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by brandmeyer
2622 days ago
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Most RTOSen allow you to access a minimal set of kernel services from interrupt context, so that you can implement the standard top-half/bottom-half driver processing model. NuttX's managed interrupts are in this category, and almost any driver's interrupt handler needs to be as well. Almost any RTOS on the Cortex-M profile will fully utilize the NVIC, giving you a hardware-managed preemptive FIFO scheduler even in interrupt context. NuttX's lack of this feature is a severe weakness, and a major reason to avoid using it. Additionally, some RTOSen will provide the ability to install interrupt handlers that cannot safely access any kernel services. These are usually not capable of doing much more than provide user-defined error handling prior to taking a reboot. NuttX's raw interrupts are in this category. |
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I think this is a miconception about how RTOS's can work. Certainly in a bare-metal environment (or with a minimum RTOS), prioritized interrrupt-level processing is critical. But with RTOS's like NuttX, interrupts should be very brief: You should enter the handler, perform mimimal housekeeping, and signal a prioritized thread to perform the interrupt-related operations.
This is not a oversight in the design, it is intentional replacement of prioritized interrupt handling processing with priorotized multi-tasking processing.
The NuttX interrupt handling is designed so that the context switch after signaling the prioritized thread is ZERO. The return from interrupt vectors directly in the prioritized task (assuming it is the highest priority). This is all intentional design and is very efficent in these regards.
There is no one-size, fits all RTOS. You find that some are too minimal and primitive to meet your needs (I am thinking FreeRTOS, ChibiOS, Zephyr, ...) and some may be heavier weight than is necessary for your purposes (perhaps NuttX, nucleus, RTEMS, ...) or even heavier (VxWorks, QNX, Integrity, and on up to Linux). If you want the features of one class of RTOS, then you will find the others flawed in various ways, whichever RTOS is that one that meets your needs. It is a kind of Goldilocks effect.