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{"@context":"https://schema.org","@type":"QAPage","mainEntity":{"@type":"Question","name":"Problems with xMessageBufferReceive.","text":"\u003cp dir=\"auto\"\u003eAs a pedagogical exercise, I wrote an app with one task that blink a led and push some string in a Message buffer. (task1)\u003cbr\u003e\nMessages from the Message Buffer are sent over serial from another task (task2).\u003cbr\u003e\nI further used a binary semaphore and a mutex for regulating the access to the Message Buffer and the Serial.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003eMy problem is that everything get stuck when I use xMessageBufferReceive().\u003cbr\u003e\nBelow a reproducible code, where I marked the non working part.\u003cbr\u003e\nIf you comment that section and uncomment e.g. the line above ( /* Serial.println(\"TEST\"); */) you will see that everything works.\u003cbr\u003e\nWhat I am doing wrong?\u003c/p\u003e\n\u003cdiv class=\"snippet-clipboard-content notranslate position-relative overflow-auto\" data-snippet-clipboard-copy-content=\"#include \u0026quot;FreeRTOSVariant.h\u0026quot;\n#include \u0026quot;HardwareSerial.h\u0026quot;\n#include \u0026quot;portable.h\u0026quot;\n#include \u0026quot;projdefs.h\u0026quot;\n#include \u0026lt;Arduino.h\u0026gt;\n#include \u0026lt;message_buffer.h\u0026gt;\n#include \u0026lt;semphr.h\u0026gt;\n\n// Global variables: semaphore and message buffer\n/* Create a message buffer to send data to the serial*/\nconst size_t MESSAGE_SIZE = 100;\nMessageBufferHandle_t xMessageBuffer = xMessageBufferCreate(MESSAGE_SIZE);\n\n/* Create a semaphore to control access to the message buffer */\n// TODO: do we really need static?\nstatic SemaphoreHandle_t xSemaphoreMessageBuffer = xSemaphoreCreateBinary();\nstatic SemaphoreHandle_t xSemaphoreSerialPort = xSemaphoreCreateMutex();\n\n// Task functions prototypes\nvoid task_blink(void *pVParameters);\nvoid task_serial(void *pVParameters);\n\nvoid setup() {\n\n  // initialize serial communication at 9600 bits per second:\n  const unsigned int BAUDRATE = 9600;\n  Serial.begin(BAUDRATE);\n\n  // TODO: is it really needed?\n  while (!Serial) {\n    ; // wait for serial port to connect. Needed for native USB, on LEONARDO,\n  }\n\n  // Release all the semaphore at the very beginning.\n  xSemaphoreGive(xSemaphoreMessageBuffer);\n  xSemaphoreGive(xSemaphoreSerialPort);\n\n  // Task: Blink\n  const size_t STACK_SIZE_BLINK = 128;\n  const uint8_t PRIORITY_BLINK = 2;\n  TaskHandle_t xTaskHandleBlink;\n\n  xTaskCreate(task_blink, \u0026quot;Blink\u0026quot;, STACK_SIZE_BLINK, NULL, PRIORITY_BLINK,\n              \u0026amp;xTaskHandleBlink);\n\n  // Task: Serial\n  const size_t STACK_SIZE_SERIAL = 128;\n  const uint8_t PRIORITY_SERIAL = 2;\n  TaskHandle_t xTaskHandleSerial;\n\n  xTaskCreate(task_serial, \u0026quot;Serial\u0026quot;, STACK_SIZE_SERIAL, NULL, PRIORITY_SERIAL,\n              \u0026amp;xTaskHandleSerial);\n}\n// Skip loop. OBS! IdleTask cannot be used!\nvoid loop() {}\n\n// Task implementation\nvoid task_blink(void *pVParameters) // This is a task.