AMULET microprocessor

AMULET is a series of microprocessors that implement the ARM processor architecture. Developed by the Advanced Processor Technologies group under the University of Manchester's computer science school (formerly the AMULET and PAL groups based at the same institution), AMULET is unique from other ARM implementations in that it is an asynchronous microprocessor, not making use of a square wave clock signal for data synchronization and movement.

[edit] List of AMULET microprocessors

AMULET1 - Designed in 1990 and first fabricated in 1993. Its estimated performance is approximately 70% of that of a comparably-sized synchronous ARM6 running at 20 MHz.
AMULET2 - A re-implementation of AMULET1 first fabricated in 1996. Features on-chip memory that can be used either as processor cache or mapped RAM. The APT group estimates AMULET2 to have a similar power dissipation/performance ratio as ARM8. One very notable feature that is due to the asynchronous design is that the power dissipation drops to 3 μW when not in use (assuming the on-board timer, which handles DRAM refresh, is also inactive).
AMULET3 - This was a redesigned architecture aiming at higher performance than the previous AMULET processors whilst retaining low power dissipation. Fabricated in 2000 it supported the ARM level 4 instruction set compatibility, as well as support Thumb mode (i.e. ARM9TM). Performance and power dissipation were approximately the same as an ARM9 fabricated on the same technology. AMULET3 was employed in a commercial prototype DECT device because of its inherent low EMI characteristics. This did not go into manufacture for non-technical reasons.