RTOS interview questions

1. A.mutex protocol raising the holder to the priority of the highest waiter so it finishes quickly; FreeRTOS mutexes implement it, binary semaphores do not
2. B.each task owns a stack and a priority, and the scheduler runs the highest-priority ready task, switching pre-emptively on interrupts or the tick
3. C.semaphore signals events or counts resources and may be given from an ISR; mutex protects a shared resource, has an owner and supports priority inheritance
4. D.functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined

Answer + AI explanation with Pro

1. A.Task and scheduler
2. B.Tick rate
3. C.Queue
4. D.Zephyr RTOS

Answer + AI explanation with Pro

1. A.Task and scheduler — Linux Foundation real-time OS with device-tree hardware description, Kconfig configuration, the west build tool and native Bluetooth, networking and MCUboot support
2. B.Task and scheduler — periodic timer interrupt, commonly 1 kHz via configTICK_RATE_HZ, driving time slicing, delays and timeouts, with tickless idle available to save power
3. C.Task and scheduler — choose task stacks from high-water-mark measurement with margin for worst-case call depth and ISR nesting, enabling overflow check hooks during development
4. D.Task and scheduler — each task owns a stack and a priority, and the scheduler runs the highest-priority ready task, switching pre-emptively on interrupts or the tick

Answer + AI explanation with Pro

1. A.semaphore signals events or counts resources and may be given from an ISR; mutex protects a shared resource, has an owner and supports priority inheritance
2. B.choose task stacks from high-water-mark measurement with margin for worst-case call depth and ISR nesting, enabling overflow check hooks during development
3. C.functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined
4. D.Linux Foundation real-time OS with device-tree hardware description, Kconfig configuration, the west build tool and native Bluetooth, networking and MCUboot support

Answer + AI explanation with Pro

1. A.Stack sizing
2. B.Semaphore versus mutex
3. C.Zephyr RTOS
4. D.Task and scheduler

Answer + AI explanation with Pro

1. A.Semaphore versus mutex — a high-priority task blocked on a mutex held by a low-priority task that is itself pre-empted by medium-priority tasks, the failure behind the Mars Pathfinder resets
2. B.Semaphore versus mutex — Linux Foundation real-time OS with device-tree hardware description, Kconfig configuration, the west build tool and native Bluetooth, networking and MCUboot support
3. C.Semaphore versus mutex — semaphore signals events or counts resources and may be given from an ISR; mutex protects a shared resource, has an owner and supports priority inheritance
4. D.Semaphore versus mutex — each task owns a stack and a priority, and the scheduler runs the highest-priority ready task, switching pre-emptively on interrupts or the tick

Answer + AI explanation with Pro

1. A.periodic timer interrupt, commonly 1 kHz via configTICK_RATE_HZ, driving time slicing, delays and timeouts, with tickless idle available to save power
2. B.Linux Foundation real-time OS with device-tree hardware description, Kconfig configuration, the west build tool and native Bluetooth, networking and MCUboot support
3. C.mutex protocol raising the holder to the priority of the highest waiter so it finishes quickly; FreeRTOS mutexes implement it, binary semaphores do not
4. D.each task owns a stack and a priority, and the scheduler runs the highest-priority ready task, switching pre-emptively on interrupts or the tick

Answer + AI explanation with Pro

1. A.Priority inheritance
2. B.Tick rate
3. C.ISR-safe APIs
4. D.Zephyr RTOS

Answer + AI explanation with Pro

1. A.Tick rate — functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined
2. B.Tick rate — semaphore signals events or counts resources and may be given from an ISR; mutex protects a shared resource, has an owner and supports priority inheritance
3. C.Tick rate — thread-safe FIFO copying items by value between tasks or from ISRs, with blocking send and receive plus timeouts, the recommended way to pass data out of interrupts
4. D.Tick rate — periodic timer interrupt, commonly 1 kHz via configTICK_RATE_HZ, driving time slicing, delays and timeouts, with tickless idle available to save power