\n{\n  (void)pVParameters;\n  const int TASK_PERIOD = 1000;\n\n  // initialize digital LED_BUILTIN on pin 13 as an output.\n  pinMode(LED_BUILTIN, OUTPUT);\n  static uint8_t counter = 0;\n  const size_t MAX_COUNT = 2;\n\n  // Condition for sending a message over the serial port\n  boolean isMessageBufferSemaphoreTaken;\n  boolean isMessageShortEnough;\n\n  while (true) {\n    static bool led_state = false;\n    // send something every MAX_COUNT*TASK_PERIOD seconds.\n\n    if (!led_state) {\n      digitalWrite(LED_BUILTIN, HIGH);\n      led_state = true;\n    } else {\n      digitalWrite(LED_BUILTIN, LOW);\n      led_state = false;\n    }\n\n    char message[] = \u0026quot;dog\u0026quot;;\n    if (counter == MAX_COUNT) {\n\n      // Debug\n      /* Serial.print(\u0026quot;Available space in message buffer: \u0026quot;); */\n      /* Serial.println(xMessageBufferSpacesAvailable((xMessageBuffer))); */\n\n      // Check if you can send a message\n      isMessageBufferSemaphoreTaken =\n          xSemaphoreTake(xSemaphoreMessageBuffer, 1000 / portTICK_PERIOD_MS) ==\n          pdTRUE;\n      isMessageShortEnough =\n          xMessageBufferSpacesAvailable((xMessageBuffer)) \u0026gt; strlen(message);\n\n      if (isMessageBufferSemaphoreTaken \u0026amp;\u0026amp; isMessageShortEnough) {\n        xMessageBufferSend(xMessageBuffer, message, sizeof(message), 0);\n        /* Serial.println(\u0026quot;Message sent!\u0026quot;); */\n        xSemaphoreGive(xSemaphoreMessageBuffer);\n      }\n      counter = 0;\n    } else {\n      counter++;\n    }\n\n    // Task Schedule\n    const TickType_t X_DELAY = TASK_PERIOD / portTICK_PERIOD_MS;\n    vTaskDelay(X_DELAY); // one tick delay (15ms)\n  }\n}\n\nvoid task_serial(void *pVParameters) // This is a task.\n{\n  (void)pVParameters;\n  const uint8_t TASK_PERIOD = 200;\n  uint8_t received_data[MESSAGE_SIZE];\n  size_t received_bytes;\n  received_bytes = 0;\n\n  boolean isMessageBufferSemaphoreTaken;\n  boolean isSerialSemaphoreTaken;\n  boolean isMessageBufferEmpty;\n\n  while (true) {\n    // Conditions for writing on the serial\n\n    isSerialSemaphoreTaken =\n        xSemaphoreTake(xSemaphoreSerialPort, 1000 / portTICK_PERIOD_MS) ==\n        pdTRUE;\n    isMessageBufferSemaphoreTaken =\n        xSemaphoreTake(xSemaphoreMessageBuffer, 1000 / portTICK_PERIOD_MS) ==\n        pdTRUE;\n    isMessageBufferEmpty = xMessageBufferIsEmpty(xMessageBuffer) == pdTRUE;\n\n    if (isSerialSemaphoreTaken) {\n      if (isMessageBufferSemaphoreTaken) {\n        if (!isMessageBufferEmpty) {\n          /* Serial.println(\u0026quot;TEST\u0026quot;); */\n\n          /* ------------- BEGIN NON-WORKING PART!!! -----------*/\n          received_bytes = xMessageBufferReceive(xMessageBuffer, received_data,\n                                                 sizeof(received_data), 0);\n          Serial.println(received_bytes);\n          /* ------------- END NON-WORKING PART!!! -----------*/\n        }\n        xSemaphoreGive(xSemaphoreMessageBuffer);\n        /* Serial.println(\u0026quot;(serial) Semaphore MessageBuffer released.\u0026quot;); */\n      }\n      xSemaphoreGive(xSemaphoreSerialPort);\n      /* Serial.println(\u0026quot;(serial) Semaphore serial port released.