Embedded Systems & RTOS test (Intermediate)

Sample questions

5 sample questions from the Embedded Systems & RTOS test, with the answers. Samples are taken out of the live test, so you will not meet these when you sit it.

1. Consider the following Embedded C code: `#define GPIOA_ODR (*(volatile uint32_t *)0x40020014u)`. Which of the following statements best describes the problem with this code?

   1. The code is correct because the address is an example and does not need to be verified.
   2. The code is incorrect because the address 0x40020014 is not valid for any MCU peripheral.
   3. The code is correct because memory-mapped I/O addresses are always 0x40020014 on Cortex-M devices.
   4. The code is incorrect because the address 0x40020014 is not a valid memory-mapped I/O address for any peripheral on the Cortex-M architecture.

   Answer: D. The code is incorrect because the address 0x40020014 is not a valid memory-mapped I/O address for any peripheral on the Cortex-M architecture.

   In Cortex-M microcontrollers, memory-mapped I/O addresses are specific to the MCU family and peripherals. The address 0x40020014 is an example provided in the notes but does not correspond to a real memory-mapped I/O address. The actual address depends on the specific MCU being used, and assuming it is valid without verifying the datasheet would lead to incorrect register access and potential system malfunctions.

2. What happens when a task calls a queue receive function with a timeout parameter in an RTOS?

   1. The task will continue executing without waiting for a message.
   2. The task will restart the timeout after each system tick.
   3. The task will immediately return with an error if no message is available.
   4. The task will block until a message is received or the timeout expires.

   Answer: D. The task will block until a message is received or the timeout expires.

   In an RTOS, when a task calls a queue receive function with a timeout, it will block (wait) until a message is available or the specified timeout period has elapsed. This behavior allows the task to wait for data without consuming excessive CPU resources.

3. Which of the following statements best describes a key advantage of using message queues for RTOS task communication?

   1. Message queues allow tasks to pass data without requiring direct synchronization, reducing complexity and improving modularity.
   2. Message queues are not supported in FreeRTOS and must be implemented manually.
   3. Message queues are limited to passing pointers and require manual memory management.
   4. Message queues can only be used between tasks of equal priority.

   Answer: A. Message queues allow tasks to pass data without requiring direct synchronization, reducing complexity and improving modularity.

   Message queues are a key RTOS mechanism for task communication. They allow tasks to pass data asynchronously, which enhances modularity and reduces complexity compared to direct synchronization mechanisms like semaphores or mutexes. Options 1, 2, and 3 either describe incorrect behaviors or are unrelated to message queues.

4. In an embedded system using FreeRTOS, how should two tasks communicate via a message queue to ensure efficient and safe data transfer?

   1. The receiving task polls the queue periodically to check for new messages.
   2. The sending task waits for the receiving task to be ready before sending the message.
   3. The task sends a message to the queue, and the receiving task processes it when it becomes ready.
   4. The message is stored in shared memory and accessed directly by both tasks.

   Answer: C. The task sends a message to the queue, and the receiving task processes it when it becomes ready.

   In an RTOS, tasks can communicate via message queues by sending and receiving messages. The sending task places data in the queue, and the receiving task retrieves it when it is ready to process it. This ensures that tasks can exchange data asynchronously and safely without direct dependency on each other's execution timing.

5. Which of the following best describes the configuration of RTOS task stack size and heap memory?

   1. RTOS task stack size is configured during task creation, and it is typically set to a fixed size based on the task's requirements, while heap memory is dynamically allocated and managed by the system.
   2. RTOS task stack size is configured during task creation, and it is typically set to a fixed size based on the task's requirements, while heap memory is also set to a fixed size based on the task's requirements.
   3. RTOS task stack size is dynamically allocated and managed by the system, while heap memory is configured during task creation and set to a fixed size based on the task's requirements.
   4. RTOS task stack size is dynamically allocated and managed by the system, while heap memory is also dynamically allocated and managed by the system.

   Answer: A. RTOS task stack size is configured during task creation, and it is typically set to a fixed size based on the task's requirements, while heap memory is dynamically allocated and managed by the system.

   RTOS task stack size is configured during task creation, and it is typically set to a fixed size based on the task's requirements, while heap memory is dynamically allocated and managed by the system. This ensures that each task has enough stack space to operate without interference from other tasks, and the stack size is determined based on the task's needs. Heap memory, on the other hand, is used for dynamic memory allocation and is managed by the system, making it more flexible but potentially less predictable in terms of performance.