Behind the datasheet: HW-RTOS

 The Industrial Internet of Things (IIoT) relies heavily on data transfer, and as the volume of data being moved around increases, so do the demands on the limited resources available in endpoint devices such as sensors and actuators. One way to minimize the software burden is through the use of hardware accelerators.


Embedded systems often use some form of the operating system, particularly if they are based on modern 32-bit cores like the Arm Cortex-M family. Real-time operating systems (RTOS) are widely used due to the benefits they offer, but what can engineers do if they need to maintain hard real-time execution? One approach is to make full use of the hardware features offered by the processing platform.


An operating system is typically software that interacts with hardware at a low level. RTOS extends this by providing ways to guarantee that things happen just when you want them to. However, this can create conditions where the software and hardware compete for control. To mitigate these issues, RTOS uses techniques such as ticks, semaphores, and interrupt service routines. These features are normally software-based.


The HW-RTOS, or hardware RTOS, is a proprietary system that aims to implement these features in hardware and access them through APIs. This approach offers low interrupt latency with low jitter and very short interrupt disable periods. By taking a dedicated hardware approach, the HW-RTOS handles the tasks that could make an RTOS less responsive.


One of the key features of the Renesas HW-RTOS is tick offloading. By handling the process of measuring elapsed time in hardware, the RTOS doesn’t have to stop executing its current task just to mark time. This results in higher precision as there is no variation in time measurement.


Interrupt servicing is also a crucial aspect of real-time system design. A RTOS handles interrupts by switching to the relevant service routine when an interrupt is detected. However, if another interruption is asserted during that time, it could be missed. The normal approach is to switch between tasks when servicing interrupts, but this can result in long periods of time when no tasks are being executed.


In the HW-RTOS, the interrupt service routine is handled in hardware. This reduces the load on the CPU and shortens the time during which interrupts are disabled. It also reduces context switching. The HW-RTOS works through APIs, and to the host operating system, it looks like a peripheral on the system bus. Renesas has created a library for using the three registers that control the HW-RTOS: the API register, the argument register, and the result register.


The HW-RTOS is available in the RZ/N1D, RZ/N1S, and RZ/N1L processors from Renesas. For more information, including a full list of the APIs it supports, visit the Renesas website.


In conclusion, the HW-RTOS is a proprietary system that aims to solve the issues of real-time system design by offloading tasks to hardware. This approach offers low interrupt latency, low jitter, and very short interrupt disable periods. It is available in the RZ/N1D, RZ/N1S, and RZ/N1L processors from Renesas and can be accessed through APIs. By implementing RTOS features in hardware, the HW-RTOS helps to improve system responsiveness and reduce disruption from isolated events, making it an ideal solution for real-time applications in the IIoT.

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