Amulet3 includes a zero power halt instruction as did

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Unformatted text preview: oved into its slot. Forwarding from the reorder buffer requires a search of the buffer contents. Conditional ARM instructions may or may not return valid results to the buffer; multiple instructions may use the same destination register. Identifying the most up-to-date value for a particular register potentially requires waiting for a result to become available in a slot, seeing that it is invalid, and then (worst case) searching all the other slots in series. This case is rare, though, and is easily accommodated by the asynchronous timing framework. The write-back stream delivered by the reorder buffer is in program order, so this stage of the pipeline simply delivers values to the register file, checking each one for validity and looking for any memory faults. If a fault is detected an exception is raised and subsequent results are discarded unti\ the exception handling, mechanism has activated. Data memory interface Reorder buffer Register write 390 The AMULET Asynchronous ARM Processors Figure 14.11 The AMULETS reorder buffer organization. AMULETS performance The performance characteristics of AMULET3 are summarized in Table 14.4. It can be seen that the objective of achieving comparability with the ARM9TDMI on the same process has been met. AMULET3 has been used as the processing core in the DRACO telecommunications controller; this is the subject of the next section. Table 14.4 AMULET3 characteristics. Process Metal layers Vdd 0.35 urn Transistors 3 Core area 3.3V Clock 113,000 MIPS 3 mm2 Power none MIPS/W 120 154mW 780 14.6 The DRACO telecommunications controller The DRACO (DECT Radio Communications Controller) chip is the first commercial design based on AMULET technology; it uses the AMULET3H self-timed processing subsystem described later in this section as its compute and control engine. DRACO was developed in collaboration between Hagenuk GmbH (who designed the clocked telecommunications peripherals) and the University of Manchester (who were responsible for the AMULETS H subsystem) with funding from the European Union. The DRACO telecommunications controller 391 Rati...
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