This paper addresses the problem of scheduling tasks with differentcriticality levels in the presence of I/O requests. In mixed-criticalityscheduling, higher criticality tasks are given precedence over those of lowercriticality when it is impossible to guarantee the schedulability of alltasks. While mixed-criticality scheduling has gained attention in recentyears, most approaches typically assume a periodic task model. Thisassumption does not always hold in practice, especially for real-time andembedded systems that perform I/O. In prior work, we developed ascheduling technique in the Quest real-time operating system, which integratesthe time-budgeted management of I/O operations with Sporadic Server schedulingof tasks. This paper extends our previous scheduling approach with support formixed-criticality tasks and I/O requests on the same processing core. Resultsshow that in a real implementation the mixed-criticality scheduling methodintroduced in this paper outperforms a scheduling approach consisting of onlySporadic Servers.

Multi- and many-core processors are becoming increasingly popular in embedded systems. Many of these processors now feature hardware virtualization capabilities, as found on the ARM Cortex A15 and x86 architectures with Intel VT-x or AMD-V support. Hardware virtualization provides a way to partition physical resources, including processor cores, memory, and I/O devices, among guest virtual machines (VMs). Each VM is then able to host tasks of a specific criticality level, as part of a mixed-criticality system with different timing and safety requirements. However, traditional virtual machine systems are inappropriate for mixed-criticality computing. They use hypervisors to schedule separate VMs on physical processor cores. The costs of trapping into hypervisors to multiplex and manage machine physical resources on behalf of separate guests are too expensive for many time-critical tasks. Additionally, traditional hypervisors have memory footprints that are often too large for many embedded computing systems. In this article, we discuss the design of the Quest-V separation kernel, which partitions services of different criticality levels across separate VMs, or sandboxes . Each sandbox encapsulates a subset of machine physical resources that it manages without requiring intervention from a hypervisor. In Quest-V, a hypervisor is only needed to bootstrap the system, recover from certain faults, and establish communication channels between sandboxes. This not only reduces the memory footprint of the most privileged protection domain but also removes it from the control path during normal system operation, thereby heightening security.

Quest-V is a separation kernel, which partitions a system into a collection of sandboxes. Each sandbox encapsulates one or more processing cores, a region of machine physical memory, and a subset of I/O devices. Quest-V behaves like a distributed system on a chip, using explicit communication channels to exchange data and migrate addresses spaces between sandboxes, which operate like traditional hosts. This design has benefits in safety-critical systems, which require continued availability in the presence of failures. Additionally, online faults can be recovered without rebooting an entire system. However, the programming model for such a system is more complicated. Each sandbox has its own local scheduler, and threads must communicate using message passing with those in remote sandboxes. Similarly, address spaces may need to be migrated between sandboxes, to ensure newly forked processes do not violate the feasibility of existing local task schedules. Migration may also be needed to move a thread closer to its required resources, such as I/O devices that are not directly available in the local sandbox. This paper describes how Quest-V performs real-time communication and migration without violating service guarantees for existing threads.

Multi- and many-core processors are becoming increasingly popular in embedded systems. Many of these processors now feature hardware virtualization capabilities, such as the ARM Cortex A15, and x86 processors with Intel VT-x or AMD-V support. Hardware virtualization offers opportunities to partition physical resources, including processor cores, memory and I/O devices amongst guest virtual machines. Mixed criticality systems and services can then co-exist on the same platform in separate virtual machines. However, traditional virtual machine systems are too expensive because of the costs of trapping into hypervisors to multiplex and manage machine physical resources on behalf of separate guests. For example, hypervisors are needed to schedule separate VMs on physical processor cores. In this paper, we discuss the design of the Quest-V separation kernel, which partitions services of different criticalities in separate virtual machines, or sandboxes. Each sandbox encapsulates a subset of machine physical resources that it manages without requiring intervention of a hypervisor. Moreover, a hypervisor is not needed for normal operation, except to bootstrap the system and establish communication channels between sandboxes.

Some people cannot use their hands to control a computer mouse due to conditions such as cerebral palsy or multiple sclerosis. For these individuals, there are various mouse-replacement solutions. One approach is to enable them to control the mouse pointer using head motions captured with a web camera. One such system, the Camera Mouse, uses an optical flow approach to track a manually-selected small patch of the subject’s face, such as the nostril or the edge of the eyebrow. The optical flow tracker may lose the facial feature when the tracked image patch drifts away from the initially-selected feature or when a user makes a rapid head movement. To address the problem of feature loss, we developed and incorporated the Kernel-Subset-Tracker into the Camera Mouse. The Kernel-Subset-Tracker is an exemplar-based method that uses a training set of representative images to produce online templates for positional tracking. We designed the augmented Camera Mouse so that it can compute these templates in real time, employing kernel techniques traditionally used for classification. We propose three versions of the Kernel-Subset-Tracker , each using a different kernel, and compared their performance to the optical-flow tracker under five different experimental conditions. Our experiments with test subjects show that augmenting the Camera Mouse with the Kernel-Subset-Tracker improves communication bandwidth statistically significantly. Tracking of facial features was accurate, without feature drift, even during rapid head movements and extreme head orientations. We conclude by describing how the Camera Mouse augmented with the Kernel-Subset-Tracker enabled a stroke-victim with severe motion impairments to communicate via an on-screen keyboard.

This paper describes a real-time USB 2 subsystem for the Quest operating system. Quest is designed for real-time embedded systems. Such systems need to interact with their environment using sensors and actuators. On many embedded platforms today there is support for basic serial, USB 2.0 and 100 Mbps Ethernet. Of these, USB 2.0 supports the highest throughput, while also supporting real-time communication. We show how the Quest USB 2.0 sub-system improves upon some of the deficiencies in USB software stacks in systems such as Linux through experimental evaluation. We demonstrate that the Quest USB sub-system is capable of predictable bandwidth allocation and increased overall performance. By dynamically reordering transaction requests, Quest's USB sub-system is able to avoid unnecessary admission control rejections. Additionally, we are able to provide real-time guarantees for asynchronous USB transactions such as bulk transfers, which are typically treated in a best-effort manner. Real-time guarantees for bulk transactions are necessary for any system interacting with devices that implement bulk endpoints such as in a real-time file system. The paper also introduces an algorithm for USB scheduling that accepts more requests and provides bulk transfer guarantees, for cases where Linux fails.

Users of mouse-replacement interfaces may have difficulty conforming to the motion requirements of their interface system. We have observed users with severe motor disabilities who controlled the mouse pointer with a head tracking interface. Our analysis shows that some users may be able to move in some directions easier than other directions. We propose several mouse pointer mappings that adapt to the user's movement abilities. These mappings will take into account the user's motions in two-or three-dimensions to move the mouse pointer in the intended direction.

Customizable Keyboard is an on-screen keyboard designed to be flexible and expandable. Instead of giving the user a keyboard layout Customizable Keyboard allows the user to create a layout that is accommodating to the user's needs. Customizable Keyboard also allows the user to select from a variety of ways to interact with the keyboard including but not limited to using the mouse pointer to select keys and different types of scan based systems. Customizable Keyboard provides more functionality than a typical onscreen keyboard including the ability to control infrared devices such as TVs and send Twitter® Tweets.