class MyClientCallbacks: public BLEClientCallbacks {
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void onConnect(BLEClient* pClient) {
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printf("GAP connected\n");
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pClient->setDataLen(251);
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theChannel = BLEL2CAPChannel::connect(pClient, L2CAP_CHANNEL, L2CAP_MTU, new L2CAPChannelCallbacks());
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}
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void onDisconnect(BLEClient* pClient, int reason) {
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printf("GAP disconnected (reason: %d)\n", reason);
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theDevice = NULL;
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theChannel = NULL;
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vTaskDelay(1000 / portTICK_PERIOD_MS);
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BLEDevice::getScan()->start(5 * 1000, true);
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}
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};
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class MyAdvertisedDeviceCallbacks: public BLEAdvertisedDeviceCallbacks {
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void onResult(const BLEAdvertisedDevice* advertisedDevice) {
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if (theDevice) { return; }
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printf("BLE Advertised Device found: %s\n", advertisedDevice->toString().c_str());
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if (!advertisedDevice->haveServiceUUID()) { return; }
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if (!advertisedDevice->isAdvertisingService(serviceUUID)) { return; }
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printf("Found the device we're interested in!\n");
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BLEDevice::getScan()->stop();
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// Hand over the device to the other task
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theDevice = advertisedDevice;
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}
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};
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void connectTask(void *pvParameters) {
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uint8_t sequenceNumber = 0;
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while (true) {
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if (!theDevice) {
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vTaskDelay(1000 / portTICK_PERIOD_MS);
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continue;
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}
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if (!theClient) {
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theClient = BLEDevice::createClient();
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theClient->setConnectionParams(6, 6, 0, 42);
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auto callbacks = new MyClientCallbacks();
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theClient->setClientCallbacks(callbacks);
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auto success = theClient->connect(theDevice);
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if (!success) {
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printf("Error: Could not connect to device\n");
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break;
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}
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vTaskDelay(2000 / portTICK_PERIOD_MS);
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continue;
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}
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if (!theChannel) {
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printf("l2cap channel not initialized\n");
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vTaskDelay(2000 / portTICK_PERIOD_MS);
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continue;
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}
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if (!theChannel->isConnected()) {
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printf("l2cap channel not connected\n");
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vTaskDelay(2000 / portTICK_PERIOD_MS);
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continue;
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}
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while (theChannel->isConnected()) {
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/*
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static auto initialDelay = true;
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if (initialDelay) {
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printf("Waiting gracefully 3 seconds before sending data\n");
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vTaskDelay(3000 / portTICK_PERIOD_MS);
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initialDelay = false;
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};
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*/
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std::vector<uint8_t> data(5000, sequenceNumber++);
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if (theChannel->write(data)) {
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bytesSent += data.size();
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} else {
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printf("failed to send!\n");
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abort();
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}
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}
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vTaskDelay(1000 / portTICK_PERIOD_MS);
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}
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}
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extern "C"
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void app_main(void) {
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printf("Starting L2CAP client example\n");
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xTaskCreate(connectTask, "connectTask", 5000, NULL, 1, NULL);
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BLEDevice::init("L2CAP-Client");
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BLEDevice::setMTU(BLE_ATT_MTU_MAX);
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auto scan = BLEDevice::getScan();
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auto callbacks = new MyAdvertisedDeviceCallbacks();
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scan->setScanCallbacks(callbacks);
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scan->setInterval(1349);
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scan->setWindow(449);
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scan->setActiveScan(true);
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scan->start(25 * 1000, false);
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int numberOfSeconds = 0;
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while (bytesSent == 0) {
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vTaskDelay(10 / portTICK_PERIOD_MS);
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}
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while (true) {
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vTaskDelay(1000 / portTICK_PERIOD_MS);
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int bytesSentPerSeconds = bytesSent / ++numberOfSeconds;
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printf("Bandwidth: %d b/sec = %d KB/sec\n", bytesSentPerSeconds, bytesSentPerSeconds / 1024);
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}
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}

‎examples/L2CAP/L2CAP_Client/sdkconfig.defaults

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# Override some defaults so BT stack is enabled
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# in this example
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#
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# BT config
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#
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CONFIG_BT_ENABLED=y
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CONFIG_BTDM_CTRL_MODE_BLE_ONLY=y
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CONFIG_BTDM_CTRL_MODE_BR_EDR_ONLY=n
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CONFIG_BTDM_CTRL_MODE_BTDM=n
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CONFIG_BT_BLUEDROID_ENABLED=n
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CONFIG_BT_NIMBLE_ENABLED=y
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CONFIG_BT_NIMBLE_L2CAP_COC_MAX_NUM=1

‎examples/L2CAP/L2CAP_Server/CMakeLists.txt

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# The following lines of boilerplate have to be in your project's
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# CMakeLists in this exact order for cmake to work correctly
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cmake_minimum_required(VERSION 3.5)
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include($ENV{IDF_PATH}/tools/cmake/project.cmake)
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set(SUPPORTED_TARGETS esp32 esp32s3 esp32c3 esp32c6)
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project(L2CAP_server)

‎examples/L2CAP/L2CAP_Server/Makefile

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PROJECT_NAME := L2CAP_server
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include $(IDF_PATH)/make/project.mk

‎examples/L2CAP/L2CAP_Server/main/CMakeLists.txt

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set(COMPONENT_SRCS "main.cpp")
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set(COMPONENT_ADD_INCLUDEDIRS ".")
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register_component()

‎examples/L2CAP/L2CAP_Server/main/component.mk

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#
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# "main" pseudo-component makefile.
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#
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# (Uses default behaviour of compiling all source files in directory, adding 'include' to include path.)

