Multicore PC-class embedded systems present an opportunity to consolidate separate microcontrollers as software-defined functions. For instance, an automotive system with more than 100 electronic control units (ECUs) could be replaced with one or, at most, several multicore PCs running software tasks for chassis, body, powertrain, infotainment, and advanced driver assistance system (ADAS) services. However, a key challenge is how to handle real-time device input and output (I/O) and host-level networking as part of sensor data processing and control. A traditional microcontroller would commonly feature one or more Controller Area Network (CAN) buses for real-time I/O. CAN buses are usually absent in PCs, which instead feature higher bandwidth Universal Serial Bus (USB) interfaces. This article shows how to achieve real-time device I/O and host-to-host communication over USB, using suitably written device drivers and a time-aware POSIX-like “tuned pipe” abstraction. This allows developers to establish task pipelines spanning one or more hosts, with end-to-end latency and throughput guarantees for sensor data processing, control, and actuation.

Complex embedded systems are now supporting the co-existence of multiple OSes to manage services once assigned to separate embedded microcontrollers. Automotive systems, for example, now use multiple OSes to consolidate electronic control unit (ECU) functions on a centralized embedded computing platform. Such platforms have the complexity of an industrial embedded PC, with multiple cores and hardware virtualization capabilities. This enables a partitioning hypervisor to spatially and temporally share the physical machine with separate guest OSes, which manage services of different criticality levels. However, PC-class hardware incurs a large latency to bootstrap an OS and associated application-level services. A firmware BIOS performs a power-on-self-test, and then loads OS images into memory from a bootable storage device. This latency is unacceptable in time-critical embedded systems, where important services must be operational within milliseconds of starting the system. In this paper, we present Jumpstart, a PC-class power management approach that minimizes the wakeup delay of a partitioning hypervisor for use in embedded systems. We show how Jumpstart resumes critical OS services and tasks from a low power suspended state in approximately 600 milliseconds, and reduces full system startup delay by a factor of 23. Additionally, Jumpstart consumes minimal power compared to approaches requiring a system boot from a previously powered-off state. By comparison, an alternative firmware-optimized bootloader, called Slim, reduces boot latency by a factor of 1.8.

Over-estimation of worst-case execution times (WCETs) of real-time tasks leads to poor resource utilization. In a mixed-criticality system (MCS), the over-provisioning of CPU time to accommodate the WCETs of highly critical tasks may lead to degraded service for less critical tasks. In this paper we present PAStime, a novel approach to monitor and adapt the runtime progress of highly time-critical applications, to allow for improved service to lower criticality tasks. In PAStime, CPU time is allocated to time-critical tasks according to the delays they experience as they progress through their control flow graphs. This ensures that as much time as possible is made available to improve the Quality-of-Service of less critical tasks, while high-criticality tasks are compensated after their delays. This paper describes the integration of PAStime with Adaptive Mixed-criticality (AMC) scheduling. The LO-mode budget of a high-criticality task is adjusted according to the delay observed at execution checkpoints. This is the first implementation of AMC in the scheduling framework of LITMUS^RT, which is extended with our PAStime runtime policy and tested with real-time Linux applications such as object classification and detection. We observe in our experimental evaluation that AMC-PAStime significantly improves the utilization of the low-criticality tasks while guaranteeing service to high-criticality tasks.

This paper presents Boomerang, an I/O system that integrates a legacy non-real-time OS with one that is customized for timing-sensitive tasks. A relatively small RTOS benefits from the pre-existing libraries, drivers and services of the legacy system. Additionally, timing-critical tasks are isolated from less critical tasks by securely partitioning machine resources among the separate OSes. Boomerang guarantees end-to-end processing delays on input data that requires outputs to be generated within specific time bounds.We show how to construct composable task pipelines in Boomerang that combine functionality spanning a custom RTOS and a legacy Linux system. By dedicating time-critical I/O to the RTOS, we ensure that complementary services provided by Linux are sufficiently predictable to meet end-to-end service guarantees. While Boomerang benefits from spatial isolation, it also outperforms a standalone Linux system using deadline-based CPU reservations for pipeline tasks. We also show how Boomerang outperforms a virtualized system called ACRN, designed for automotive systems.

A fundamental problem in real-time computing is handling device input and output in a timely manner. For example, a control system might require input data from a sensor to be sampled and processed at a regular rate so that output signals to actuators occur within specific delay bounds. Input/output (I/O) devices connect to the host computer using different types of bus interfaces. One of the most popular interfaces in use today is the universal serial bus (USB). USB is now ubiquitous, in part due to its support for many classes of devices with simplified hardware needed to connect to the host. However, typical USB host controller drivers suffer from potential timing delays that affect the delivery of data between tasks and devices. Consequently, this paper introduces tuned pipes, a host controller driver and system framework that guarantees end-to-end latency and throughput requirements for I/O transfers. We expand on our earlier work involving USB 2.0 to support higher bandwidth USB 3.x communication. As a case study, we show how a USB-Controller Area Network (CAN) guarantees temporal isolation and end-to-end guarantees on communication between a set of peripheral devices and host tasks. A comparable USB-CAN bus setup using Linux is not able to achieve the same level of temporal guarantees, even when using SCHED_DEADLINE.