\u0026quot;); */\n    }\n\n    // TODO: Task Schedule\n    const TickType_t X_DELAY = TASK_PERIOD / portTICK_PERIOD_MS;\n    vTaskDelay(X_DELAY); // one tick delay (15ms)\n  }\n}\"\u003e\u003cpre class=\"notranslate\"\u003e\u003ccode class=\"notranslate\"\u003e#include \"FreeRTOSVariant.h\"\n#include \"HardwareSerial.h\"\n#include \"portable.h\"\n#include \"projdefs.h\"\n#include \u0026lt;Arduino.h\u0026gt;\n#include \u0026lt;message_buffer.h\u0026gt;\n#include \u0026lt;semphr.h\u0026gt;\n\n// Global variables: semaphore and message buffer\n/* Create a message buffer to send data to the serial*/\nconst size_t MESSAGE_SIZE = 100;\nMessageBufferHandle_t xMessageBuffer = xMessageBufferCreate(MESSAGE_SIZE);\n\n/* Create a semaphore to control access to the message buffer */\n// TODO: do we really need static?\nstatic SemaphoreHandle_t xSemaphoreMessageBuffer = xSemaphoreCreateBinary();\nstatic SemaphoreHandle_t xSemaphoreSerialPort = xSemaphoreCreateMutex();\n\n// Task functions prototypes\nvoid task_blink(void *pVParameters);\nvoid task_serial(void *pVParameters);\n\nvoid setup() {\n\n  // initialize serial communication at 9600 bits per second:\n  const unsigned int BAUDRATE = 9600;\n  Serial.begin(BAUDRATE);\n\n  // TODO: is it really needed?\n  while (!Serial) {\n    ; // wait for serial port to connect. Needed for native USB, on LEONARDO,\n  }\n\n  // Release all the semaphore at the very beginning.\n  xSemaphoreGive(xSemaphoreMessageBuffer);\n  xSemaphoreGive(xSemaphoreSerialPort);\n\n  // Task: Blink\n  const size_t STACK_SIZE_BLINK = 128;\n  const uint8_t PRIORITY_BLINK = 2;\n  TaskHandle_t xTaskHandleBlink;\n\n  xTaskCreate(task_blink, \"Blink\", STACK_SIZE_BLINK, NULL, PRIORITY_BLINK,\n              \u0026amp;xTaskHandleBlink);\n\n  // Task: Serial\n  const size_t STACK_SIZE_SERIAL = 128;\n  const uint8_t PRIORITY_SERIAL = 2;\n  TaskHandle_t xTaskHandleSerial;\n\n  xTaskCreate(task_serial, \"Serial\", STACK_SIZE_SERIAL, NULL, PRIORITY_SERIAL,\n              \u0026amp;xTaskHandleSerial);\n}\n// Skip loop. OBS! IdleTask cannot be used!\nvoid loop() {}\n\n// Task implementation\nvoid task_blink(void *pVParameters) // This is a task.\n{\n  (void)pVParameters;\n  const int TASK_PERIOD = 1000;\n\n  // initialize digital LED_BUILTIN on pin 13 as an output.\n  pinMode(LED_BUILTIN, OUTPUT);\n  static uint8_t counter = 0;\n  const size_t MAX_COUNT = 2;\n\n  // Condition for sending a message over the serial port\n  boolean isMessageBufferSemaphoreTaken;\n  boolean isMessageShortEnough;\n\n  while (true) {\n    static bool led_state = false;\n    // send something every MAX_COUNT*TASK_PERIOD seconds.\n\n    if (!led_state) {\n      digitalWrite(LED_BUILTIN, HIGH);\n      led_state = true;\n    } else {\n      digitalWrite(LED_BUILTIN, LOW);\n      led_state = false;\n    }\n\n    char message[] = \"dog\";\n    if (counter == MAX_COUNT) {\n\n      // Debug\n      /* Serial.print(\"Available space in message buffer: \"); */\n      /* Serial.println(xMessageBufferSpacesAvailable((xMessageBuffer))); */\n\n      // Check if you can send a message\n      isMessageBufferSemaphoreTaken =\n          xSemaphoreTake(xSemaphoreMessageBuffer, 1000 / portTICK_PERIOD_MS) ==\n          pdTRUE;\n      isMessageShortEnough =\n          xMessageBufferSpacesAvailable((xMessageBuffer)) \u0026gt; strlen(message);\n\n      if (isMessageBufferSemaphoreTaken \u0026amp;\u0026amp; isMessageShortEnough) {\n        xMessageBufferSend(xMessageBuffer, message, sizeof(message), 0);\n        /* Serial.println(\"Message sent!