‎examples/L2CAP/L2CAP_Server/main/idf_component.yml

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dependencies:
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local/esp-nimble-cpp:
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path: ../../../../../esp-nimble-cpp/

‎examples/L2CAP/L2CAP_Server/main/main.cpp

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#include <NimBLEDevice.h>
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// See the following for generating UUIDs:
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// https://www.uuidgenerator.net/
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#define SERVICE_UUID "dcbc7255-1e9e-49a0-a360-b0430b6c6905"
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#define CHARACTERISTIC_UUID "371a55c8-f251-4ad2-90b3-c7c195b049be"
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#define L2CAP_CHANNEL 150
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#define L2CAP_MTU 5000
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class GATTCallbacks: public BLEServerCallbacks {
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public:
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void onConnect(BLEServer* pServer, BLEConnInfo& info) {
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/// Booster #1
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pServer->setDataLen(info.getConnHandle(), 251);
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/// Booster #2 (especially for Apple devices)
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BLEDevice::getServer()->updateConnParams(info.getConnHandle(), 12, 12, 0, 200);
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}
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};
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class L2CAPChannelCallbacks: public BLEL2CAPChannelCallbacks {
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public:
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bool connected = false;
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size_t numberOfReceivedBytes;
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uint8_t nextSequenceNumber;
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public:
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void onConnect(NimBLEL2CAPChannel* channel) {
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printf("L2CAP connection established\n");
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connected = true;
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numberOfReceivedBytes = nextSequenceNumber = 0;
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}
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void onRead(NimBLEL2CAPChannel* channel, std::vector<uint8_t>& data) {
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numberOfReceivedBytes += data.size();
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size_t sequenceNumber = data[0];
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printf("L2CAP read %d bytes w/ sequence number %d", data.size(), sequenceNumber);
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if (sequenceNumber != nextSequenceNumber) {
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printf("(wrong sequence number %d, expected %d)\n", sequenceNumber, nextSequenceNumber);
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} else {
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printf("\n");
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nextSequenceNumber++;
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}
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}
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void onDisconnect(NimBLEL2CAPChannel* channel) {
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printf("L2CAP disconnected\n");
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connected = false;
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}
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};
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extern "C"
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void app_main(void) {
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printf("Starting L2CAP server example [%lu free] [%lu min]\n", esp_get_free_heap_size(), esp_get_minimum_free_heap_size());
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BLEDevice::init("L2CAP-Server");
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BLEDevice::setMTU(BLE_ATT_MTU_MAX);
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auto cocServer = BLEDevice::createL2CAPServer();
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auto l2capChannelCallbacks = new L2CAPChannelCallbacks();
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auto channel = cocServer->createService(L2CAP_CHANNEL, L2CAP_MTU, l2capChannelCallbacks);
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auto server = BLEDevice::createServer();
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server->setCallbacks(new GATTCallbacks());
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auto service = server->createService(SERVICE_UUID);
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auto characteristic = service->createCharacteristic(CHARACTERISTIC_UUID, NIMBLE_PROPERTY::READ);
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characteristic->setValue(L2CAP_CHANNEL);
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service->start();
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auto advertising = BLEDevice::getAdvertising();
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advertising->addServiceUUID(SERVICE_UUID);
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advertising->enableScanResponse(true);
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BLEDevice::startAdvertising();
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printf("Server waiting for connection requests [%lu free] [%lu min]\n", esp_get_free_heap_size(), esp_get_minimum_free_heap_size());
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// Wait until transfer actually starts...
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while (!l2capChannelCallbacks->numberOfReceivedBytes) {
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vTaskDelay(10 / portTICK_PERIOD_MS);
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}
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printf("\n\n\n");
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int numberOfSeconds = 0;
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while (true) {
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vTaskDelay(1000 / portTICK_PERIOD_MS);
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if (!l2capChannelCallbacks->connected) { continue; }
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int bps = l2capChannelCallbacks->numberOfReceivedBytes / ++numberOfSeconds;
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printf("Bandwidth: %d b/sec = %d KB/sec [%lu free] [%lu min]\n", bps, bps / 1024, esp_get_free_heap_size(), esp_get_minimum_free_heap_size());
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}
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}

‎examples/L2CAP/L2CAP_Server/sdkconfig.defaults

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# Override some defaults so BT stack is enabled
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# in this example
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#
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# BT config
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#
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CONFIG_BT_ENABLED=y
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CONFIG_BTDM_CTRL_MODE_BLE_ONLY=y
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CONFIG_BTDM_CTRL_MODE_BR_EDR_ONLY=n
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CONFIG_BTDM_CTRL_MODE_BTDM=n
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CONFIG_BT_BLUEDROID_ENABLED=n
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CONFIG_BT_NIMBLE_ENABLED=y
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CONFIG_BT_NIMBLE_L2CAP_COC_MAX_NUM=1

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