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Introduction As we discussed in Chapter 13, co-operative schedulers provide a predictable platform for a wide range of embedded applications. On some occasions, it can be necessary to incorporate some of the features of preemptive schedulers into a co-operative scheduler framework, in a carefully controlled manner. A hybrid scheduler seeks to achieve this.
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Multi-stage task Context ● You are developing an embedded application using one or more members of the 8051 family of microcontrollers. ● The application has a time-triggered architecture, constructed using a scheduler. Problem How do you make sure that a long task does not interfere with the normal operation of the scheduler? Background See CO […]
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Two patterns in this chapter encapsulate key design characteristics that underlie many successful co-operatively scheduled applications: ● MUL TI – ST AGE T ASK [page 317] considers techniques that may be used to convert long tasks (scheduled at infrequent intervals) into much shorter tasks (scheduled at frequent intervals) ● MUL TI – ST A TE […]
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Introduction The creation of accurate delays are key requirements in many embedded applications. In this chapter we will consider two different techniques that may be used to pro- vide such facilities: ● HARDW ARE DELA Y [page 194] which is capable of producing precise delays through the use of one of the on-chip timers. Particularly […]
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Hardware watchdog Context ● You are developing an embedded application using one or more members of the 8051 family of microcontrollers. ● You are designing an appropriate software foundation for your application. Problem How can you ensure that – if your application ‘hangs’ due to an unexpected software or hardware error – the system will […]
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Software delay Context ● You are developing an embedded application using one or more members of the 8051 family of microcontrollers. ● You are designing an appropriate software foundation for your application. Problem How do you create a simple delay without using any hardware (timer) resources? Background See HARDW ARE DELA Y [page 194] for […]
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Port I/O Context ● You are developing an embedded application using one or more members of the 8051 family of microcontrollers. ● You are designing an appropriate software foundation for your application. Problem How do you write software to read from and /or write to the ports on an (8051) microcontroller? Background The Standard 8051s […]
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Port header Context ● You are developing an embedded application using one or more members of the 8051 family of microcontrollers. Problem How do you manage port access allocations in a larger project? Background In a typical embedded project, you may have a user interface created using an LCD, a keypad and one or more […]
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Introduction Suppose there is a hungry dog guarding a house (Figure 12.1), and someone wishes to break in. If the burglar’s accomplice repeatedly throws the guard dog small pieces of meat at 2-minute intervals, then the dog will be so busy concentrating on the food that he will ignore his guard duties and will not […]
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In this chapter, we see that schedulers can play a similar role in embedded systems to that played by ‘Windows’ (or other operating systems) in many modern desktop applications. Introduction Having laid the foundations in Parts A and B, we are now in a position to look in detail at the ways in which time-triggered […]
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