Datasheet

Chapter 1: Windows Embedded CE
6
Real - Time Operating System
Windows Embedded CE is a hard real - time operating system, providing reliable core services to support
embedded system designs that demand low - latency, deterministic, real - time system performance.
CE has the following features required by a real - time system:
Preemptive Multithreading — Determines when a context switch should occur.
Prioritized Thread Scheduling — Uses a priority - based time - slice algorithm to schedule
threads.
Priority Inversion Prevention — When a lower - priority thread is sharing the same resource
with a higher - priority thread, priority inversion can occur when the lower - priority thread and
the higher - priority thread are competing for the same resource.
Predictable Thread Synchronization — When multiple threads compete for resources, it ’ s
necessary to manage and synchronize thread priority. Otherwise, priority inversion can occur.
❑
❑
❑
❑
With a smaller OS runtime footprint, it takes less system memory, less storage, and
fewer processor resources to run. Devices with smaller OS run time take less time to
boot up, which helps provide an efficient device. By minimizing the OS footprint,
the device can be built with less expensive hardware.
There are hard real-time and soft real-time systems. A soft real-time system can miss
its bounded time response, missing the timing deadline once in a while, and still
maintain a reasonable level of acceptable performance. For example, a Voice over IP
(VoIP) device may delay the delivery of voice packets once in a while and end up
dropping some of the packets because of network traffic loading, but still provide
acceptable performance. A hard real-time system cannot miss any of its bounded
time responses. When a hard real-time system misses a bounded time response, it
causes major system failure. Imagine what happens when an automobile’s electronic
brake system fails to engage in a timely manner while the automobile is traveling at
high speed and needs to make an urgent stop to avoid a collision. In a real-time sys-
tem, the bounded time response means that the system must respond to service an
event, such as the interrupt, within a maximum allowable time defined by the sys-
tem. Otherwise, a major failure will occur.
Supported Hardware
Windows Embedded CE is designed to run on hardware built with x86, ARM, MIPS, and SH4 processors.
Business statistics indicate that only about 2 percent of the total number of microprocessors are used to
build desktop PCs. The other 98 percent are used to build non - PC devices for the embedded market.
The ability to support four processor families enables Windows Embedded CE to reach a much broader
market than the PC market and creates broader employment opportunities for the “ embedded ”
developer and development of new types of devices.
c01.indd 6c01.indd 6 9/26/08 5:11:10 PM9/26/08 5:11:10 PM