HVAC Control in the New Millennium.pdf - HVAC.Amickracing

HVAC Control in the New MillenniumProcesses and ThreadsIn Win32 terminology, a process is defined as an instance of a runningapplication. Windows CE, like other 32-bit Windows platforms, isa multitasking OS that supports multiple threads of execution within arunning process. Thread management includes scheduling, synchronizationand resource allocation. These are handled by the kernel.Inside the processes that run on 32-bit Windows platforms are thethreads that rely on messages to start processing, control system resourcesand communicate with the OS and user. Windows messages canoriginate from a variety of sources, including the OS, keyboard, mouseor touch screen actions and other running processes or threads.Exception and Device HandlingSections of code that could fail due to hardware resource problems,device conflicts or coding errors need to be protected. Exception handlingprotects the application from termination or other system-levelproblems.The software interface must be able to manage simultaneous ornearly simultaneous events from different types of devices in the system.The Win32 API supports both synchronous and asynchronousmethods of device access. In a synchronous interface, the software requestsan action from a device and then waits for the result. Examplesinclude reading and writing files. In an asynchronous interface, thedevice requests services from the application. An example of an asynchronousdevice is a keyboard.In the Windows CE kernel, interrupt handling is split into interruptservice routing (ISR) and the interrupt service thread (IST).Keeping the routing as small and fast as possible is important forreal-time applications.At the hardware level, each interrupt request (IRQ) line is associatedwith one specific software ISR. When triggered, the ISR directs thekernel to the location of the IST.Interrupts have a priority associated with them. Windows CE usesa priority-based, time-slice algorithm for thread scheduling. The EmbeddedToolkit allows tuning of the interrupt timing and priorities for aspecific application.©2001 by The Fairmont Press, Inc. All rights reserved.