Southampton: Oct 99AMULET3i - 1 AMULET3i - asynchronous SoC Steve Furber - n Agenda: AMULET3i Design tools Future problems

Southampton: Oct 99AMULET3i - 2 AMULET3 n a third generation asynchronous ARM performance comparable with ARM9 radically new internal organisation –based on reorder buffer –Harvard core, unified I/D memory n under development within the OMI ATOM project first application as as part of a telecommunications controller

Southampton: Oct 99AMULET3i - 3 AMULET3i SoC organisation

Southampton: Oct 99AMULET3i - 4 AMULET3i - physical layout

Southampton: Oct 99AMULET3i - 5 AMULET3 core organisation n Harvard core forward from reorder buffer out-of-order completion in-order register update aborts handled at writeback

Southampton: Oct 99AMULET3i - 6 AMULET3H local bus RAM n segmented memory I & D ports arbitrate at each block quad-word I & D line buffers

Southampton: Oct 99AMULET3i - 7 AMULET3 tools n LARD behavioural modelling tool for async design 10x designer productivity vs Asim n Petrify much enhanced FORCAGE descendant can handle wider range of circuits n Balsa synthesis tool used for DMA controller

Southampton: Oct 99AMULET3i - 8 Tools - LARD n Language for Asynchronous Research and Development parallel processes with communication primitives extensive data types modelling of elapsed time used to model AMULET3 available from AMULET web site

Southampton: Oct 99AMULET3i - 9 Tools - LARD n Features time view block view HLL debug test generation co-simulation n Platforms UNIX/Linux

Southampton: Oct 99AMULET3i - 10 Tools - BALSA n Synthesis system for asynchronous circuits similar to Philips ‘Tangram’ used for AMULET3H DMA controller direct HLL to netlist compilation –syntax directed translation peephole optimisation

Southampton: Oct 99AMULET3i - 11 Tools - BALSA

Southampton: Oct 99AMULET3i - 12 Tools - Petrify n Petri Net modelling tool for low-level asynchronous circuits speed-independent synthesis technology mapping very powerful –can be tricky to use extensively used to design AMULET3 modules

Southampton: Oct 99AMULET3i - 13 AMULET3 validation n workstations now powerful enough to run ARM validation suite under TimeMill around 8 CPU-weeks total n testing full functionality now very hard very complex system-on-chip n design aimed at high performance timing margins much reduced validation complex and uncertain

Southampton: Oct 99AMULET3i - 14 AMULET3 - problems n high performance target timing margins must be small timing is hard to verify –very dependent on accurate extraction, models n modelling tools are imperfect e.g. crosstalk –bus wire delay 1.5ns +/- 1ns crosstalk –careful layout gives 0.9ns +/- 0.15ns how can we be sure such factors are OK?

Southampton: Oct 99AMULET3i - 15 The Future n timing accuracy is getting harder wire delays will become more significant crosstalk will get worse on-chip transistor variance will increase higher speeds will lead to higher noise n will delay-matching be viable? alternatives are dual-rail or other DI codes –incur significant area and power overheads

Southampton: Oct 99AMULET3i - 16 Gate vs (2mm) wire delays, ps

Southampton: Oct 99AMULET3i - 17 Alternatives to bundled data n Delay-insensitive codes timing encoded in data dual-rail encoding –100% area overhead c.f. bundled data –significant power cost –e.g. NCL from Theseus deal just announced with Motorola use conventional synthesis tools timing closure ceases to be an issue

Southampton: Oct 99AMULET3i - 18 Alternatives to bundled data n Delay-insensitive codes N-of-M codes –3-of-6 code 50% area overhead 3 transitions to send 4 bits –2-of-7 code 75% area overhead 2 transitions to send 4 bits –well-suited to inter-chip communication –may suit on-chip buses

Southampton: Oct 99AMULET3i - 19 Conclusions n complex async design is feasible standard tools are just about survivable additional tools improve productivity n ideal design flow: LARD-like specification formal verification of high-level properties automated synthesis onto module library n timing closure is the major problem may ultimately rule out bundled data