On Fri, May 17, 2024 at 1:42 AM 吳岱儒 <tjwu1...@gmail.com> wrote:
> Hi community, > > Is Nuttx a hard real time RTOS or software RTOS? > If Nuttx support hard real time, is there any documentation about this > feature and design ? > > BRs, > TaiJuWu > Hello, It depends on the CPU architecture: For example, on ARM Cortex M architecture, the hardware provides an interrupt vector table which supports multiple interrupt vectors, and multiple interrupt priority levels, and there is an interrupt base priority register which allows to keep certain interrupts enabled while most interrupts are disabled. This hardware support makes it possible to implement what we call a "Zero Latency Interrupt" (sometimes called a Raw Interrupt or Unmanaged Interrupt by other RTOSes). To get a hard real time performance, you would identify the time-critical part of your software that needs zero latency handling (usually a tiny part of the whole software) and then design your software to run that part in a Zero Latency Interrupt. Everything else goes in regular code. There is a page in the NuttX documentation that explains Zero Latency Interrupts. See [1]. It may be possible to implement Zero Latency Interrupts for other CPU architectures besides ARM Cortex M, if the hardware provides mechanisms that make it possible, such as a way to define a high priority interrupt that is never disabled. For the best possible performance, you need to choose your microcontroller hardware carefully. Look for features like the ability to put your zero latency interrupt handler and its variables in RAM for faster execution (because code in FLASH may take longer to fetch). Some microcontrollers even have a special section of RAM that is faster than the rest for this exact purpose. For example the STmicro STM32G series has this feature and calls it CCM SRAM. Other microcontroller vendors might have a similar thing but call it a different name. Fortunately NuttX supports many CPU architectures and many microcontroller models from many hardware vendors, so you have lots of choices. Also if the microcontroller you want to use isn't currently supported by NuttX, it is usually not too difficult to add support, especially if there is already support for something similar. References: [1] https://nuttx.apache.org/docs/12.5.0/guides/zerolatencyinterrupts.html Hope this helps, Nathan
