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Unformatted text preview: the need for off-chip memory completely, several have a few kilobytes of on-chip RAM which can be loaded with critical routines to save power (and improve performance). Several of the chips incorporate clock control circuitry which reduces the clock frequency (or stops the clock altogether) when the chip is not fully loaded, and switches the clock to individual modules off when they are inactive. The chips are mainly based upon static or pseudo-static CMOS technology where, with a little care, digital circuits only consume power when they switch. Some of the chips also incorporate analogue functions which require continuous bias currents, so these circuits can usually be powered down when they are inactive. Exercise 13.2.1 In embedded systems there is usually no 'reset' button to restart a system that has crashed. What techniques are used to recover from software crashes? Exercise 13.1.2 Exercise 13.1.3 Example 13.2 Examples and exercises 373 Exercise 13.2.2 Several of the chips described in this chapter incorporate counter/timer modules. What are these used for? The ARM7500 has an on-chip cache, AMULET2e (see Section 14.4 on page 384) has on-chip memory which can be configured either as a cache or as directly addressed memory, and Ruby II and VIP simply have directly addressed on-chip memory. Explain the difference between on-chip RAM and an on-chip cache and explain why the designers of these chips made the choices that they did. Exercise 13.2.3 The AMULET Asynchronous ARM Processors Summary of chapter contents
The AMULET processor cores are fully asynchronous implementations of the ARM architecture, which means that they are self-timed and operate without any externally supplied clock. Self-timed digital systems have potential advantages in the areas of power-efficiency and electromagnetic compatibility (EMC), but they require a radical redesign of the system architecture if the asynchronous timing framework is to be fully exploited, and designers need to learn a new mind set if they a...
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- Spring '09