Answer + AI explanation with Pro

1. A.semaphore signals events or counts resources and may be given from an ISR; mutex protects a shared resource, has an owner and supports priority inheritance
2. B.a high-priority task blocked on a mutex held by a low-priority task that is itself pre-empted by medium-priority tasks, the failure behind the Mars Pathfinder resets
3. C.functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined
4. D.choose task stacks from high-water-mark measurement with margin for worst-case call depth and ISR nesting, enabling overflow check hooks during development

Answer + AI explanation with Pro

1. A.Task and scheduler
2. B.Tick rate
3. C.Queue
4. D.Priority inversion

Answer + AI explanation with Pro

1. A.Priority inversion — thread-safe FIFO copying items by value between tasks or from ISRs, with blocking send and receive plus timeouts, the recommended way to pass data out of interrupts
2. B.Priority inversion — mutex protocol raising the holder to the priority of the highest waiter so it finishes quickly; FreeRTOS mutexes implement it, binary semaphores do not
3. C.Priority inversion — semaphore signals events or counts resources and may be given from an ISR; mutex protects a shared resource, has an owner and supports priority inheritance
4. D.Priority inversion — a high-priority task blocked on a mutex held by a low-priority task that is itself pre-empted by medium-priority tasks, the failure behind the Mars Pathfinder resets

Answer + AI explanation with Pro

1. A.each task owns a stack and a priority, and the scheduler runs the highest-priority ready task, switching pre-emptively on interrupts or the tick
2. B.choose task stacks from high-water-mark measurement with margin for worst-case call depth and ISR nesting, enabling overflow check hooks during development
3. C.semaphore signals events or counts resources and may be given from an ISR; mutex protects a shared resource, has an owner and supports priority inheritance
4. D.mutex protocol raising the holder to the priority of the highest waiter so it finishes quickly; FreeRTOS mutexes implement it, binary semaphores do not

Answer + AI explanation with Pro

1. A.Priority inheritance
2. B.Zephyr RTOS
3. C.Stack sizing
4. D.Tick rate

Answer + AI explanation with Pro

1. A.Priority inheritance — a high-priority task blocked on a mutex held by a low-priority task that is itself pre-empted by medium-priority tasks, the failure behind the Mars Pathfinder resets
2. B.Priority inheritance — functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined
3. C.Priority inheritance — thread-safe FIFO copying items by value between tasks or from ISRs, with blocking send and receive plus timeouts, the recommended way to pass data out of interrupts
4. D.Priority inheritance — mutex protocol raising the holder to the priority of the highest waiter so it finishes quickly; FreeRTOS mutexes implement it, binary semaphores do not

Answer + AI explanation with Pro

1. A.semaphore signals events or counts resources and may be given from an ISR; mutex protects a shared resource, has an owner and supports priority inheritance
2. B.a high-priority task blocked on a mutex held by a low-priority task that is itself pre-empted by medium-priority tasks, the failure behind the Mars Pathfinder resets
3. C.functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined
4. D.thread-safe FIFO copying items by value between tasks or from ISRs, with blocking send and receive plus timeouts, the recommended way to pass data out of interrupts

Answer + AI explanation with Pro

1. A.Zephyr RTOS
2. B.ISR-safe APIs
3. C.Priority inversion
4. D.Queue

Answer + AI explanation with Pro

1. A.Queue — functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined
2. B.Queue — a high-priority task blocked on a mutex held by a low-priority task that is itself pre-empted by medium-priority tasks, the failure behind the Mars Pathfinder resets
3. C.Queue — periodic timer interrupt, commonly 1 kHz via configTICK_RATE_HZ, driving time slicing, delays and timeouts, with tickless idle available to save power
4. D.Queue — thread-safe FIFO copying items by value between tasks or from ISRs, with blocking send and receive plus timeouts, the recommended way to pass data out of interrupts

