#include <STM32FreeRTOS.h>

SemaphoreHandle_t mutex;
const bool USE_MUTEX = true;   // <-- flip to true to fix it, then re-run

// Print a sequence one character at a time, yielding between each char
// so the scheduler can switch mid-sequence.
void printSeq(const char *seq) {
  if (USE_MUTEX) xSemaphoreTake(mutex, portMAX_DELAY);

  for (int i = 0; seq[i] != '\0'; i++) {
    Serial.print(seq[i]);
    vTaskDelay(pdMS_TO_TICKS(2));   // hand off mid-sequence
  }
  Serial.println();

  if (USE_MUTEX) xSemaphoreGive(mutex);
}

void taskA(void *pv) {
  for (;;) { printSeq("abcdefg"); vTaskDelay(pdMS_TO_TICKS(20)); }
}

void taskB(void *pv) {
  for (;;) { printSeq("1234567"); vTaskDelay(pdMS_TO_TICKS(20)); }
}

void setup() {
  Serial.begin(115200);
  mutex = xSemaphoreCreateMutex();
  xTaskCreate(taskA, "A", 256, NULL, 1, NULL);
  xTaskCreate(taskB, "B", 256, NULL, 1, NULL);
  vTaskStartScheduler();
}

void loop() {}