barcode reader application in asp.net PIC18 RTOS Design in Software

Draw QR-Code in Software PIC18 RTOS Design

PIC18 RTOS Design
Scan Denso QR Bar Code In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Encoding Quick Response Code In None
Using Barcode generation for Software Control to generate, create QR Code image in Software applications.
It is possible to implement an RTOS in the PIC18 architecture owing to the processor s ability to access the program counter stack. This feature allows the return address context information that is required to restore execution of the thread to be read or written by the RTOS task-switching code. Unlike other processors, the PIC18 does not place all context data onto the stack, which means that other means will have to be used to save the context information and then restore it into the appropriate registers. With a strategy that allows the saving of the return address information along with the context registers, you should be able to create an RTOS for the PIC18 architecture quite easily. There are a number of ways to save the context registers to ensure that the thread switching is fast and that the appropriate registers are saved and then retrieved. Probably the simplest way of doing this is to access all thread local variables via an index register with an offset; by doing this, the context registers (including the saved program
QR-Code Decoder In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
Create QR In Visual C#
Using Barcode generator for VS .NET Control to generate, create QR Code image in .NET applications.
PIC18 RTOS DESIGN
Drawing QR In Visual Studio .NET
Using Barcode maker for ASP.NET Control to generate, create Quick Response Code image in ASP.NET applications.
Quick Response Code Creator In .NET Framework
Using Barcode maker for Visual Studio .NET Control to generate, create Quick Response Code image in Visual Studio .NET applications.
counter stack information) are pushed onto the stack using the POSTDEC INDF register, and when it is time to change the thread, the index register pointing to the stack information is changed to the next thread. A slower and more cumbersome way would be to copy all the thread context registers (including the program counter) into a memory space that is unique to the thread. Saving and restoring the context registers is the most important aspect of the design of the RTOS; you must have a methodology that is both ef cient and reliable the task switch must be fast and accurate, or your applications will not execute properly, and this is a very dif cult bug to nd and x. I must point out that the PIC18 architecture does not implement a memory management unit (MMU) that will ag conditions where memory is accessed inappropriately or attempts to execute beyond the con nes of the thread. In most modern 32- and 64-bit processors, the MMU will provide protection between processes to ensure that threads do not overwrite critical portions of memory. Another important feature of an MMU is to move physical memory in and out of speci c address ranges of the executing thread (this is known as virtual memory), and this allows the le system to load information for a thread in convenient locations and not have to relocate memory to make space for new information. The MMU function as relating to program memory is really not required in the PIC18 because the program memory, for all intents and purposes, is hard-coded and cannot be changed during application execution le and special function registers should have some kind of protection in the PIC18 to ensure that they are accessed appropriately. When you are designing your own RTOS, you have to be careful of the fast stack built into call and return instructions, as well as executing in interrupt handlers. The registers saved on the fast stack are critical context registers, but you will nd that coming up with a way to read these values from the fast stack will be more dif cult and take more instructions than simply saving the register contents directly, as you would in an interrupt handler. It is easy to get lazy and rely on the fast stack for subroutines, but this is a habit that you should break in the case where a thread is suspended during a subroutine and the contents of the fast stack are overwritten by even interrupt requests. Finally, you will have to have a plan for the access bank le registers. These 128 le registers are very useful to use as general-purpose registers, and it would be easy to use them in your everyday programming, but you will have to take care as to how you use them in an RTOS situation. If you were to use them in the threads of your application, you would have to save these registers as part of the thread context information. This is a relatively lot of data to save and restore as part of the task-switching operation, and it should really be avoided at all costs. Using a strategy such as only employing a stack pointer for local thread variables avoids the need for using the access bank le registers and will help you to keep the movement of your context-saving information to an absolute minimum. In the following sections I will outline the design for a PIC18 RTOS and provide you with a simple application to demonstrate operation of the threads. It is important to remember that there is not only one way to implement an RTOS for the PIC18 (or other processors, for that matter), and I recommend that you spend some time researching the requirements of your application and work through a plan to switch between tasks and manage your le registers most ef ciently.
QR Code Printer In VB.NET
Using Barcode printer for .NET Control to generate, create Denso QR Bar Code image in Visual Studio .NET applications.
Draw Bar Code In None
Using Barcode drawer for Software Control to generate, create barcode image in Software applications.
Encode EAN-13 Supplement 5 In None
Using Barcode generation for Software Control to generate, create European Article Number 13 image in Software applications.
Draw ANSI/AIM Code 128 In None
Using Barcode printer for Software Control to generate, create ANSI/AIM Code 128 image in Software applications.
Create Bar Code In None
Using Barcode encoder for Software Control to generate, create barcode image in Software applications.
Drawing USS-128 In None
Using Barcode maker for Software Control to generate, create GS1 128 image in Software applications.
2 Of 5 Interleaved Generation In None
Using Barcode maker for Software Control to generate, create I-2/5 image in Software applications.
Generating UPC Code In None
Using Barcode creator for Online Control to generate, create UPC-A Supplement 5 image in Online applications.
DataMatrix Maker In None
Using Barcode maker for Microsoft Excel Control to generate, create ECC200 image in Excel applications.
Creating UPC A In Java
Using Barcode creation for Java Control to generate, create Universal Product Code version A image in Java applications.
Printing Bar Code In VB.NET
Using Barcode maker for .NET Control to generate, create bar code image in VS .NET applications.
Scanning Code 3 Of 9 In VS .NET
Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in Visual Studio .NET applications.
GTIN - 13 Drawer In Java
Using Barcode creator for Java Control to generate, create EAN13 image in Java applications.
Bar Code Printer In Visual Studio .NET
Using Barcode encoder for ASP.NET Control to generate, create bar code image in ASP.NET applications.
Copyright © OnBarcode.com . All rights reserved.