\"); */\n        xSemaphoreGive(xSemaphoreMessageBuffer);\n      }\n      counter = 0;\n    } else {\n      counter++;\n    }\n\n    // Task Schedule\n    const TickType_t X_DELAY = TASK_PERIOD / portTICK_PERIOD_MS;\n    vTaskDelay(X_DELAY); // one tick delay (15ms)\n  }\n}\n\nvoid task_serial(void *pVParameters) // This is a task.\n{\n  (void)pVParameters;\n  const uint8_t TASK_PERIOD = 200;\n  uint8_t received_data[MESSAGE_SIZE];\n  size_t received_bytes;\n  received_bytes = 0;\n\n  boolean isMessageBufferSemaphoreTaken;\n  boolean isSerialSemaphoreTaken;\n  boolean isMessageBufferEmpty;\n\n  while (true) {\n    // Conditions for writing on the serial\n\n    isSerialSemaphoreTaken =\n        xSemaphoreTake(xSemaphoreSerialPort, 1000 / portTICK_PERIOD_MS) ==\n        pdTRUE;\n    isMessageBufferSemaphoreTaken =\n        xSemaphoreTake(xSemaphoreMessageBuffer, 1000 / portTICK_PERIOD_MS) ==\n        pdTRUE;\n    isMessageBufferEmpty = xMessageBufferIsEmpty(xMessageBuffer) == pdTRUE;\n\n    if (isSerialSemaphoreTaken) {\n      if (isMessageBufferSemaphoreTaken) {\n        if (!isMessageBufferEmpty) {\n          /* Serial.println(\"TEST\"); */\n\n          /* ------------- BEGIN NON-WORKING PART!!! -----------*/\n          received_bytes = xMessageBufferReceive(xMessageBuffer, received_data,\n                                                 sizeof(received_data), 0);\n          Serial.println(received_bytes);\n          /* ------------- END NON-WORKING PART!!! -----------*/\n        }\n        xSemaphoreGive(xSemaphoreMessageBuffer);\n        /* Serial.println(\"(serial) Semaphore MessageBuffer released.\"); */\n      }\n      xSemaphoreGive(xSemaphoreSerialPort);\n      /* Serial.println(\"(serial) Semaphore serial port released.\"); */\n    }\n\n    // TODO: Task Schedule\n    const TickType_t X_DELAY = TASK_PERIOD / portTICK_PERIOD_MS;\n    vTaskDelay(X_DELAY); // one tick delay (15ms)\n  }\n}\n\u003c/code\u003e\u003c/pre\u003e\u003c/div\u003e","upvoteCount":1,"answerCount":4,"acceptedAnswer":{"@type":"Answer","text":"\u003cp dir=\"auto\"\u003eWithout looking in detail, using \u003ccode class=\"notranslate\"\u003eSerial.println()\u003c/code\u003e is an Arduino C++ trap. Expect to need over 512 bytes of stack to instantiate that class of functions, IIRC, and 128 bytes is nowhere near sufficient. Check other past issues here for more details.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003ePerhaps test and report if you could, please. Then we can look in more detail.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003eThere's a low level print function available as an option, IIRC.\u003c/p\u003e","upvoteCount":1,"url":"https://github.com/feilipu/Arduino_FreeRTOS_Library/discussions/128#discussioncomment-8029867"}}}