Answer + AI explanation with Pro

1. A.semaphore signals events or counts resources and may be given from an ISR; mutex protects a shared resource, has an owner and supports priority inheritance
2. B.functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined
3. C.choose task stacks from high-water-mark measurement with margin for worst-case call depth and ISR nesting, enabling overflow check hooks during development
4. D.mutex protocol raising the holder to the priority of the highest waiter so it finishes quickly; FreeRTOS mutexes implement it, binary semaphores do not

Answer + AI explanation with Pro

1. A.ISR-safe APIs
2. B.Task and scheduler
3. C.Tick rate
4. D.Stack sizing

Answer + AI explanation with Pro

1. A.ISR-safe APIs — mutex protocol raising the holder to the priority of the highest waiter so it finishes quickly; FreeRTOS mutexes implement it, binary semaphores do not
2. B.ISR-safe APIs — each task owns a stack and a priority, and the scheduler runs the highest-priority ready task, switching pre-emptively on interrupts or the tick
3. C.ISR-safe APIs — functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined
4. D.ISR-safe APIs — Linux Foundation real-time OS with device-tree hardware description, Kconfig configuration, the west build tool and native Bluetooth, networking and MCUboot support

Answer + AI explanation with Pro

1. A.Linux Foundation real-time OS with device-tree hardware description, Kconfig configuration, the west build tool and native Bluetooth, networking and MCUboot support
2. B.a high-priority task blocked on a mutex held by a low-priority task that is itself pre-empted by medium-priority tasks, the failure behind the Mars Pathfinder resets
3. C.thread-safe FIFO copying items by value between tasks or from ISRs, with blocking send and receive plus timeouts, the recommended way to pass data out of interrupts
4. D.functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined

Answer + AI explanation with Pro

1. A.Stack sizing
2. B.Queue
3. C.Priority inheritance
4. D.Zephyr RTOS

Answer + AI explanation with Pro

1. A.Zephyr RTOS — semaphore signals events or counts resources and may be given from an ISR; mutex protects a shared resource, has an owner and supports priority inheritance
2. B.Zephyr RTOS — choose task stacks from high-water-mark measurement with margin for worst-case call depth and ISR nesting, enabling overflow check hooks during development
3. C.Zephyr RTOS — Linux Foundation real-time OS with device-tree hardware description, Kconfig configuration, the west build tool and native Bluetooth, networking and MCUboot support
4. D.Zephyr RTOS — a high-priority task blocked on a mutex held by a low-priority task that is itself pre-empted by medium-priority tasks, the failure behind the Mars Pathfinder resets

Answer + AI explanation with Pro

1. A.periodic timer interrupt, commonly 1 kHz via configTICK_RATE_HZ, driving time slicing, delays and timeouts, with tickless idle available to save power
2. B.mutex protocol raising the holder to the priority of the highest waiter so it finishes quickly; FreeRTOS mutexes implement it, binary semaphores do not
3. C.thread-safe FIFO copying items by value between tasks or from ISRs, with blocking send and receive plus timeouts, the recommended way to pass data out of interrupts
4. D.choose task stacks from high-water-mark measurement with margin for worst-case call depth and ISR nesting, enabling overflow check hooks during development

Answer + AI explanation with Pro

1. A.Priority inversion
2. B.Stack sizing
3. C.ISR-safe APIs
4. D.Task and scheduler

Answer + AI explanation with Pro

1. A.Stack sizing — thread-safe FIFO copying items by value between tasks or from ISRs, with blocking send and receive plus timeouts, the recommended way to pass data out of interrupts
2. B.Stack sizing — choose task stacks from high-water-mark measurement with margin for worst-case call depth and ISR nesting, enabling overflow check hooks during development
3. C.Stack sizing — functions ending in FromISR that never block and request a context switch through a higher-priority-task-woken flag; calling the normal versions from an interrupt is undefined
4. D.Stack sizing — mutex protocol raising the holder to the priority of the highest waiter so it finishes quickly; FreeRTOS mutexes implement it, binary semaphores do not

Answer + AI explanation with Pro